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A new look to the yemeni geology based on new solutions to the most chaotic yemeni geological problems
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A new look to the yemeni geology based on new solutions to the most chaotic yemeni geological problems

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ABSTRACT ...

ABSTRACT
This is the first work, which introduce a new look to the Yemeni Geology. My interest in the Yemeni geology
started in 1987, when I wrote my first geological and technical report on Al-Kharg well, drilled in Al-Jawf Marib
Shabwa basin (Moscow, 1987; (Unpublished)). And my work on the former South Yemen regional geology
(Moscow, 1990; (Unpublished)) as a result of my fieldwork visits to the above-mentioned area.
During my work in the Republic of Yemen, (the research study area), for 8 years (1992-1999), I collected variably
detailed information of hundreds publications references on the pervious and the present geological activities in
Yemen for the period from 1852 until Today. That work led to the first classification and division for what I called the
Geological Research History Work (G.R.H.W) of the Republic of Yemen.
At the same time, I was highly interested in the whole pervious and present stratigraphic research related to the
Yemeni Lithostratigraphic Units and Nomenclature, because stratigraphic research pursued by different organizations,
companies and groups on different and indipendent lines was on the point of leading to choas. Studing a huge material
and data related to the pervious and the present geological activities in Yemen; such as final reports on geological
survey, different kinds of geophisical works, wells data (for more than 210 wells drilled in different area of the
republic of Yemen, where most of those wells located in the north-northeastern, east and south-southeastern part of
the Republic of Yemen(~75% of Yemeni sedimentary cover located in this area)), dry and wet sample analysis, well
site geologist geological descriptions, background gas indicatores, drillig results, log interpretations, core analysis, well
completion reports, lithostratigraphic units history (first time publication of the unit, its current meaning and definition),
lithostratigraphic and biostratigraphic description and indication of age; This research study work led at the beginning
to my work done on diferent geological wells data tables, geological well sections, correlation between wells (local
and regional), different kind of geological maps for spesific areas (this happened during my work in the Adeni Branch
of the Ministry of Oil and Mineral Resources) and led also to the first table on the whole Yemen Lithostratigraphic
Units and Nomenclture; my mapping and modelling to the whole eastern part of Yemen with the adjacent areas (this
happened during my research study work in Jilin University). This work is an extent to the great work done by many
4
interested geologists, scientific expeditions, organizations, local and forieghn companies, variably detailed information
of hundreds publications and references on the Yemeni geology.
The Yemeni Lithostratigraphic Units and Nomenclature table is projected to be a kind of huge encyclopedia. The
new thing is that names of all Yemeni lithostratigraphic units are presented in the above mentioned table in
accordance to their proven and high checked geological age. It is the first electronic and attributed table. Just point
your Computer mouse on the red triangle located on the right-upper corner of an interested lithostratigraphic units and
you are going to receive a brief geological information about it, especially in which Yemeni basins penetrated (Basin
name, It’s lithology, description and age).
The most important thing that this table led to my new explanation to the anomaly in the Yemeni
Lithostratigraphic Units and Nomenclature, having the same geological time line (the same age), by relating such
anomaly to the geological history of the area, especially the anomaly in tectonic activities and the process of
sedimentation; this table also gave me the right to suggest a new subdivision to the Yemeni Paleozoic sediments, into
two new depositional sequences, i.e. from young to old:
b. UPPER PALEOZOIC (Devonian – Permian) / TRIASSI

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  • 1. EARTH SCIENCE COLLEGE OF JILIN UNIVERSITY INSTITUTE OF GEOENERGY A NEW LOOK TO THE YEMENI GEOLOGY BASED ON NEW SOLUTIONS TO THE MOST CHAOTIC YEMENI GEOLOGICAL PROBLEMS IMPORTANT NOTICE: This Thesis include two patent: 1. The (3D.Y.G.M. – Tin For All): The Three Dimension Yemeni Geological Model – Tin For All 2. The (T.G.T.C.): Al-Tohaita (Ser Ya Kaos) Geological Time Clock Advisers : Prof. Wang Dong Po & Prof. Xue Lin Fu Student’s Name : Mohammed Darsi Abdulrahman Nedham Major : Geology Specialization : Geology (Subsurface Geology) 1
  • 2. CHANGCHUN – 2002 EARTH SCIENCE COLLEGE OF JILIN UNIVERSITY INSTITUTE OF GEOENERGY A NEW LOOK TO THE YEMENI GEOLOGY BASED ON NEW SOLUTIONS TO THE MOST CHAOTIC YEMENI GEOLOGICAL PROBLEMS IMPORTANT NOTICE: This Thesis include two patent: 1. The (3D.Y.G.M. – Tin For All): The Three Dimension Yemeni Geological Model – Tin For All 2. The (T.G.T.C.): Al-Tohaita (Ser Ya Kaos) Geological Time Clock Advisers : Prof. Wang Dong Po & Prof. Xue Lin Fu Student’s Name : Mohammed Darsi Abdulrahman Nedham Major : Geology Specialization : Geology (Subsurface Geology) 2
  • 3. CHANGCHUN – 2002 ABSTRACT This is the first work, which introduce a new look to the Yemeni Geology. My interest in the Yemeni geology started in 1987, when I wrote my first geological and technical report on Al-Kharg well, drilled in Al-Jawf Marib Shabwa basin (Moscow, 1987; (Unpublished)). And my work on the former South Yemen regional geology (Moscow, 1990; (Unpublished)) as a result of my fieldwork visits to the above-mentioned area. During my work in the Republic of Yemen, (the research study area), for 8 years (1992-1999), I collected variably detailed information of hundreds publications references on the pervious and the present geological activities in Yemen for the period from 1852 until Today. That work led to the first classification and division for what I called the Geological Research History Work (G.R.H.W) of the Republic of Yemen. At the same time, I was highly interested in the whole pervious and present stratigraphic research related to the Yemeni Lithostratigraphic Units and Nomenclature, because stratigraphic research pursued by different organizations, companies and groups on different and indipendent lines was on the point of leading to choas. Studing a huge material and data related to the pervious and the present geological activities in Yemen; such as final reports on geological survey, different kinds of geophisical works, wells data (for more than 210 wells drilled in different area of the republic of Yemen, where most of those wells located in the north-northeastern, east and south-southeastern part of the Republic of Yemen(~75% of Yemeni sedimentary cover located in this area)), dry and wet sample analysis, well site geologist geological descriptions, background gas indicatores, drillig results, log interpretations, core analysis, well completion reports, lithostratigraphic units history (first time publication of the unit, its current meaning and definition), lithostratigraphic and biostratigraphic description and indication of age; This research study work led at the beginning to my work done on diferent geological wells data tables, geological well sections, correlation between wells (local and regional), different kind of geological maps for spesific areas (this happened during my work in the Adeni Branch of the Ministry of Oil and Mineral Resources) and led also to the first table on the whole Yemen Lithostratigraphic Units and Nomenclture; my mapping and modelling to the whole eastern part of Yemen with the adjacent areas (this happened during my research study work in Jilin University). This work is an extent to the great work done by many 3
  • 4. interested geologists, scientific expeditions, organizations, local and forieghn companies, variably detailed information of hundreds publications and references on the Yemeni geology. The Yemeni Lithostratigraphic Units and Nomenclature table is projected to be a kind of huge encyclopedia. The new thing is that names of all Yemeni lithostratigraphic units are presented in the above mentioned table in accordance to their proven and high checked geological age. It is the first electronic and attributed table. Just point your Computer mouse on the red triangle located on the right-upper corner of an interested lithostratigraphic units and you are going to receive a brief geological information about it, especially in which Yemeni basins penetrated (Basin name, It’s lithology, description and age). The most important thing that this table led to my new explanation to the anomaly in the Yemeni Lithostratigraphic Units and Nomenclature, having the same geological time line (the same age), by relating such anomaly to the geological history of the area, especially the anomaly in tectonic activities and the process of sedimentation; this table also gave me the right to suggest a new subdivision to the Yemeni Paleozoic sediments, into two new depositional sequences, i.e. from young to old: b. UPPER PALEOZOIC (Devonian – Permian) / TRIASSIC (Lower Triassic) (?) a. LOWER PALEOZOIC (Cambrian (?) - Lower Silurian (Llandoverian)) And led to my new subdivision to the whole Phanerozoic sedimentary sequence of the Republic of Yemen into five depositional sequences, i.e. from young to old: e. OLIGOCENE / MIOCENE-RECENT d. CRETACEOUS (Lower Hauterivian to Maastrichtian) / PALEOCENE – MIDDLE EOCENE c. JURASSIC – CRETACEOUS (Lower Berriasian to Lower Valanginian) b. UPPER PALEOZOIC (Devonian – Permian) / TRIASSIC (Lower Triassic) (?) a. LOWER PALEOZOIC (Cambrian (?) - Lower Silurian (Llandoverian)) And led also to my new idel lithostratigraphic column suggested for the Whole Yemeni Phanerozoic sequence, and to my new suggestion, implies that the North Hadhramawt Arch became pronounced during the Lower Paleozoic as a result of uplift in Cambrian (?) - Lower Silurian (Llandoverian) times. 4
  • 5. At the end, I would like to fix in minds, that my personal field notices and records show, that the Yemeni Lithostratigraphic Units characterised by some important factors, such as Lithology changes, Rate of Penetration (increase and decrease), background gas (increase and decrease) and the chromatographic analysis. I am sure, that this work with the two projected patent methods (Chapter 9. 10 ) raised many important and interesting issues that required a great deal of continuous attention. In my opinion, to achieve a high result of my work, we must make things happen, didnot shirk from the tough decisions, and had a clear vision for entering into the 21st century. 5
  • 6. ACKNOWLEDGMENTS I would like to thank the Ministry of High Education (China),the Yemeni Ministry of Oil and Mineral Resources (Yemen), and the Earth Science College of Jilin University for everything they have done for me. I would like to express my deep gratitude and sincere thanks to my supervisors, Professor Wang Dong Po & Professor Xue Lin Fu, for their supervision, including their helpful guidance with all aspects of the work. Their consistent encouragement through my research work, constructive criticism and patient corrections of my manuscript during my thesis writing (the entire preliminary and final manuscript in exhaustive). I especially enjoyed many discussions, which we had during the past three years, which usually sparked many new ideas. Really, their supervision and enthusiasm throughout this project was greatly appreciated. I am also very grateful to Professor Wang Xi Kui for his Satellite images interpretation lectures and discussion, Professor Sun Feng Yue and Professor Yun Xuan Zhou. I wish to thank Dr. Rasheed S. Ba-Rabbah (the Minister of the Ministry of Oil and Mineral Resource), Dr. Ahmed Ali Abdella (Vice-President of P.E.P.B.- Sana’a), Dr. Nani A.O (the P.E.P.B President ’s Consultant & Advisor), Mr. Haitam F. M. Saeed (General Director of the Petroleum Exploration and Production Board, P.E.B.B- Aden), Mr. Abdella M. Ali (Exploration Manager, P.E.P.B.) Mr. H. Fadel (Database Center Manager, P.E.B.P), Mr. Jamil Al-Ariki (Administration & Govt. Relations Manager, C.P.Y.L. (Canadian Petroleum Yemen Limited)), Mr. Mohammed A. Rageh (Exploration Coordinator. C.P,Y.L.), Engs.,: M. Maheob, S. Al-Khalaki, T. Bakhdar, A. Rashad, A. Ahmed, S. Khamis and Miss. Wafa & Fatimah Khamis for their help during various stages of my research and who have helpped make this work possible. I have to thank Miss. Zhang Xin Rong, for her help and support, Mr. Ma Xiao Gang, Mr. Wang Qinjun for notations of computer programs and also due to Mrss. Li Mingxiao for redrawing the suggested Yemeni stratigraphic coloumn using Corel Drew. Special thanks go to Mr. Bian Quicheng for help and encouragement; to other staff members of Foreighn Affairs Office of Earth Science College of Jilin University, especially to Mrs., Fan Xuirong and Mrs. Jiang Yan. Someone said that "many people will walk in & out of your life, but only true friends will leave footprints in your heart." I'm so glad that all above metioned people lift theirs in mine. 6
  • 7. INTRODUCTION My interest in the Yemeni Geology started on my first investigation practise in Al-Kharj area Marib Al-Jawf Shabwah Basin (former South Yemen) during my master degree studies in Moscow (Russia) on 1987. And also during my work in the Adeni Branch of the Ministry of Oil and Mineral Resource (the Petroleum Exploration and Production Board) from 1992 to 1999. Science my assignment to follow up office and field exploration works for a number of blocks granted to foreign companies working in most of Yemeni territory, particularly blocks granted to companies worked, work and still work in the north northeastern, eastern and south southeastern part of the Republic of Yemem. I did my best to use the huge material, data and the whole pervious work done by others and by me during my work in the area as an interance on a new look to the Yemeni geology as a whole. Important Notice: The north northeastern, eastern and south southeastern contains about more than 75% of Yemeni sedimentary cover and occupies an area of more than 40.000 square kilometers (It’s included the Yemen Sector of Rub al Khali basin in the north and northeastern part of Yemen). THESIS TOPICS I found that one of the most famous and more complex topics problem, which face any researcher who would like to make any kind of geological studies on the Yemeni Geology are: 1. How to introduce the previous and present geological activities work in the area? (Yemen have a very rich Geologicl Research History 1852 - till Today) 2. How to solve the chronic problem releted to the Yemeni Lithostratigraphic Units and Nomenclature? (There are many companies worked, work and stil work in different areas in Yemen and every company have its Lithostratigraphic column, units and nomenclature in accordance to their study to the area in which they worked, work) 3. How to image the phanerozoic geology of the north northeastern, eastern and south southeastern parts of Yemen in a 3D model, based on mapping the interested area by different geological maps from the basement till the surface? Two New Patent Methods: 1. What is the best effective method, which make it easy to do a 3D Geological Model? 7
  • 8. 2. Which way we must use to make it easy to unsderstand the whole earth history evolution? (and in a short time) NATURE OF THE PROBLEM Prompted largely by this interest, my research plan was concentrated on its achievement on the following important point: 1. Study and examination of all primary information connected with the subject from various sources. 2. Sorting of this information in accordance with its importance. 3. Making a number of tables, charts, maps and 3D Models. 4. Checking of all data and making necessary tests on them. 5. Follow-up of the historical development on the formation of the geological structures through the making of varying three dimentional models from the bottom of the interested area to its surface. * Personal Activities (Patents) 1. It is known that to make a geological section, a coorellation or a three dimension geological model using the traditional drawing manual way methods or a computer software programm methods means a spicial preparation. What is the new method and the more effective way, which make it easy to do the above mentioned subjects and cheap? 2. It is known also that it is difficult to fix in other people minds the whole earth history evolution by using the traditional ways . So, which way we must use to make it easy to unsderstand the whole earth history evolution in a short time? AIM OF THIS STUDY The study was aimed at the problems outlined in the previous two sections: This Ph.D. thesis is the first investigation work thesis study, which aims to: 1. Help understanding of the pervious and present geological activities in the Republic of Yemen. 2. Help understanding of the Yemeni Lithostratigraphic Units (The Yemeni Stratgraphic Nomenclature) by introducing the first tabel on the whole Yemeni Lithostratigraphic Units. 3. Help understanding of the Yemeni Phanerozoic geology by studing the eastern part as a whole, 4. Introduce two new projected methods (Patents). 8
  • 9. CONTENTS ABSTRACT i ACKNOWLEDGMENTS v INTRODUCTION vi THESIS TOPICS NATURE OF THE PROBLEM vii AIM OF THIS STUDY CONTENTS viii LIST OF FIGURES xii LIST OF TABLES xviii CHAPTER 1: THE REPUBLIC OF YEMEN GENERAL INTRODUCTION 1 1.1 THE GEOLOGICAL RESEARCH HISTORY WORK (G.R.H.W.) OF THE REPUBLIC OF YEMEN (1852- UNTIL TODAY), (A NEW PART WITH NEW TERMS, NAMES, CLASSIFICATION AND DIVISION) 2 1.2 COUNTRY OVERVIEW 15 1.3 ECONOMIC OVERVIEW 18 1.4 ENERGY OVERVIEW 21 1.5 ENVIRONMENTAL OVERVIEW 21 1.6 OIL AND GAS INDUSTRIES 22 1.7 GEOGRAPHY 22 1.8 DRAINAGE 25 1.9 CLIMATE 26 1.10 VEGETATION 27 1.11 ACCESSIBILITY 29 9
  • 10. CHAPTER 2: REGIONAL GEOLOGY OF YEMEN 30 2.1. INTRODUCTION 31 2.2 PRECAMPRIAN 37 2.3 PHANEROZOIC 44 2.3.1 EVOLUTION OF YEMEN ’s PHANEROZOIC SEDIMENTARY BASIN 46 2.3.1.1 PALEOZOIC BASINS 47 2.3.1.2 MESOZOIC BASINS 48 2.3.1.3 TERTIARY BASINS 49 2.3.2 DEVELOPMENT OF PHANEROZOIC BASIN AND PLATFORM COVER 50 2.3.2.1 INFRA-CAMBRIAN/ PALEOZOIC 50 2.3.2.2 MESOZOIC 55 2.3.2.3 CENOZOIC 59 CHAPTER 3: GEOLOGY OF YEMEN 61 3.1 INTRODUCTION 62 3.2 ARCHEAN-PROTEROZOIC BASEMENT 63 3.3 PHANEROZOIC SEDIMENTARY ROCKS 69 3.4 STRUCTURE AND TECTONICS OF YEMEN 95 3.5 SURFACE UPLIFT AND DENUDATION 100 3.5.1 SEDIMENTOLOGICAL EVIDENCE FOR THE UPLIFT HISTORY 100 3.5.2 FISSION TRACK ANALYSIS OF THE EXHUMATION HISTORY 101 3.5.3 GEOMORPHOLOGICAL EVIDENCE FOR UPLIFT AND DENODATION HISTORY 101 3.6 GEOLOGICAL HISTORY 105 CHAPTER 4: THE WHOLE YEMEN LITHOSTRATIGRAPHIC UNITS AND NOMENCLATURE TABLE 107 4.1 INTRODUCTION 108 10
  • 11. 4.2 STRATIGRAPHIC PRINCIPLES AND PROCEDURES: A SUMMARY 108 4.3 DEVELOPMENT OF THE LITHOSTRATIGRAPHIC UNITS AND NOMENCLATURE IN YEMEN 111 4.4 THE FIRST ELECTRONIC AND ATTRIBUTE TABLE ON THE WHOLE YEMENI LITHOSTRATIGRAPHIC UNITS AND NOMENCLATURE 122 CHAPTER 5: SUMMARY OF STRATIGRAPHY 148 5.1 INTRODUCTION 149 5.2 BASEMENT 153 5.3 PHANEROZOIC COVER 153 5.3.1 PALEOZOIC 153 5.3.2 MESOZOIC 154 5.3.2.1 TRIASSIC 157 5.3.2.2 JURASSIC 157 5.3.2.3 CRETACEOUS COASTAL AREA 159 5.3.2.4 CRETACEOUS: HADRAMUT AREA 161 5.3.3 CENOZOIC 162 5.3.3.1 PALEOCENE-MIDDLE EOCENE 164 5.3.3.2 OLIGOCENE-MIOCENE 165 5.3.3.3 PLIOCENE – RECENT 165 5.3.4 IGNEOUS ROCKS 165 CHAPTER 6: PHANEROZOIC SIDIMENTARY SEQUENCE SUBDIVISION /STRATIGRAPHIC/SEDIMENTOLOGIC ANALYSIS 226 6.1 INTRODUCTION 227 11
  • 12. 6.2 PALEOZOIC 228 6.2.1 Lithology 228 6.2.2 Source rock/reservoir characteristics 230 6.3 TRIASSIC (?) – JURASSIC 230 6.3.1 Lithology 230 6.3.2 Source rock/reservoir characteristics 231 6.4 CRETACEOUS 232 6.4.1 Lithology 232 6.4.2 Source rock/reservoir characteristics 232 6.5 PALEOCENE – MIDDLE EOCENE 233 6.5.1 Lithology 233 6.5.2 Source rock/reservoir characteristics 233 6.6 OLIGOCENE / MIOCENE – RECENT 234 6.6.1 Lithology 234 6.6.2 Source rock/reservoir characteristics 235 CHAPTER 7: PRESENCE OF THE WHOLE EOCENE AND TRIASSIC ON THE YEMENI ISLAND OF SOCOTRA 236 7.1 INTRODUCTION 237 7.2 THE GEOLOGICAL RESEARCH HISTORY WORK OF SOCOTRA ISLAND 237 7.3 GEOLOGY OF SOCOTRA ISLAND 238 7.4 STRATIGRAPHIC SUMMARY OF SAMAH-1A 239 7.5 OIL AND GAS PREDICTION 240 CHAPTER 8: OIL AND GAS PROSPECT IN THE YEMENI SECTOR OF RUB AL-KHALI BASIN 242 8.1 INTRODUCTION 243 12
  • 13. 8.2 THE YEMENI SECTOR OF RUB AL KHALI BASIN GEOLOGICAL RESEARCH HISTORY WORK 244 8.3 THE RUB AL-KHALI SAND DESERT 246 8.4 THE YEMENI SECTOR OF RUB AL-KHALI BASIN 247 8.5. SATELLITE IMAGES INTERPRETATION 247 8.6 NEW LOOK TO THE AREA 248 8.7 CONCLUSION 249 8.8 RECOMMENDATION 249 CHAPTER 9: THE (3D.Y.G.M. – TIN FOR ALL): THE THREE DIMENSION YEMENI GEOLOGICAL MODEL – TIN FOR ALL 277 CHAPTER 10: THE (T.G.T.C.): AL-TOHAITA (SER YA KAOS) GEOLOGICAL TIME CLOCK 283 CHAPTER 11: DISCUSSION, CONCLUSION AND RECOMMENDATION 287 11.1 Discussion 288 11.2 Conclusion 289 11.3 Recommendation 290 REFERENCES 292 LIST OF FIGURES Fig. (1.1) The Republic of Yemen Geological Research History Work New Division. 4 13
  • 14. Fig. (1.2) Show the way must be used by authors to write about the most famous geologists and their most famous works during the first stage of the Geological Research History Work of Yemen 4 Fig. (1.3) Show the way must be used by authors to write about the famous scientific expedition and their famous works during the first stage of the Geological Research History Work of Yemen 5 Fig. (1.4) Show the way must be used by authors to write about the most famous companies and their most famous works during the first stage of the Geological Research History Work of Yemen 5 Fig. (1.5) Show the way must be used by authors to write about the most famous geologists and their most famous works during the second stage of the Geological Research History Work of Yemen 6 Fig. (1.6) Show the way must be used by authors to write about the famous scientific expedition and their famous works during the second stage of the Geological Research History Work of Yemen 6 Fig. (1.7) Show the way must be used by authors to write about the most famous companies and their most famous works during the second stage of the Geological Research History Work of Yemen 7 Fig. (1.8) Show the way must be used by authors to write about the most famous geologists and their most famous works during the third stage of the Geological Research History Work of Yemen 7 Fig. (1.9) Show the way must be used by authors to write about the famous scientific expedition and their famous works during the third stage of the Geological Research History Work of Yemen 8 Fig. (1.10) Show the way must be used by authors to write about the most famous companies and their most famous works during the third stage of the Geological Research History Work of Yemen 8 Fig. (1.11) Show the way must be used by authors to write about the most famous geologists and their most famous works during the fourth stage of the Geological Research History Work of Yemen 9 Fig. (1.12) Show the way must be used by authors to write about the famous scientific expeditionand and their famous works during the fourth stage of the Geological Research History Work of Yemen 9 Fig. (1.13) Show the way must be used by authors to write about the most famous companies and their most famous works during the fourth stage of the Geological Research History Work of Yemen 10 Fig (1.14), Fig. (1.15) and Fig. (1.16) Show different forms of the New Classification and Division to the Geological Research History Work of the Republic of Yemen. 11 Fig. (1.17) The official Map of the Republic of Yemen 15 14
  • 15. Fig. (1.18): The Republic of Yemen (Location Map) 15 Fig. (1.19): Yemen Population Density Map 16 Fig. (1.20): Yemen Administrative Divisions Map 17 Fig. (1.21) Crude Oil Export and Destinations (Nedham, M. Darsi, 2000) 19 Fig. (1.22): Yemen Economic Activity Map 20 Fig. (1.23: The Organization Chart of the Ministry of Oil and Mineral Resources in Yemen 23 Fig. (1.24) Geographic Map of the Republic of Yemen 24 Fig. (1.25) The Yemeni Drainage System 25 Fig. (1.26): Yemen Land Use Map 28 Fig. (1.27) Show the locations of the major roadways, ports, etc. in Yemen, as well as the governorate boundaries. 29 Fig. (2.1) Index map showing location of Fig. (2.1A) and (2.1B) in the regional context. 32 Fig. (2.1A) Yemen: Location Map (Western Sheet) 33 Fig. (2.1B) Yemen: Location Map (Eastern Sheet) 34 Fig. (2.2) The Concession Map of the Republic of Yemen 35 Fig. (2.3) Sedimentary Basin Map of the Republic of Yemen (Nedham M. Darsi, 2001; after As-Saruri and Baraba, 1995) 38 Fig. (2.4) Regional structural framework 39 Fig. (2.5) Structural elements outline map with principal highs/uplifts and basins. 42 Fig. (2.6A) Selected well correlation across different sedimentary basins and highs (Western Part) 52 Fig. (2.6B) Selected well correlation across different sedimentary basins and highs (Eastern Part) 53 Fig. (3.1) Geographic map of Yemen 63 Fig. (3.2) Index to geological mapping in Yemen 65 Fig. (3.3) Precambrian basement geology of Yemen (Menzies, et al., 1994; after A – Northwest Yemen (Geomin 1985); B – Northeast Yemen (Christmann et al., 1984); C – Sana’a – Al-Bayda (Kruck et al., 1991); D: Yaffa (Strojexport. 1988); 15
  • 16. E – Lawder – Wafid – Beyhan (Lobunets et al., 1988); and F – Habban-Al-Mukalla (Scharamm et al., 1986)). 66 Fig. (3.4) Correlation of Precambrian units in northern Yemen (Menzies, et al., 1994; after GEOMIN, 1985 and Chrismann et al., 1984) 68 Fig. (3.5) Geology of Yemen modified by Menzies, et al., 1994; after Robertson Group (1992) 68 Fig. (3.6) Stratigraphy of Yemen (By Menzies, et al., 1994; after Beydoun, 1964) 70 Fig. (3.7) Stratigraphy column of the Akbra Shale, Yemen (Davison et al., 1994) 71 Fig. (3.8) Stratigraphy column of the Kohlan Sandstone, Yemen (Davison et al., 1994) 74 Fig. (3.9) Major Jurassic palaeographic and tectonic features of Yemen 76 Fig. (3.10) Nomenclature pertinent to Jurassic stratigraphy across Yemen from the Bayda area (Al-Thour, 1992), the graben shoulder northwest of Dhamar-Marib (Kruck et al., 1991), the Ramlat As Sabatayn graben (Schlumberger, 1992) and the eastern platform (Beydoun and Greenwood, 1968; Haitham and Nani, 1990). 77 Fig. (3.11) Stratigraphy of the Amran Limestone from Al-Ayen area, Yemen (By Menzies, et al., 1994; after Al-Thour, 1993) 78 Fig. (3.12) Stratigraphy of the Tawilah Group at Jabal Marmer, Al Ghiras, Yemen (Al-Subbary and Nichols 1991; Al-Subbary et al., 1993) 82 Fig. (3.13) Cretaceous-Tertiary paleogeography of Yemen (Al-Subbary and Nichols 1991 and 1993 unpublished data) 84 Fig. (3.14) Stratigraphy of the Tawilah Group to Yemen Volcanics transition, Yemen (Al-Kadasi and Minzies, 1993 unpublished data) 90 Fig. (3.15) Histogram of K-Ar Ages for the Yemen Volcanic Group (Al-Kadasi et al., 1992; Al-Kadasi, Rundle and Menzies, 1993, unpublished data) 93 16
  • 17. Fig. (3.16) Stratigraphy of the Yemen Volcanics from Al Qanawis to San’a, Yemen (Baker and Menzies, 1993, unpublished data) 94 Fig. (3.17) Tectonic feature of Yemen (McClay 1993, unpublished data) 97 Fig. (3.18) Distribution of apatite fission track ages from Yemen. Apatites were extracted from outcroping gneissic basement and Paleozoic-Mesozoic sediments (Yeland et al., 1994, Yeland et al., 1994 unpublished data) 98 Fig. (3.19) Annual precipitation and temperature distribution in western Yemen (Menzies, et al., 1994; after Dequin, 1976) 103 Fig. (3.20) Geomorphological profile across western Yemen (Menzies, et al., 1994; after Davison et al., 1994). 104 Fig. (4.1) Yemen: Historical development of selected Jurassic stratigraphic nomenclature schemes. 117 Fig. (4.2) Yemen: Historical development of selected cretaceous stratigraphic nomenclature schemes. 118 Fig. (5.1) Simplified geological map of the southwestern part of the Arabian Peninsula. 151 Fig. (5.2) Major tectono-stratigraphic elements of the former south Yemen. 152 Fig. (5.3A) Thickness Map for the Youngest Sediment or Formation (Layer No. 1)166 Fig. (5.3B) 3D Model for the Youngest Sediment or Formation ( Layer No. 1 ) 167 Fig. (5.4A) Thickness Map for Sarar Formation ( Layer No. 2 ) 168 Fig. (5.4B) 3D Model for Sarar Formation ( Layer No. 2 ) 169 Fig. (5.5A) Thickness Map for Taqah/Hami Formation ( Layer No. 3 ) 170 Fig. (5.5B) 3D Model for Taqah/Hami Formation ( Layer No. 3 ) 171 Fig. (5.6A) Thickness Map for Ghaidah Formation ( Layer No. 4 ) 172 Fig. (5.6B) 3D Model for Ghaidah Formation ( Layer No. 4 ) 173 Fig. (5.7A) Thickness Map for Habshyia Formation ( Layer No. 5 ) 174 Fig. (5.7B) 3D Model for Habshyia Formation ( Layer No. 5 ) 175 Fig. (5.8A) Thickness Map for Rus Formation ( Layer No. 6 ) 176 Fig. (5.8B) 3D Model for Rus Formation ( Layer No. 6 ) 177 Fig. (5.9A) Thickness Map for Jiza Formation ( Layer No. 7 ) 178 Fig. (5.9B) 3D Model for Jiza Formation ( Layer No. 7 ) 179 17
  • 18. Fig. (5.10A) Thickness Map for Umm Er Radhuma Formation ( Layer No. 8 ) 180 Fig. (5.10B) 3D Model for Umm Er Radhuma Formation ( Layer No. 8 ) 181 Fig. (5.11A) Thickness Map for Simsima/Sharwayn Formation ( Layer No. 9 ) 182 Fig. (5.11B) 3D Model for Simsima/Sharwayn Formation ( Layer No. 9 ) 183 Fig. (5.12A) Thickness Map for Fiqah Formation ( Layer No. 10 ) 184 Fig. (5.12B) 3D Model for Fiqah Formation ( Layer No. 10 ) 185 Fig. (5.13A) Thickness Map for Mukalla Formation ( Layer No. 11 ) 186 Fig. (5.13B) 3D Model for Mukalla Formation ( Layer No. 11 ) 187 Fig. (5.14A) Thickness Map for Sufla Member ( Layer No. 12 ) 188 Fig. (5.14B) 3D Model for Sufla Member ( Layer No. 12 ) 189 Fig. (5.15A) Thickness Map for Fartaq Formation ( Layer No. 13 ) 190 Fig. (5.15B) 3D Model for Fartaq Formation ( Layer No. 13 ) 191 Fig. (5.16A) Thickness Map for Harshiyat Formation ( Layer No. 14 ) 192 Fig. (5.16B) 3D Model for Harshiyat Formation ( Layer No. 14 ) 193 Fig. (5.17A) Thickness Map for Wasia Group ( Layer No. 15 ) 194 Fig. (5.17B) 3D Model for Wasia Group ( Layer No. 15 ) 195 Fig. (5.18A) Thickness Map for Qishn Formation ( Layer No. 16 ) 196 Fig. (5.18B) 3D Model for Qishn Formation ( Layer No. 16 ) 197 Fig. (5.19A) Thickness Map for Qishn Carbonate Member ( Layer No. 17 ) 198 Fig. (5.19B) 3D Model for Qishn Carbonate Member ( Layer No. 17 ) 199 Fig. (5.20A) Thickness Map for Qishn Clastic Member ( Layer No. 18 ) 200 Fig. (5.20B) 3D Model for Qishn Clastic Member ( Layer No. 18 ) 201 Fig. (5.21A) Thickness Map for Biyad ( Layer No. 19 ) 202 Fig. (5.21B) 3D Model for Biyad ( Layer No. 19 ) 203 Fig. (5.22A) Thickness Map for Sa'ar Formation ( Layer No. 20 ) 204 Fig. (5.22B) 3D Model for Sa'ar Formation ( Layer No. 20 ) 205 Fig. (5.23A) Thickness Map for Nayfa Formation ( Layer No. 21 ) 206 18
  • 19. Fig. (5.23B) 3D Model for Nayfa Formation ( Layer No. 21 ) 207 Fig. (5.24A) Thickness Map for Sab'atayn Formation ( Layer No. 22 ) 208 Fig. (5.24B) 3D Model for Sab'atayn Formation ( Layer No. 22 ) 209 Fig. (5.25A) Thickness Map for Lam Member ( Layer No. 23 ) 210 Fig. (5.25B) 3D Model for Lam Member ( Layer No. 23 ) 211 Fig. (5.26A) Thickness Map for Madbi Formation ( Layer No. 24 ) 212 Fig. (5.26B) 3D Model for Madbi Formation ( Layer No. 24 ) 213 Fig. (5.27A) Thickness Map for Shuqra Formation ( Layer No. 25 ) 214 Fig. (5.27B) 3D Model for Shuqra Formation ( Layer No. 25 ) 215 Fig. (5.28A) 3D Model for Kohlan Formation ( Layer No. 26 ) 216 Fig. (5.28B) 3D Model for Kohlan Formation ( Layer No. 26 ) 217 Fig. (5.29A) Thickness Map for (Permian – Triassic?) Formation( Layer No. 27 ) 218 Fig. (5.29B) 3D Model for (Permian – Triassic?) Formation ( Layer No. 27 ) 219 Fig. (5.30A) Thickness Map for the (Devonian - Carboniferous) Formation ( Layer No. 28 ) 220 Fig. (5.30B) 3D Model for the (Devonian - Carboniferous) Formation ( Layer No. 28 ) 221 Fig. (5.31A) Thickness Map for the Oldest Sediment or Formation (Cambrian (?) – Ordovician – Lower Silurian) ( Layer No. 29) 222 Fig. (5.31B) 3D Model for the Oldest Sediment or Formation (Cambrian (?) – Ordovician – Lower Silurian) ( Layer No. 29) 223 Fig. (5.32A) Thickness Map for the drilled parts of the Basement ( Layer No.30 ) 224 Fig. (5.32B) 3D Model for the drilled parts of the Basement ( Layer No.30 ) 225 Fig. (7.1): Socotra Island (Republic of Yemen) 241 Fig. (7.2): Socotra Island (Republic of Yemen); 1886 241 Fig. (8.1) Satellite Images No.1: Arabian Sea (N19.25-E58.71) 250 Fig. (8.2) Satellite Images No.2: Arabian Sea (N19.15-E58.77) 251 Fig. (8.3) Satellite Images No.3: Yemen 14, Sanaw (N18.17-E50.78) 252 Fig. (8.4) Satellite Images No.4: Yemen 15, (N17.51-E51.23) 253 19
  • 20. Fig. (8.5) Satellite Images No.5: Yemen 16, (N17.38-E51.31) 254 Fig. (8.6) Satellite Images No.6: Yemen 17, (N18.46-E51.05) 255 Fig. (8.7) Satellite Images No.7: Yemen 18, Wadi Rakhawt (N17.79-E51.50) 256 Fig. (8.8) Satellite Images No.8: Yemen 19, (N17.69-E51.57) 257 Fig. (8.9) Satellite Images No.9: Yemen 20, Desert (N17.69-E50.28) 258 Fig. (8.10) Satellite Images No.10: Yemen 1, Desert (Latitude Longitude at Image center N17.11-E50.67) 259 Fig. (8.11) Satellite Images No.11 Yemen 2, Desert (N16.66-E50.96) 260 Fig. (8.12) Satellite Images No.12: Yemen 3, Al Mujaza’ah (N17.28-E49.65) 261 Fig. (8.13) Satellite Images No.13: Yemen 4, (N16.36-E50.08) 262 Fig. (8.14) Satellite Images No.14: Yemen 5, (N16.52-E50.16) 263 Fig. (8.15) Satellite Images No.15: Border Saudi Arabia-Yemen (N18.57-E49.43) 264 Fig. (8.16) Satellite Images No.16: Yemen 6, (N18.22-E49.67) 265 Fig. (8.17) Satellite Images No.17: Yemen 7, (N17.90-E49.89) 266 Fig. (8.18) Satellite Images No.18: Yemen 8, (N17.58-E50.12) 267 Fig. (8.19) Satellite Images No.19: Yemen 9, (N17.25-E50.36) 268 Fig. (8.20) Satellite Images No.20: Yemen 10, Jabal Mahrat (N16.93-E50.57) 269 Fig. (8.21) Satellite Images No.21: Yemen 11, Jabal Mahrat (N16.77-E50.67) 270 Fig. (8.22) Satellite Images No.22: Border Saudi Arabia-Yemen (N18.64-E51.36) 271 Fig. (8.23) Satellite Images No.23: Yemen 12, (N17.97-E51.81) 272 Fig. (8.24) Satellite Images No.24: Yemen 13, (N17.85-E51.88) 273 Fig. (8.25) Interpreted satellite Images No.6: Yemen 17, (N18.46-E51.05) 274 Fig. (8.26) Satellite Images No.25: show first projected point 275 Fig. (8.27) Satellite Images No.26: show second projected point 276 Fig. (9.1): The 3DYGM-For All Tin; (Outer View) 279 Fig. (9.2): The 3DYGM-For All Tin; (Inner View) 280 Fig. (9.3): The 3DYGM-For All Tin; (A Column Construction) 281 20
  • 21. Fig. (9.4): Using the 3DYGM-For All Tin to make a Geological Well Section 282 Fig. (10.1): Al-Tohaita Geological Time Clock (TGTC); (Type No.1) 285 Fig. (10.2): Al-Tohaita Geological Time Clock (TGTC); (Type No.2) 286 21
  • 22. LIST OF TABLES Table. (1.1) Crude Oil Export and Destinations 18 Table. (3.1) Summary of geological mapping in the Republic of Yemen. 64 Table. (4.1) The Republic of Yemen Lithostratigraphic Units and Nomenclature Table 124 (Attaced) Table (5.1) Infra-Cambrian to (?) Lower Cambrian Basement Units 153 Table (5.2) Paleozoic Units 154 Table (5.3) Mesozoic Units 155 Table (5.3A) Cretaceous: Coastal Area Units 159 Table (5.4) Cenozoic Units 163 . 22
  • 23. CHAPTER 1: 1 THE REPUBLIC OF YEMEN GENERAL GEOLOGY 2 1.1 THE GEOLOGICAL RESEARCH HISTORY WORK (G.R.H.W.) OF THE REPUBLIC OF YEMEN (1852- UNTIL TODAY), (A NEW PART WITH NEW TERMS, NAMES, CLASSIFICATION AND DIVISION) 1.1.1 INTRODUCTION 1.1.2 NEW CLASSIFICATION AND DIVISION 3 STEP N0. 1 FIRST STAGE SECOND STAGE THIRD STAGE FOURTH STAGE STEP N0. 2 4 HOW TO WRITE ABOUT THE FIRST STAGE AS A WHOLE STEP N0. 3 6 HOW TO WRITE ABOUT THE SECOND STAGE AS A WHOLE STEP N0. 4 7 HOW TO WRITE ABOUT THE THIRD STAGE AS A WHOLE STEP N0. 5 9 HOW TO WRITE ABOUT THE FOURTH STAGE AS A WHOLE STEP N0. 6 11 HOW TO WRITE ABOUT THE FOUR STAGES AS A WHOLE 1.2 COUNTRY OVERVIEW 15 1.3 ECONOMIC OVERVIEW 18 1.4 ENERGY OVERVIEW 21 1.5 ENVIRONMENTAL OVERVIEW 21 1.6 OIL AND GAS INDUSTRIES 22 23
  • 24. 1.7 GEOGRAPHY 22 1.8 DRAINAGE 25 1.9 CLIMATE 26 1.10 VEGETATION 27 1.11 ACCESSIBILITY 29 24
  • 25. CHAPTER 1 THE REPUBLIC OF YEMEN GENERAL GEOLOGY 1.1 THE GEOLOGICAL RESEARCH HISTORY WORK IN THE REPUBLIC OF YEMEN DURING THE PERIOD FROM 1852 UNTIL TODAY (A NEW PART WITH A NEW TERMS, NEW NAMES, NEW CLASSIFICATION AND DIVISION) 1.1.1 INTRODUCTION This part of my Ph.D. thesis is one of the most important parts of my work. It is a new part done by me. This new part I called it the Geological Research History Work of Yemen (G.R.H.W.). It is a new part with a new look to the previous and present geological activities in the area. This new part must be added to any kind of geological works about Yemen in the future. It must be written after the introduction directly as an independent part of the general part (Chapter 1). It is known that it is so difficult for any persons to do the following kind of works: First, to read about previous and present activities in Yemen. Second, to speak about previous and present activities in Yemen. Third, to keep in mind informations related to previous and present activities in Yemen. Fourth, to teach student in schools institutes collages and universities about previous and present activities in Yemen. Fifth, to introduce to others previous and present activities in Yemen. If you, read any books about Yemeni geology with an aim to know more about the previous and present geological activities in Yemen, you will notice the following most important notices: 1. Most of authors in their scientific works about Yemen like to write about perivious and present activities in Yemen as a part of their introduction. 2. Different authors have different ideas and different ways to write about perivious and present geological activities in Yemen, because they know very nice, that Yemen have a very rich geological research history. So in their introduction about the Yemeni geology, they cannot wrote about perivious and present geological activities as a whole. So different group of authors likes to write about different branches of pervious and present activities in Yemen. This make it so difficult to have a conclusion about pervious and present geological activities in Yemen. 25
  • 26. 2 Yemen has a very rich and long geological research history work aged 150 years. During those 150 years, many Geologists, Expedition and different Companies worked, work and still work in Yemen. In my opinion, it is time now to stop writing about perivious and present activities in Yemen as a part of any introduction on the Yemeni Geology, which means more difficulties in the future. So to solve this problem I decided to write about perivious and present geological activities in Yemen as an independent part which I called it, the Geological Research History Work (G.R.H.W.). The Term (G.R.H.W.): means the Geological Research History Work. It is a new term, which first time used by me, when I published my first, second, third scientific papers on the Geological Research History Work in the Republic of Yemen in the Yemen Times News paper and also my fourth paper on the same subject in World Geology, China. The term G.R.H.W. means the Geological Research History Work (The Pervious and the Present activities) as a whole, in accordance with my new classification and division to the G.R.H.W. in Yemen. 1.1.2 NEW CLASSIFICATION AND DIVISION It is known that rich geological research history work in any country is largely depended upon written documents, whereas the G.R.H.W. must be inferred from the careful study. Based on variably detailed information of hundreds publications references. I found that the best way to make the Geological Research History Work in the Republic of Yemen (The New Part) to be easy to read, to write, to speak, to keep in mind, to teach and to introduce to others is to do the following new steps: Step No.1: I decided to divide the geological research history work in the Republic of Yemen as a whole to four stages: (See, Fig. (1.1)) First Stage: 1852-1901. I gave it two new names: First name: The First Systematic Geological Observation Stage. Second name: Carter’s Stage. Second Stage: 1902-1946. I gave it the following name: The Hinterland Studies Stage. 26
  • 27. Third Stage: 1947-1967. I gave it two new names: First name: The First systematic more detailed Stratigraphic and Geological Studies Stage. Second name: Beydoun, Z.R., 's Stage. Fourth Stage: 1968 - until Today. I gave it the following name: The Yemeni Geologists Stage Fig. (1.1) The Geological Research History Work in the Republic of Yemen First Stage: 1852- Second Stage: Third Stage: 1947-1967. Fourth Stage: 1901. 1902-1946. 1968 - Until Today. I gave it two new names: I gave it two new I gave it the I gave it the following names: following name: (1) The First systematic more name: (1) The First detailed Stratigraphic and Systematic The Hinterland Geological Studies Stage. The Yemeni Geological Studies Stage. Geologists Stage Observation (2) Beydoun, Z.R., 's Stage. Stage. 27
  • 28. Step No.2: 1. To write about the First Stage (The First Systematic Geological Observation Stage or Carter’s Stage) as whole, authors must write about the following activities and use the equivalent new terms. F IR S T S T A G E T H E F IR S T S Y S T E M A T IC G E O L O G IC A L O B S E R V A T IO N S T A G E O R C A R T E R ’s S T A G . 1 .T H E M O S T F A M O U S G E O L O G I S T S A N D T H E I R M O S T F A M O S W O R K IN Y E M E N D U R IN G T H E F IR S T S T A G E 1.1. To write about the 1 .1 . Y E M E N I G E O L O G I S T S 1 .2 . A R A B G E O L O G I S T S Most Famous Geologists 1 .3 . F O R E I G H N G E O L O G I S T S and their most famous N O T E (1 ): IF A N Y O N E W A N T T O W R IT E A B O U T T H E F IR S T S T A G E O F T H E G E O L O G IC A L R E S E A R C H H I S T O R Y W O R K I N Y E M E N ,H E M U S T W R I T E A B O U T T H E A B O V E M E T I O N E D STEPS A S A W H O LE. Work (M.F.G.& W. 1) during the first stage As whole, authors must Work with Fig. (1.2) Fig. (1.2) F IR S T S T A G E T H E F IR S T S Y S T E M A T IC G E O L O G IC A L O B S E R V A T IO N S T A G E O R C A R T E R ’s S T A G . 2 .T H E M O S T F A M O U S S C IE N T IF IC E X P E D IT IO N A N D T H E IR M O S T F A M O S W O R K IN Y E M E N D U R IN G T H E F IR S T S T A G E 2 .1 . Y E M E N I S C IE N T IF IC E X P E D IT IO N 2 .2 . A R A B S C IE N T IF IC E X P E D IT IO N 1.2. To write about the 2 .3 . F O R E IG H N S C IE N T IF IC E X P E D IT IO N N O T E ( 1 ): IF A N Y O N E W A N T T O W R I T E A B O U T T H E F IR S T S T A G E O F T H E G E O L O G IC A L Famous Scientific R E S E A R C H H I S T O R Y W O R K I N T H E R E P U B L I C O F Y E M E N , H E M U S T W R IT E A B O U T T H E A B O V E M E T IO N E D S T E P S A S A W H O L E Expeditionand their famous Work (F.S.E.& W. 1) during the first stage as whole authors must 28
  • 29. Work with Fig. (1.3) Fig. (1.3) F IR S T S T A G E T H E F IR S T S Y S T E M A T IC G E O L O G IC A L O B S E R V A T IO N S T A G E O R C A R T E R ’s S T A G . 3 . T H E M O S T F A M O U S C O M P A N IE S A N D T H E IR M O S T F A M O S W O R K IN Y E M E N D U R IN G T H E F IR S T S T A G E 1.3. To write about the 3 .1 . Y E M E N I C O M P A N IE S 3 .2 . A R A B C O M P A N IE S Most Famous Companies 3 .3 . F O R E IG N C O M P A N IE S and their most famous Work H IS T O R Y O F E X P L O R A T IO N , P R O D U C T IO N , ? A C T IV IT IE S N O T E (1 ): IF A N Y O N E W A N T T O W R IT E A B O U T T H E F IR S T S T A G E O F T H E G E O L O G IC A L R E S E A R C H H IS T O R Y W O R K IN T H E R E P U B L IC O F Y E M E N , H E M U S T W R IT E A B O U T T H E (M.F.C.& W. 1) during the A B O V E M E T IO N E D S T E P S A S A W H O L E first stage as whole, authors must Work with Fig. (1.4) Fig. (1.4) 29
  • 30. Step No.3: 2. To write about the Second Stage (The Hinterland Studies Stage) as whole, authors must write about the following activities and use the equivalent new terms. SEC O N D STA G E T H E H IN T E R L A N D S T U D IE S S T A G E . 2.1. To write about the 1 .T H E M O S T F A M O U S G E O L O G I S T S A N D T H E I R M O S T F A M O S W O R K IN Y E M E N D U R IN G T H E S E C O N D S T A G E Most Famous Geologists 1 .1 . Y E M E N I G E O L O G I S T S 1 .2 . A R A B G E O L O G I S T S and their most famous 1 .3 . F O R E I G H N G E O L O G I S T S Work (M.F.G.& W. 2) N O T E (1 ): IF A N Y O N E W A N T T O W R IT E A B O U T T H E S E C O N D S T A G E O F T H E G E O L O G I C A L R E S E A R C H H I S T O R Y W O R K I N Y E M E N ,H E M U S T W R I T E A B O U T T H E A B O V E M E T IO N E D STEPS AS A W H OLE. during the second stage As whole, authors must Work with Fig. (1.5) Fig. (1.5) Fig. (1.5) SEC O N D STAG E T H E H IN T E R L A N D S T U D IE S S T A G E 2 .T H E M O S T F A M O U S S C IE N T IF IC E X P E D IT IO N A N D T H E IR M O S T F A M O S W O R K IN Y E M E N D U R IN G T H E S E C O N D S T A G E 2 .1 . Y E M E N I S C I E N T I F I C E X P E D I T I O N 2 .2 . A R A B S C I E N T I F I C E X P E D I T I O N 30 2 .3 . F O R E I G H N S C I E N T I F I C E X P E D I T I O N
  • 31. 2.2. To write about the Famous Scientific Expedition and their famous Work (F.S.E.& W. 2) during the second stage as whole authors must Work with Fig. (1.6) Fig. (1.6) 2.3. To write about the Most Famous Companies and their most famous Work (M.F.C.& W. 2) during the second stage as whole, authors must Work with Fig. (1.7) Fig. (1.7) 31
  • 32. Step No.4: 3. To write about the Third Stage (The First systematic more detailed Stratigraphic and Geological Studies Stage or Beydoun, Z.R., 's Stage) as whole, authors must write about the following activities and use the equivalent new terms. T H IR D S T A G E T H E F IR S T S Y S T E M A T IC M O R E D E T A IL E D S T R A T IG R A P H IC A N D 3.1. To write about the G E O L O G I C A L S T U D I E S S T A G E O R B E Y D O U N , Z .R ., 's S T A G E . Most Famous Geologists 1 .T H E M O S T F A M O U S G E O L O G I S T S A N D T H E I R M O S T F A M O S W O R K IN Y E M E N D U R IN G T H E T H IR D S T A G E and their most famous 1 .1 . Y E M E N I G E O L O G I S T S 1 .2 . A R A B G E O L O G I S T S Work (M.F.G.& W. 3) 1 .3 . F O R E I G H N G E O L O G I S T S during the first stage N O T E (1 ): IF A N Y O N E W A N T T O W R IT E A B O U T T H E T H IR D S T A G E O F T H E G E O L O G IC A L R E S E A R C H H I S T O R Y W O R K I N Y E M E N ,H E M U S T W R I T E A B O U T T H E A B O V E M E T I O N E D STEPS AS A W H OLE As whole, authors must Work with Fig. (1.8) Fig. (1.8) T H IR D STAG E T H E F IR S T S Y S T E M A T IC M O R E D E T A IL E D S T R A T IG R A P H IC A N D G E O L O G IC A L S T U D I E S S T A G E O R B E Y D O U N , Z . R . , 's S T A G E . 2 .T H E M O S T F A M O U S S C I E N T I F I C E X P E D I T I O N A N D T H E I R M O S T F A M O S W O R K IN Y E M E N D U R IN G T H E T H IR D S T A G E 2 .1 . Y E M E N I S C I E N T I F I C E X P E D I T I O N 2 .2 . A R A B S C I E N T I F I C E X P E D I T I O N 32 2 .3 . F O R E I G H N S C I E N T I F I C E X P E D I T I O N
  • 33. 3.2. To write about the Famous Scientific Expeditionand their famous Work (F.S.E.& W. 3) during the third stage as whole authors must Work with Fig. (1.9) Fig. (1.9) 3.3. To write about the Most Famous Companies TH IRD STAG E and their most famous Work THE FIRST SYSTEM ATIC M ORE DETAILED STRATIGRAPHIC AND GEOLOGICAL STUDIES STAGE OR BEYDOUN, Z.R., 's STAGE. (M.F.C.& W. 3) during the 3. THE M OST FAM OUS COM PANIES AND THEIR M OST FAM OS W ORK IN YEM EN DURING THE THIRD STAGE third stage as whole, 3.1. YEM ENI COM PANIES authors must Work with 3.2. ARAB COM PANIES 3.3. FOREIGN COM PANIES Fig. (1.10) HISTORY OF EXPLORATION, PRODUCTION, ? ACTIVITIES NOTE (1): IF ANYONE W ANT TO W RITE ABOUT THE THIRD STAGE OF THE GEOLOGICAL RESEARCH HISTORY W ORK IN THE REPUBLIC OF YEM EN, HE M UST W RITE ABOUT THE ABOVE M ETIONED STEPS AS A W HOLE. Fig. (1.10) 33
  • 34. Step No. 5: 4. To write about the Fourth Stage (The Yemeni Geologists Stage) as whole, authors must write about the following activities and use the equivalent new terms. FOURTH STAGE THE YEMENI GEOLOGISTS STAGE 1.THE MOST FAMOUS GEOLOGISTS AND THEIR MOST 4.1. To write about the FAMOS WORK IN YEMEN DURING THE FOURTH STAGE 1.1. YEMENI GEOLOGISTS Most Famous Geologists 1.2. ARAB GEOLOGISTS and their most famous 1.3. FOREIGHN GEOLOGISTS Work (M.F.G.& W. 4) NOTE (1): IF ANYONE WANT TO WRITE ABOUT THE FOURTH STAGE OF THE GEOLOGICAL RESEARCH HISTORY WORK IN YEMEN,HE MUST WRITE ABOUT THE ABOVE METIONED STEPS AS A WHOLE. during the Fourth Stage As whole, authors must Work with Fig. (1.11) Fig. (1.11) 4.2. To write about the Famous Scientific FOURTH STAGE Expeditionand their THE YEMENI GEOLOGISTS STAGE 2.THE MOST FAMOUS SCIENTIFIC EXPEDITION AND THEIR MOST FAMOS WORK IN YEMEN DURING THE FOURTH STAGE famous Work (F.S.E.& W. 4) 2.1. YEMENI SCIENTIFIC EXPEDITION during the fourth stage as 2.2. ARAB SCIENTIFIC EXPEDITION whole authors must 2.3. FOREIGHN SCIENTIFIC EXPEDITION NOTE (1): IF ANYONE WANT TO WRITE ABOUT THE FOURTH STAGE OF THE GEOLOGICAL Work with Fig. (1.12) RESEARCH HISTORY WORK IN THE REPUBLIC OF YEMEN, HE MUST WRITE ABOUT THE ABOVE METIONED STEPS AS A WHOLE. Fig. (1.12) 34
  • 35. Fig. (1.12) 4.3. To write about the Most Famous Companies and their most famous Work (M.F.C.& W. 4) during the fourth stage as whole, authors must Work with Fig. (1.13) Fig. (1.13) 35
  • 36. Step No. 6: To write about the Four Stages as whole, authors must write about the following activities and use the equivalent new terms. (See Figs. (1.14), (1.15) and (1.16)) The Geological Research History Work in the Republic of Yemen First Stage: Second Stage: Third Stage: 1947-1967. Fourth Stage: 1852-1901. 1902-1946. 1968 - until I gave it two new names: Today. I gave it two I gave it the new names: following (1) The First systematic I gave it the (1) The First name: more detailed following Systematic Stratigraphic and name: Geological The Geological Studies Stage. Observation Hinterland The Yemeni Stage. Studies Stage. (2) Beydoun, Z.R., 's Geologists (2) Carter’s Stage. Stage Stage. M F M M F M M F M M F M F S F F S F F S F F S F G E C G E C G E C G E C & & & & & & & & & & & & W W W W W W W W W W W W 1 1 1 2 2 2 3 3 3 4 4 4 The Geological The Geological The Geological Research History Research History Research History Work Work of the Most Work of the Most of the most Famous Famous Companies Famous Geologists Scientific and their most famous and their most Expeditions and their Work during the Four famous Work during most famous Work Stages as a whole the Four Stages as a during the Four Stages whole as a whole Fig. (1.14) 11 36
  • 37. The Geological Research History Work in the Republic of Yemen First Stage: Second Stage: Third Stage: 1947-1967. Fourth Stage: 1852-1901. 1902-1946. 1968 - until I gave it two new names: Today. I gave it two I gave it the new names: following (1) The First systematic I gave it the (1) The First name: more detailed following Systematic Stratigraphic and name: Geological The Geological Studies Stage. Observation Hinterland The Yemeni Stage. Studies Stage. (2) Beydoun, Z.R., 's Geologists (2) Carter’s Stage. Stage Stage. M F M M F M M F M M F M F S F F S F F S F F S F G E C G E C G E C G E C & & & & & & & & & & & & W W W W W W W W W W W W 1 1 1 2 2 2 3 3 3 4 4 4 M M M M F F F F M M M M F F F F S S S S F F F F G G G G E E E E C G C C & & & & & & & & & & & & W W W W W W W W W W W W 1 2 3 4 1 2 3 4 1 2 3 4 The Most Famous The Scientific A Restudy on Exploration Activities Geologists Expeditions Companies and their Groups and their and their Geological Geological Geological Production Activities Research History Research History Research Work during the Work during the History Work Four Stages Four Stages during the Four Stages (I, II, III, IV) (I, II, III, IV) (I, II, III, IV) Fig. (1.15) 37
  • 38. The Geological Research History Work in the Republic of Yemen (M.F.G.&W1) (F.S.E.&W1) (M.F.C.&W1) Most Famous Famous Scientific Most Famous Geologists and Expedition Companies and their most famous and their famous their most famous Work during the Work during the First Work during the First Stage Stage First Stage M M M F F F M M M F F F Y A F F F F Y A F S S S Y A F G G G E E E C C C & & & & & & & & & W W W W W W W w W 1 1 1 1 1 1 1 1 1 M M M M F F F F M M M M F F F F S S S S F F F F G G G G E E E E C G C C & & & & & & & & & & & & W W W W W W W W W W W W 1 2 3 4 1 2 3 4 1 2 3 4 The Most Famous The Scientific A Restudy on Exploration Activities Geologists Expeditions Companies and and their Groups and their their Geological Production Activities Geological Geological Research Research History Research History History Work Work during the Work during the during the Four Four Stages Four Stages Stages (I, II, III, IV) (I, II, III, IV) (I, II, III, IV) Fig. (1.16) 38
  • 39. IMPORTANT NOTICE: To prove that we in Yemen are highly in need for such new part, with the new classification and division, and to show how it is easy now to use the new classification and division to write about the geological research history work of Yemen in parts or as whole. I published six scientific papers (the first five scientific papers published on the first and most famous newspaper in Yemen, Yemen Times and one in China on World Geology). (Nedham, M.Darsi (2000, 2001)) On my first published papers on the geological research history work of the Republic of Yemen I used my new classification and division. I used it not just to prove how it is easy now to write about our G.R.H.W in parts or as whole, but also to discuss and to answer one of the most important questions. Who are the most famous geologists, who play a great role in the geological research history work of the Republic of Yemen during the period from 1852 until Today? (Please, see the attached references). 1.2. COUNTRY OVERVIEW 1. Location: Southwest corners of the Arabian Peninsula, the Republic of Yemen is bordered in the northwest, north and northeast by Saudi Arabia, in the east by Oman and in the south by the Gulf of Aden. To the west lies the Red Sea. The islands of Soqotra, Abdul Kuri, Darsa, Perim, … and Kamaran in the Arabian Sea and southern Red Sea are also part of the Republic of Yemen. (Fig. (1.17), (1.18)) Fig. (1.17): The Official Map of the Republic of Yemen 39
  • 40. Fig. (1.18): The Republic of Yemen (Location Map) 2. Area: 527,790 sq. kilometers (203,730 sq. miles); approximately the size of Wyoming and Colorado 3. Independence: May 22, 1990 (reunification) 4. Population: 16,483,000 (1997). 5. Population density: 30.7 per sq km. (Fig. (1.19)) 40
  • 41. Fig. (1.19): Yemen Population Density Map 6. Capital: Sana'a dates back to the first century with Population: 926,595 (1993). 7. Major Cities: Sanaa (capital), Aden, Al Hudaydah, and Taizz. (Fig. (1.20)) 41
  • 42. Fig. (1.20): Yemen Administrative Divisions Map 8. Language: Arabic. English is spoken in some urban areas. 9. Religion: Islam. 10. Time: GMT +3. 11. Economic & Commercial Capital: Aden. Population: 400,783 (1993). 12. Government: Republic. Head of State: President Ali Abdallah Saleh since 1990. Head of Government: Prime Abdulkader Ba-Gammal since 2001. 13. Electricity: 220/230 volts AC, 50Hz. 14. Communications: Country. Code: 967. Outgoing international code: 00. Press: English-language publications include The Yemen Times (weekly) and The Yemen Observer (monthly). Arabic dailies include Ash-Sharara and Al-Thaura. 15. The metric system is in general use throughout the country; however, some English weight and measures are also used. Note: The information contained in these Ph.D. theses is the best available as of July 1999 and can change. 42
  • 43. 1.3. ECONOMIC OVERVIEW In 1998, Yemen's real gross domestic product (GDP) growth was 2.7%, and it is expected to climb to 4.2% in 1999, based mainly on the recovery in oil prices. Meanwhile, inflation has been reduced, but not completely brought under control. After reaching a high of 71% in 1995, inflation is projected at 10% for 1999. Income from oil sales account for approximately 40% of Yemen's total revenues and is the country's main source of foreign currency. 1. Currency: Yemeni Rial (YR), the current rate of exchange is about U.S.$1.00=YR 160. 2. Gross Domestic Product (GDP) - purchasing power parity exchange rate (1998E): $5.6 billion 3. Major Trading Partners: China, Japan, Saudi Arabia, Singapore, South Korea, United Arab Emirates, United States 4. Major Export Products: Crude oil, cotton, coffee, hides, vegetables, dried and salted fish 5. Major Import Products: textiles and other manufactured consumer goods, petroleum products, sugar, grain, flour, other foodstuffs, cement, machinery, chemicals. (Table (1.1), Figs. (1.21), (1.22)) Table. (1.1) Crude Oil Export and Destinations COUNTRY QUANTITY PRICE PERCENTAGE (%) (Barrels) USD China 13138862 2.77E+08 27.88 % Korea 10259311 2.17E+08 21.77 % Japan 6,518,963 1.27E+08 13.83 % Thailand 6,212,318 1.23E+08 13.18 % Brazil 2,801,413 61592458 5.94 % South Africa 2,120,637 43176359 4.50 % Singapore 1,677,337 31532088 3.56 % Egypt 1,350,000 24560550 2.86 % Aden/Yemen 1,199,829 25934369 2.55 % Italy 799,518 15625668 1.70 % France 572,209 12756827 1.21 % Kenya 483,000 9,984,407 1.03 % Total 47,133,397 9.68E+08 100 % 43
  • 44. Fig. (1.21) Crude Oil Export and Destinations (Nedham, M. Darsi, 2000) 44
  • 45. Fig. (1.22): Yemen Economic Activity Map 45
  • 46. 1.4. ENERGY OVERVIEW 1. Proven Oil Reserves (1/1/99): 4 billion barrels 2. Oil Production (1998E): 385,000 barrels per day (bbl/d) 3. Oil Consumption (1998E): 69,000 bbl/d 4. Net Oil Exports (1998E): 316,000 bbl/d 5. Crude Oil Refining Capacity (1/1/99): 120,000 bbl/d 6. Natural Gas Reserves (1/1/99): 16.9 trillion cubic feet (Tcf) 7. Electric Generating Capacity (1/1/97): 810 megawatts 8. Electricity Generation (1997E): 2.1 billion kilowatt-hours 1.5. ENVIRONMENTAL OVERVIEW 1. Total Energy Consumption (1998E): 0.15 quadrillion Btu* (0.04% of world total energy consumption). 2. Energy-Related Carbon Emissions (1998E): 3.0 million metric tons of carbon (0.05% of world carbon emissions). 3. Per Capita Energy Consumption (1998E): 10.6 million Btu (vs. U.S. value of 350.7 million Btu). 4. Per Capita Carbon Emissions (1998E): 0.2 metric tons of carbon (vs. U.S. value of 5.5 metric tons of carbon). 5. Energy Intensity (1997E): 11,300 Btu/ $1990 (vs U.S. value of 13,900 Btu/ $1990)** 6. Carbon Intensity (1997E): 0.22 metric tons of carbon/thousand $1990 (vs U.S. value of 0.21 metric tons/thousand $1990)**. 7. Sectoral Share of Energy Consumption (1997E): Transportation (70.4%), Residential (18.8%), and Industrial (10.9%). 8. Sectoral Share of Carbon Emissions (1997E): Transportation (69.9%), Industrial (10.1%), and Residential (19.8%). 9. Fuel Share of Energy Consumption (1997E): Oil (100.0%). 10. Fuel Share of Carbon Emissions (1998E): Oil (100.0%). 11. Renewable Energy Consumption (1997E): 1.6 trillion Btu* 12. Number of People per Motor Vehicle (1997): 29.4 (vs. U.S. value of 1.3). 13. Status in Climate Change Negotiations: Non-Annex I country under the United 14. Nations Framework Convention on Climate Change (ratified February 21st, 1996). Not a signatory to the Kyoto Protocol 46
  • 47. 15. Major Environmental Issues: Very limited natural fresh water resources; inadequate supplies of potable water; overgrazing; soil erosion; desertification 16. Major International Environmental Agreements: A party to Conventions on Biodiversity, Climate Change, Desertification, Environmental Modification, Hazardous Wastes, Law of the Sea, Nuclear Test Ban and Ozone Layer Protection * The total energy consumption statistic includes petroleum, dry natural gas, coal, net hydro, nuclear, geothermal, solar and wind electric power. The renewable energy consumption statistic is based on International Energy Agency (IEA) data and includes hydropower, solar, wind, tide, geothermal, solid biomass and animal products, biomass gas and liquids, industrial and municipal wastes. Sectoral shares of energy consumption and carbon emissions are also based on IEA data. **GDP based on EIA International Energy Annual 1998 1.6. OIL AND GAS INDUSTRIES 1. Organizations: Yemen Petroleum Company (YPC) - production and refining; General Corporation for Oil and Mineral Resources (GCOMR) - investment and holding company; Yemen Refining Company (YRC) - refining; General Department of Crude Oil Marketing (GDCOM) - handles government shares of exports; Yemen Exploration and Production Company (YEPC) – contracts. (See the Organization Chart of the Ministry of Oil and Mineral Resources in Yemen. (See Fig. (1.23): The Organization Chart of the Ministry of Oil and Mineral Resources in Yemen). 2. Major oilfields: Alif, Asaad Al-Kamil, Camaal, and Azal. 3. Major Foreign Company Involvement: British Gas, Canadian Occidental, First Calgary Petroleum, Hunt Oil, Kerr- McGee, Nimir Petroleum, Total, TransGlobe Energy, and Yukong. 4. Major Refineries (Capacity): Aden (110,000 bbl/d), Marib (10,000 bbl/d) 5. Major Ports: Aden, Hisn an Nushaymah, Al Khalf, Mocha, Nishtun, Ra's Isa, Ra's Kathib, and Salif. Major Pipelines: Marib-Ra's Isa Pipeline (pipeline between the Marib fields and the deep-sea port of Ra's Isa on the Red Sea), Shabwa-Rudhum Pipeline (pipeline linking the Shabwa fields to the Rudhum terminal on the Gulf of Aden at Hisn an Nushaymah). 47
  • 48. 1.7. GEOGRAPHY Yemen is predominantly mountainous, supporting terraced agriculture. The Hadramaut is a range of high mountains in the centre of the country. Highlands rise steeply in central Yemen, ranging in height from approximately 200m (656ft) to the 4000m (13,123ft) peak of Jabal Nabi Shoveb. In contrast is Tihama, a flat semi-desert coastal plain to the west, 50-100km (30-60 miles) wide. Surface water flows down from the mountains through the valleys during the rainy season and the area is cultivated for cotton and grain. In the east the mountains drop away to the Rub al-Khali or 'Empty Quarter' of the Arabian Peninsula, a vast sea of sand. The arid coastal plains are fringed with sandy beaches. Fig. (1.24) Fig. (1.23): The Organization Chart of the Ministry of Oil and Mineral Resources in Yemen 48
  • 49. Fig. (1.24) Geographic Map of the Republic of Yemen 1.8. DRAINAGE With only three exceptions, the drainage system of Yemen consists of dry water courses or wadis which flow only in times of heavy rains during flash floods. Some wadis are very deeply cut, with sides more than 300 meters in elevation above the water course; others are wider with less steep sides; and still others are broad and flat. Wadi Tuban, north of Aden, and Wadi Hajr, east of Balhaf, are perennial from, their headwaters in the coastal mountains to the sea. Parts of Wadi Masila are perennial; though not, however, reaching the sea. (Fig. (1.25)) The Yemen drainage system can be divided into three groups: 1.Coastal wadis 2. Wadis flowing to the Rub al Khali sand desert 49
  • 50. 3. The Hadramaut-Masila and Wadi Jeza systems Fig. (1.25) The Yemeni Drainage System 1.Coastal wadis: With some exceptions, flow in general northwest – southeast and northeast-southwest directions, turning more southerly and westerly near the coast; most are less than 100 kilometers long, rising in the Coastal Mountain belt or the Southern Plateau, and south of the axis of the South Hadramaut uplift. Most of these wadis are torrential, with steep gradients; they are not easily navigable by motor transport. 2. Wadis flowing to the Rub al Khali sand desert: Are usually long, and they trend in a north-northeast direction. They are often much shallower than those flowing into Wadi Hadramaut. Their heads are in the vicinity of the axis of the North Hadramaut uplift, which also is the highest part of the Northern Plateau. In the west, they cut through Paleocene limestone to Cretaceous sandstone in places, but eastward they expose only Eocene beds. 3. The Hadramaut-Masila and Wadi Jeza systems: Collect drainage from the greater part of both the Southern and Northern Plateaus. Except for the lower part of Wadi Masila, thet occupy roughly the structural depression between the North and South Hadramaut uplifts. Wadi Hadramaut, at its western end, is really a wide basin, some 50 kilometers in the width, that forms parts of the Western Plain and the Jaww Kudayf plain with the Ramlat Sabatayn dune area in between. The wadi narrows rapidly eastward until it becomes only two to three kilometers across, its canyon walls being the scarps of the Northern the 50
  • 51. Southern Plateaus. The tributary wadis entering Wadi Hadramaut-Masila are usually long and deeply cut canyons with a gentle gradient; they are generally accessible to vehicular travel. The canyons, like the Wadi Hadramaut-Masila, are cut in Paleocene limestone with Cretaceous rocks exposed in places. The cliffs forming the sides of the wadis are 300 or more meters in height, but become lower eastwards. The heads of the tributaries rise near the axis of the South and North Hadramaut uplift, and the water collects in the Hadramaut depression, whence it flows east; and later, as Wadi Masila, cuts obliquely across the eastern plunge of the South Hadramaut uplift to reach the sea. The Wadi Hadramaut depression continues eastward across low-relief country to take in the Wadi Jeza system. This forms the gathering drainage for wadis from the eastern parts of the North and South Plateaus, the water flowing east to Qamar Bay. The Jeza basin is one of more gentle relief than that of Wadi Hadramaut, and the tributary wadis are less deeply incised. Wadis flowing to the north in the Jaww Kudayf plain and southward in the Western Plain die out in the Ramlat Sabatayn sand desert, but in the subsurface their flood waters join the Wadi Hadramaut – Masila system. 1.9. CLIMATE The Yemeni Climate in detail: The Republic of Yemen is affected by monsoon winds of the Indian Ocean region.the monsoon blow in two seasons: the winter monsoon from October to April, blowing from the southeast or east-southeast; and the summer monsoon which blows steadily from the west or southwest during June through August. During the winter monsoon, winds are moderate; and, although rough seas are frequent, but rain is sporadic, often occurring only as localized showers. The end of the winter monsoon may, at times, bring heavy rain over a great part of the area, but such heavy rain is the exception rather than the rule. During the summer, monsoon winds are violent and the seas very rough; gusts may reach 100kilometers per hour, but again only sporadic rain falls. Although the chances of widespread rain are greater during the winter monsoon, two or three years may pass between worthwhile rains. Along the coast, the recorded average annual rainfall is about 50 millimeters, while in the interior, an annual average as much as 400 millimeters has been recorded. During the late winter months of 1982 and 1983, however, exceptional conditions prevailed throughout the region: torrential rains of the “once in a hundred years” variety occurred throughout the country with resultant flood waters which swept away bridges and roads, collapsed dwellings, and flooded vast 51
  • 52. agricultural areas. These episodes were apparently related to the violent weather experienced throughout Asia and Europe during these periods. The hottest months in Yemen are May to September, with a peak in June and July when temperature above 38OC (100OF) are frequent. Temperature of 54Oc (130OF) are reached in some localities. During the winter months, low temperature below 0OC (32OF) are reached in the interior, but it seldom falls below 15O (60OF) along the coast. The months May and September are those between the turn of the monsoons and experience very humidity and heat, with little or no breeze. In the interior, at various times during the winter, cold dust-laden winds blow in the summer. Sandstorms are relativly frequent, and dust devils and mirages are common. Dusty conditions are general in the summer, and visibility between June and September is generally poor. A Conclusion on the Yemeni Climate: The climate varies according to altitude. The coastal plain is hot and dusty throughout most of the year. The highlands are warm in summer and during winter, from October to March, nights can be very cold in the mountains. Annual rainfall is extremely low and temperatures, particularly in summer, are very high. The most pleasant time is from October to April. 1.10. Vegetation The vegetation of the Republic of Yemen is on the whole sparse, except in wadi beds, where bunch grass, camel thorn, acacia, tamarisk, and ilb grow; the mountain areas and the plateaus are mainly barren. In the main wadis and along parts of the coast where water is available for irrigation, or where floodwaters are utilized, millet and other grains, cotton, tobacco, vegetabls, oil and date palms, bananas, papayas, and citrus are cultivated. Concentrations of deciduous trees are found in a few places, and occasional frankincense and myrrh plants may be found in many parts of the region. Fig. (1.26) 52
  • 53. Fig. (1.26): Yemen Land Use Map 1.11. Accessibility Yemen is important to world energy markets because of its oil and natural gas resources as well as its strategic location at the Bab el-Mandab strait linking the Red Sea and the Gulf of Aden, one of the world's most active shipping lanes. In 1954, and by 1964 only London, Liverpool, and New York surpassed port of Aden. Most of Yemeni roads are asphalt is the principal avenue of transportation in Yemen. Principal highways lead from San’a south to the north part of Aden and from San’a north to Saudi Arabia border. Traffic proceeds on the right-hand side of the road, with speed limits of 30 km/hr in the cities, and 60 km/hr on open roads. The country is linked to San’a by regular air services from Aden, Taiz, Hodeidah, Albuq, Sayun, Riyan, Alghaydah, Ataq, Socotra, and a few other towns, and flights can be arranged to more than fourteen scattered small airstrips. Alyamania is the national airline. Fig. (1.27) 53
  • 54. Fig. (1.27) Show the locations of the major roadways, ports, etc. in Yemen, as well as the governorate boundaries. 54
  • 55. CHAPTER 2: REGIONAL GEOLOGY OF YEMEN 30 2.1. INTRODUCTION 31 2.2 PRECAMPRIAN 37 2.3 PHANEROZOIC 44 2.3.1 EVOLUTION OF YEMEN ’s PHANEROZOIC SEDIMENTARY BASIN 46 2.3.1.1 PALEOZOIC BASINS 47 2.3.1.2 MESOZOIC BASINS 48 2.3.1.3 TERTIARY BASINS 49 2.3.2 DEVELOPMENT OF PHANEROZOIC BASIN AND PLATFORM COVER 50 2.3.2.2 INFRA-CAMBRIAN/ PALEOZOIC 50 2.3.2.2 MESOZOIC 55 2.3.2.3 CENOZOIC 59 55
  • 56. CHAPTER 2 REGIONAL GEOLOGY OF YEMEN Based on my personal research work on the Yemeni Geology during my work in the Adeni Branch of Ministry of Oil and Mineral Resource, (the Petroleum Exploration and Production Board), for 8 years. And my research studies on my Ph.D. Thesis on the same direction and with another main aim to solve the chronic problems related to the Yemeni Lithostratigraphic Units and Nomenclature. I made the first table on the whole Yemeni Lithostratigraphic Units and Nomenclature (See Table. (4.1); attached to this study). It is the first electronic attribute table, which I am going to introduce it later on this thesis as a real solution and a correct entranceway to solve the above-mentioned mater. Although my table is an easy to read and to understand, but it is so important and necessary to introduce the great previous activities done by different people on writing the Regional, Local Geology of Yemen. Especially the last great job and effort did by Beydoun, Z.R. and a group of most famous Yemeni geologists (Beydoun et al., 1998). And all of this due to variably detailed information of hundreds publications done on the Yemeni geology. (See the attached references). IMPORTANT NOTICE (1): I would like to drew the reader of my thesis attention on the following most important mater that one of the most important problem which make it so difficult to write on the Yemeni Geology as a whole is that the whole Yemen was divided to blocks. (Figs. (2.1), (2.1A), (2.1B) and (2.2)) In my opinion dividing Yemen as a whole to blocks is the real reason which, lead to the development of company-centered informal stratigraphic nomenclature schemes whose principal objective was to facilitate operations within the individual company’s concession area rather than facilitating scientific research and any ultimate communication in journals. So to solve this question, we must scientifically divide just the sedimentary basins in Yemen to blocks in accordance to their categorisation not the whole country to blocks (We must always choose the most effective scientific methods of work to draw a bright future for our grandchildren). 56
  • 57. 2.1 INTRODUCTION It is known that the Republic of Yemen geologically occupies the southern edge of the Arabian Shield, formed in Precambrian times from a tangled complex of ancient rocks. Though the shield has acted a rigid landmass since the beginning of 31 Cambrian time, consolidation was a long time in coming. Included within the basement complex are great belts of sedimentary rocks – now contorted, intruded, and metamorphosed – that record the growth and the decay of former mountain systems. Through the areas of Precambrian time, the shielded presumably was subjected several times to down warping, sedimentation, orogeny, injection by plutonic rocks, and leveling before becoming immobile – a complex, but little- known structural history comparable to that of other shields and former geosynclinal areas. In the western part of the Republic of Yemen, the Precambrian basement supports a relatively high, substantially faulted Plateau capped in part by patches of flat-lying Jurassic, Cretaceous, and Tertiary sedimentary rocks. After solidification and mature peneplanation, the Arabian Shield was tilted slightly to the northeast toward the ancestral Tethys trough. As subsidence continued, shallow seas advanced across the leveled surface of crystalline rocks, burying it beneath thin sheets of almost flat – lying sediment. This belt of low – dipping, relatively undisturbed beds form the stable region structural province – the Arabian Shelf. 57
  • 58. Fig. (2.1) Index map showing location of Fig. (2.1A) and (2.1B) in the regional context. Fig. (2.1A) Yemen: Location Map (Western Sheet) 58
  • 59. Fig. (2.1B) Yemen: Location Map (Eastern Sheet) Fig. (2.2) The Concession Map of the Republic of Yemen 59
  • 60. The eastern part of the Republic of Yemen as a part of my Ph.D. Thesis topics overlies this shelf. It should be kept in mind, however, that the shelf differs from the exposed part of the Arabian Shield only in possessing a thin sedimentary cover. The Yemeni sector of Rub al Khali basin is the main area, which took a lot of care by me. It is clear for all researchers and people who interested in this field that this area is the first area, which attracted foreign companies to work in Yemen in the 70th. (It is known that the most famous and biggest oil discoveries all over the World located in Rub al Khali basin). I took care of that area especially because the Yemeni sector of Rub al Khali basin is a part of the southern margin of that basin (Fig. (2.3)). One of the most important things I have done after a short time I reached China is that my scientific paper on the Oil and Gas Prospect in the Yemeni sector of Rub al Khali basin with Professor Wang Xi Kui. Although the first previous exploration activities by foreign companies working in that area stopped early by this or that reason. And just on the last two years started again by Canadian Petroleum Ltd., whom I highly appreciated their cooperation with me during my research visit to the area after the publication of my paper and during their seismic survey in the area. The Yemeni sector of Rub al Khali basin as northern extension of the shelf area consists of a broad belt of Paleozoic, Mesozoic, and Cenozoic strata whose dip into the interior Rub al Khali basin is so slight and uniform as to be almost imperceptible. This homocline, which extend on vast areas of Saudi Arabia and Oman, dips north under the Rub al Khali sand sea from a line in the Republic of Yemen to south of the southern edge of the sands. From Cambrian time on, vast epicontinental seas moved back and forth across the lower part of the stable basement core, depositing a comparatively thin succession of almost flat – lying strata. The epicontinental seas were in turn flanked on the north and east by a great sedimentary basin – the Tethyan trough – occupying a relatively constant area in Turkey, northern Iraq, and southwestern Iran. This trough remained a negative feature throughout most of Paleozoic and Mesozoic time while many thousands of meters of sediment were deposited. Destruction of the ancient seaway began in the late Cretaceous with orogenic movement recorded from Turkey through Iran and extending into Oman. The climax came, however, in the 60
  • 61. late Tertiary (Alpine orogeny) when rocks from the Zagros-Taurus chain of mountains. It was during this period that the great rift – fault systems of Africa and the Red Sea areas, including the Gulf of Aden, also began to take on their present form (although movement on these faults may have started somewhat earlier). Until recently, the Arabian Shield was a projection of the shield of Africa, but is now separated from it by the Red Sea – Gulf of Aden rifting. Fig. (2.4) 2.2 PRECAMBRIAN The Precambrian geology is still in its early beginning. And what different groups, have achieved so far in different Precambrian terranes, varies considerably in its in-depth understanding, with no reliable correlation of common units between different terranes. Investigations have been carried out during general geological mapping and/or for mineral investigations; the groups involved included governmental technical assistance agencies of Romanian, French and U.S. teams in former North Yemen and East German and Soviet teams in former South Yemen. Problems of inconsistency in nomenclature used by these different groups have resulted in some confused regarding the proper understanding the geological evolution of Yemen during the Precambrian. These problems is partly resolved by a comprehensive review carried out by Vesolov (1990) resulting in a broad regional stratigraphic frame-work for the Precambrian basement and the first recognition of Archean rocks in the Arabian Peninsula. A more local attempt at such a framework for the Late Proterozoic-Early Paleozoic units of former South Yemen, covering the west of the Al-Mukalla region, was carried out by Krentz et al. (1990). As-Saruri and Wiefel (1997, in press) meanwhile synthesised data relating to the basement structural provinces of the central region of former South Yemen between Al-Mahfid and Mukalla embodying the data obtained by the various German mapping groups. And attempted to reconstruct the evolutionary phases of structural provinces and of cratonisation of the region during the Proterozoic into the start of the Phanerozoic. 61
  • 62. More regional investigations utilising published data and new field observations by groups of academic researchers which included geochronological dating and extension of detailed data from the Arabian Shield in Saudi Arabia obtained by such researchers as Stacey and Agar (1985), Agar (1985), White (1985), Agar et al. (1992) and others. And into Yemen has identified several gneissic and island arc terranes, some of which can be correlated with the eastern margin of the Arabian Shield in Saudi Arabia and with Northern Somalia (Ba-Bttat et al., 1989; Stoeser et al., 1991; Whitehouse et al., 1993; Windley et al., 1996). These include Late Archean to Proterozoic gneissic terranes and Pan-African island arc terranes and suture zones; Yemen thus provide the link between the arc collage of the Arabian Shield and the gneissic Mozambique belt of East Africa. Although, on the last new Lexicon of stratigraphy Precambrian stratigraphy (sensu stricto) has been left out of the nomenclature description. Nevertheless a synopsis of the geological evolution of Precambrian crustal rocks is deemed useful as it provides the geotectonic and stratigraphic foundation on which the Phanerozoic platform cover was laid down. 62
  • 63. Fig. (2.3) Sedimentary Basin Map of the Republic of Yemen (Nedham, M.Darsi, 2001; after As-Saruri and Baraba, 1995) 63
  • 64. Fig. (2.4) Regional structural framework; Total Aden (Yemen), 1990 The first systematic account of the Precambrian basement rocks of Yemen was that by Greenwood and Bleackley (1967) which incorporated the Late Proterozoic/Infra-Cambrian nomenclature. Descriptions and generalised investigations made by Beydoun (1964, 1966) on Precambrian rocks outcropping in the western part of the Eastern Aden Protectorate (Shabwa and SW Hadhramawt Provinces of present Yemen). This nomenclature was then formalised in the first edition of the International Lexicon of Stratigraphy for part of Yemen (the former Aden Protectorate and Dhufar in SW Oman) by Beydoun and Greenwood (1968). With this, an overall but generalised account of the geological evolution of this region for the Precambrian was 64
  • 65. included which discussed units and complexes in terms of relative age backed by a few sparse absolute age determinations. The presence of older gneiss attributed to an ‘‘earlier’’ Precambrian was recognised; this subsequently underwent probable planation as suggested by the presence of derived pebbles. This was followed by the ‘’late’’ Precambrian Aden Metamorphic Group (including the Garish and Thaniyah Groups of Beydoun, 1964, 1966), with syntectonic granite intrusions approximately coeval with the main phase of regional metamorphism and associated pegmatite’s and feldspathic bands. A phase of inters tectonic igneous activity then followed. This involved both intrusive and extrusive (including the Tha’lab Group of Beydoun op. cit., with its wide spectrum of volcanic ranging from olivine basalt’s, andesites, rhyolites, rare trachytes and great quantities of pyroclastics). Dyke swarms were intruded mainly during the late phase of this activity and were seemingly terminated by extension and graben formation immediately prior to or contemporaneously with the start of another episode of planation. Into these extensional grabens, sedimentaries of the Ghabar Group (Beydoun, 1964, 1966; Beydoun and Greenwood, 1968) were laid down during the latest Precambrian to earliest Phanerozoic time, which were then folded, cleaned and slightly metamorphosed, possibly during a Najd-equivalent tectonic event involving strike-slip motion and transpression/transtension. Post-tectonic granitic intrusions with crosscutting contacts and thermal aureoles terminate the basement cratonisation history. These have been age-dated as Cambrian (Snelling in Greenwood and Bleakly, 1967; in Beydoun and Greenwood, 1968). Other age dating on the older basement by Snelling (op. cit.) suggest that all the basement units of the former Aden Protectorate region are Proterozoic (with the possible exception of the ‘’older gneiss’’), with the Ghabar Group and succeeding undeformed granitic plutons being of latest Proterozoic to Infra-Cambrian-Cambrian age. Beydoun (1970, 1982) correlated these basement units with similar ones in Dhufar, northern Somalia (former British Somali land) and Saudi Arabia (as documented by Brown and Jackson, 1980) and others at that time. Gass (1981), Al-Shanti and Gass (1983), Stoeser and Camp (1985), Stacey and Agar (1985), Agar et al. (1992) and others, have in consequence of recent additional mapping activity and age dating in the 65
  • 66. region. Divided the Arabian Shield of Saudi Arabia into a number of accreted arc terranes and inter arc suture zones based on composition and geochronological dating. These were reviewed by Beydoun (1988), who suggested a similar Pan-African accretionary evolutionary history for the Yemen Precambrian but speculated on the possibility that contiguous Somalia at that time could form the northern part of the older but remobilised Mozambique basement belt to the south. Then the ongoing new mapping work in Yemen by the various international groups indicated above has recently culminated in a synthesis paper embodying earlier published work as well as new field traverses, sampling and radiometric age dating across the Central or Al- Mahfid uplift (Windley et al., 1996). In this (and partly in some earlier work), seven terranes plus the Nabitah Suture were recognised in the basement of Yemen, which are, from west to east: Fig. (2.5) 1. The An-Nimas terrane (Geomin, 1985, cited in GSMEB, 1994), constituting the continuation into Yemen of the Asir terrane of Saudi Arabia and composed there of volcanic arcs and other plateaus and basins. 2. The Al-Qarah terrane, which is the continuation into Yemen of the Nabitah orogenic belt of Saudi Arabia with similar petrogenic affinities to that accreted arc terrane (Geomin, 1985, cited in GSMEB, 1994). 3. The Nabitah Suture, which extends to Hajjah in NW Yemen Fig. (2.5), where a 30 x 5 km minimum size aphiolite is present and the suture zone is stitched by post-tectonic granites (Windley et al., 1996). 4. The Najran terrane (Christman et al., 1984, cited in GSMEB, 1994), which constitutes the Afif terrane of Saudi Arabia as identified in Yemen, where it consists of monotonous orthogneisses intercalated with arc type pillow basalts, andesites and rhyolites. This terrane is tentatively interpreted as a Pan-African Andean type continental margin in so far as the arc has a continental basement (Windley et al., 1996). 66
  • 67. 5. The Abas terrane with two main component: orthogneisses which are migmatised, and metamorphosed supra-crustal rocks (the Rada Group) (Windley et al., 1996). Depleted mantle model ages for the gneisses range from 1.7-2.3 Ga. The younger age may represent a mid-Proterozoic protolith age with incorporation of varying proportions of an older component, or a Pan-African component doing the same (Windley et al., 1996). 6. The Al-Baydah arc terrane, which contains green-schist grade rhyolites, andesites, basalts and tuffs which are folded, thrust-faulted and intruded by a variety of acid to basic rocks (Michel et al., 1989). Sm-Nd data for granitoids within the arc terrane yielded depleted mantle model ages ranging from 1.99-2.53 Ga; the undeformed appearance of the granitoids suggests late intrusion in the assembly of gneiss terrane, having been derived from ancient continental basement beneath the arc (Windley et al., 1996). The boundary between the Abas and Al-Baydah terranes is vertical high deformation zone with ophiolites along it and is interpreted as a suture (Windley et al., op. cit.). Along the eastern side of the Al- Baydah terrane the plutonics are in turn intruded by a major NW- trending andesite dyke swarms and a minor E-trending rhyolite dyke swarms. Making up between 75- 90% of the exposed unit over an area of at least 60 x 25 km, K/Ar apparent ages +-21 to 587 +-18 Ma, have been measured. And 40-39 Ar total fusion dates on hornblende of 693+- 12 and 585 +-11 Ma reported (Ba-Bttat et al., 1989; Windley et al., 1996). Other ophiolites close to the eastern margin of the terrane are imprecated and thrust-stacked with arc rocks. The terrane is interpreted as a juvenile Pan-African islands arc sutured to adjacent older gneissic terranes. The arc being thrust onto the gneisses during accretion as indicated by the northern end of the arc against the sandy-alluvial desert of the Sab’atayn basin which has an antiformal structure with granitic gneisses beneath (Windley et al., 1996). 67
  • 68. Fig. (2.5) Structural elements outline map with principal highs/uplifts and basins (Beydoun, As-Saruri and Baraba, 1996) 7. The Al-Mahfid terrane, consisting of belts of migmatised orthogneisses alternating with sheets of two groups of supracrustal rocks, indicating that the gneisses basement has been intercalated with two generations of cover rocks. The older of these cover rocks is up 2 km thick and consist of amphibolites, schists and thin quartzite beds whereas the younger is up to 1 km thick and consists of greenschist grade unmigmatised rhyolites and basaltic andesites, marbles and thin conglomerates. The gneisses give depleted mantle model age ranges 2.73-3.03 Ga and are interpreted as remnants of Late Archean continental crust; Pan- African reworking of the Archean complex added juvenile components, resulting in mixed model ages (Windley et al., 1996). 8. The Al-Mukalla terrane, undated but probably a Pan-African island arc by close geological affinity with the Al-Baydah arc terrane; this is made up of tuffs, porphyry lavas, volcanic breccias, rhyolites, basalts and dykes (the Tha’lab Group of Beydoun, 1964, 1966; Beydoun 68
  • 69. and Greenwood, 1968). These rocks are intruded by a major swarm of green schist grade mafic dykes (Windley et al., 1996). The only preserved outcropping occurrences in Yemen of metasedimentary Ghabar Group (of Infra-Cambrian to earliest Phanerozoic age) are found in fault-bounded depressions within the Al-Mukalla terrane (Beydoun, et al., 1998). To sum up, east of the Nabitah Suture five terrane have been identified in Yemen, three continental (Afif, Abas, Al-Mahfid) and two arc terrane (Al-Baydah and Al-Mukalla). The Yemen terranes indicate that east of the collage of arcs making up much of the exposed Arabian Shield in Saudi Arabia and continuing eastwards under the platform cover of thickening Phanerozoic sediments, several terranes of divers type and age such as those exposed in Yemen, probably underline the Phanerozoic. Windley et al. (1996) in consequence, present a simple but elegant tectonic scenario which can be summarised as follows: Following accretion of the arcs of the western Arabian Shield in Saudi Arabia and formation of the Nabitah Suture, the Afif terrane to the east of the suture and containing older gneiss basement, became the site of Andean type plutonic intrusions. The Abas gneiss terrane (Early-Middle Proterozoic), the Al-Baydah is island arc (Pan-African) and Al-Mahfid gneiss terrane (Late Archean-Middle Proterozoic) and the Al-Mukalla island arc (Pan-African) were all accreted during the Pan-African. Thus, this eastern boundary of the Arabian Shield marks a change from the accretion of island arcs in the west to accretion of Early Precambrian micro- continents and intervening island arcs. Further south in northern Somalia, two comparable but narrower terranes of juvenile volcanic arcs and intervening gneiss terranes occur, providing a link through Yemen between the island arcs of the northern or Saudi Arabian region and the southern gneissic East African Mozambique belt. 69
  • 70. 2.3 PHANEROZOIC Until the past two decades, the interpretation of the structural architecture and recognition of the Phanerozoic stratigraphic succession of Yemen were based almost entirely on surface geology. Miner conceptions consisted of some subsurface well data on unexposed sequences encountered in scattered borehole in the extreme NE of the country bordering the Rub al Khali desert and from the Tihamah area bordering the Red Sea. And from patchy geophysical surveys in these two areas and elsewhere (Beydoun et al., 1996; Beydoun, 1997). Much of the pre-Cenozoic stratigraphy is hidden under an extensive tableland consisting dominantly of carbonates in the eastern part and flood basalts and volcanics in the western part. With a large uplifted triangular-shaped block in between them, the Al-Mahfid uplift, consisting essentially of Precambrian rocks (often referred to as the Central Block). Pre-Cenozoic sequences are almost exclusively confined to the Jurassic and Cretaceous systems, almost exclusively resting directly on basement rocks, and are only to be seen in the faulted and dissected shoulders of the Gulf of Aden and Red Sea Rifts, on the High Plateau of western Yemen and around the edges of the Central Block. Paleozoic sequences do outcrop, but are essentially confined to the NW part of Yemen around the Sa’dah area and occur as a thin wedge between the basement and the Mesozoic succession. Only minor Infra-Cambrian to Early Cambrian metasediments are preserved above basement in small faulted depressions near Al Mukalla along the Gulf of Aden (Beydoun, 1964, 1966; Beydoun and Greenwood, 1968). Structurally, the eastern part of Yemen was seemingly dominated by the regional and broad E-W trending North Hadhramawt Arch; to its south lay the parallel trending Jiza ‘’trough’’-a broad faulted synclinal depression; further south nearer the coast, the parallel so- called South Hadhramawt Arch was located (Beydoun, 1964, 1966). (The South Hadhramawt Arch is now interpreted to be an artifact of Gulf of Aden Neogene rifting, representing the uplifted northern shoulder and the step-faulted of the Gulf of Aden Rift). A major NW-SE graben-like depression cuts obliquely across the western part to extend from Sa’dah region of the High Yemen all the way to Gulf of Aden near Balhaf; the floor of this depression is 70
  • 71. principally covered by superficial sediments and volcanics but exposes basement and Mesozoic rocks, especially along its SW shoulder, and abuts against the Tertiary tableland near its SE end. Fault and basement ‘’grain’’ patterns dissect the western part, with the ancient NW-SE Najd fault trend and its conjugate NE-SW trend being the most prominent, especially in the Central Block basement rocks, with subordinate N-S fractures being confined principally to the west of the 47th meridian; on these ancient trends are superimposed the more recent NNW-SSE and ENE-WSW and E-W Red Sea and Gulf of Aden trends associated with Late Tertiary extension and rifting. Extensive oil exploration drilling backed by variety of geophysical surveys, both regional (aeromagnetic and gravity) and more localised (reflection seismic), of reconnaissance and detailed nature from the late 1970s, began gradually to unravel a more complex Mesozoic tectonic history than was previously suspected. As indicated above, which had given rise to the formation of rift basins cutting across the country from west to east and generally trending NW- SE in the west but swinging progressively more easterly to WNW-ESE and W-E trends, eastwards. These basins are now known to have been initiated during the Late Jurassic by rejuvenation of the ancient (Late Proterozoic) NW-SE Najd fracture trend; the resulting rift basins accumulated greater thickness and subtly different facies of Jurassic sediments to those previously known from the outcrop sections. The timing of rift initiation and/or extension of structural activity ‘’youngs’’ eastwards and south-eastwards through Early Cretaceous in the centre, throughout the Cretaceous and into the Paleogene in the extreme east Beydoun, et al., 1996; Ellis, et al., 1996). The rift basins are separated by intervening uplifts; in the west, peneplaned Pre-Cambrian basement constitutes the surface, with all overlying Mesozoic (or Cenozoic) deposits either having been stripped off or else never having been deposited; locally, some Tertiary rocks rest directly on basement. The rifting episodes were related to stress regimes arising from progressive phases during the break-up of Gondwana commencing with the separation and drift of India (and Madagascar) and the opening of the Indian Ocean, then through the short-lived collisional- 71
  • 72. obductional event that affected Oman and the NE Arabian plate margin in the Late Cretaceous. The extensional events of the Late Paleogene resulted in the rifting and separation of Arabia from Africa in the Miocene and the opening of the Gulf of Aden and Red Sea; these in time gave rise to Neogene basins trending parallel to the two new rifts along ENE-WSW and NNW- SSE directions respectively (Beydoun, 1991). The Mesozoic rift basins exhibit, in general, considerably thicker and more rapidly varying stratigraphic sequences which reflect response to the successive episodes of rifting and subsidence, whereas the intervening highs were either exposed and undergoing erosion or received a veneer of shallow marine or fluviatile deposits. The type and provenance of basin fill gradually revealed by exploration drilling and seismic stratigraphy, has helped to unravel the overall paleogeographic changes stage by stage, although the exact relationships of these varied intra and inter-basin facies are only understood in a general manner (Beydoun et al., 1996). 2.3.1 EVOLUTION OF YEMEN ‘s PHANEROZOIC SEDIMENTARY BASINS Figure (2.5) shows the principal Phanerozoic sedimentary basins and inter-basinal uplifts in Yemen. These are presented in a generalised form in order to portray their main outlines and areal extents. Most basins, however, are broken up into a varying numbers of sub-basins and separating highs in consequence of response to initial and subsequent rifting phase and/or to horizontal movements along bordering master faults with resultant transpressional and transtensional adjustments along different sectors. A few of the depicted basins have not been confirmed either by detailed seismic and/or by deep drilling and their evolution remains speculative to varying degrees. These are discussed in more detail later. The present basin/uplift configuration has been generated from countrywide data available to the members of the Government-appointed Yemen Stratigraphic Commission and by drawing upon and modifying/amplifying earlier attempts at determining basin distribution. No claim, however, is made that Figure (2.5) portrays the definitive answer to pre-Cenozoic basin configuration although it is though that it indicates an accurate overall general picture (Beydoun, 1997; Beydoun et al., 1996). 72
  • 73. Prior to the start of the subsurface investigations, the structural framework consisted of the simple bi-axial Hadhramawt Arch and intervening Jiza’ trough in the east and the NW-SE rift cutting across the country in the west as outlined by Beydoun (1964, 1966). Subsequently, Isaev (1987) and Jungwirth and As-Saruri (1990), produced new structural framework maps for the country, respectively based on airborne magnetic survey results and on the extension of more localised but detailed geological survey results of the coastal area of Southern Yemen with the incorporation of earlier published more regional work. Paul (1990) utilised unpublished geophysical data obtained in former South Yemen up until the mid. 1980s and produced a schematic map of structural components. Beydoun (1988, 1991) and Beydoun et al., (1993) produced a simplified tectonic elements map covering all of Yemen which was based on some subsurface control, while Bott et al, (1992) similary produced a somewhat differing interpretation of the key basins and uplifts. Redfern and Jones (1995) also published their interpretation of Mesozoic basin distribution based on public domain, published and scouted data available to them up to the beginning of the 1990s. Similarly, Ellis et al., (1996) published a summary of structural basin inception and evolution results from a multiclient study carried out by Simon Petroleum Technology (SPT) for the Yemen Ministry of Oil and Mineral Resources in 1994, based on published, public domain and some selected new subsurface well and seismic data made available by some of the operating oil companies up until 1992/1993. These maps are detailed in those areas where the data set is good but they are subjective and speculative where they extend into areas where no subsurface data were made available and/or had not been acquired (Beydoun, et al., 1996). 2.3.1.1 PALEOZOIC BASINS The oldest Phanerozoic sedimentary basin of Yemen are the southern flank of Rub al Khali basin (principally located in Saudi Arabia but with the southern flank shared between Yemen and Oman) and possibly, the so-called San’a basin. The Rub al Khali basin constitutes a huge structural down warp originating as an intracratonic sag within the wide Gondwana shelf of the Early Paleozoic and becoming more differentiated as a subsiding platformal basin later 73
  • 74. during the Paleozoic and Mesozoic (Sykes and Abu Risheh, 1989; Beydoun, 1988, 1989b, 1991; Husseini, 1989; Dyer and Husseini, 1991). Much of the southern flank of the basin lies within northeastern Yemen, with the regional Paleozoic Hadhramawt Arch forming the southern basin margin onto which all Paleozoic and Early Mesozoic sedimentary sequences pinch out (Beydoun, 1989); northward into the basin, the flank slopes gently but in a step-like manner and the sedimentary column thickness increases from abut 2 km near the crest of the Hadhramawt Arch to over 4 km by the Yemeni-Saudi border. Geophysical surveys confirm the prolongation of the NW-SE Late Proterozoic/Infra-Cambrian Najd fault system of the Arabian Shield and its peripheries into Yemen, including the presence of Infra-Cambrian/ Early-Cambrian graben fill as discussed in some detail by Dyer and Husseini (1991) for the Saudi Arabia side. On some of the seismic lines, flower structures can be discerned at the shallower levels indicating that transpressional regimes operated during phases of horizontal movement on the Najd system (probably during rejuvenation phases in the Jurassic); these flower structures show decrease in relief with depth, suggesting disharmony with the basement or a detachment surface at Infra- Cambrian levels (Beydoun et al., 1996). The so-called San’a basin is located in NW Yemen mainly to the north of San’a and it was thought to reflect a Paleozoic depositional basin with Paleozoic deposits exposed on its northern and western sides; its exact outline and basinal axis orientation, however, are probably known. The Khaywan-1 exploration well drilled in the northern part, encountered less than 400m of Paleozoic sedimentary cover before terminating in basement; the Paleozoic is overlain by a thick succession of Jurassic carbonates and the basin may thus be of Jurassic age with Jurassic sediments outcropping around much of its presumed northern portion while thick Tertiary flood basalts and eruptives (Yemen Volcanic Group) hide its possible southern extension (Beydoun et al., 1996). The Socotra ‘’basin’’ lies to the south and SW of the Socotra archipelago and was thought to represent Mesozoic rift of Late Jurassic-Early Cretaceous age (Bott et al., 1994). Recent offshore drilling results, however, would seemingly suggest that the area might have 74
  • 75. evolved as a result of a late Karoo rifting episode (? Permian-Triassic) similar to some of the East African Karoo basins which have a Karoo-type sedimentary fill with marine influences. 2.3.1.2 MESOZOIC BASINS Tectonic stresses associated with Gondwana break up and separation of India/Madagascar from Afro-Arabia, rejuvenated movement along the old NW-SE Najd fracture system of Arabia during late Jurassic time. Initiating a series of rift basins across Yemen and breaking up the pre-rift early Upper Jurassic carbonate platform into alternating basins and intervening-uplifts. This activity seeming propagated from east to west and to south east in a sub-parallel manner with rift orientation angles gradually decreasing from NW-SE in the west (Ad Dali’ basin) to WNW-ESE in the east (Jiza-Qamar basin). In between these two extremes, the Sab’atayn-Balhaf basin occurs sub parallel to Ad Dali’ basin and is separated from it to the west by the Mahfid or Central Uplift and separated from Say’un-Masila basin to the east by the Jahi- Mukalla high; the Say’un-Masila basin, sub parallel in trend to both the Sab’atayn and Jiza-Qamar basins, is separated from the latter by Fartaq high (Fig. (2.5)). Episodic subsidence of these different basins was punctuated by sporadic but often only localised short pulses of inversion and erosion; these appear to have affected different sectors of most of these basins both in space and in time and have given rise to structural differentiation into sub basins, half grabens and intra-basinal horsts. This differentiation was probably principally related to intermittent horizontal motion along sectors of rift boundary master fault or along intra-basinal faults (Beydoun et al., 1996). Very little is known about Ad Dali’ basins east of Ta’iz or about its areal extent, since no seismic surveys or drilling activity have taken place there and all observations are entirely based on reconnaissance surface geology. It is thought that the Wadi Siham graben on the western side of the Yemen high plateau and cutting the shoulder of the Great Escarpment of the Red Sea Rift down to the Tihamah plain, forms the continuation to the NW of Ad Dali’ graben, the intervening area between the two being hidden under a blanket of Tertiary volcanics, it is also thought that rifting here is initiated slightly earlier, during the Jurassic (Callovian? -Oxfordian), 75
  • 76. than rifting of adjacent Sab’atayn basin to the east (Kimmeridgian and younger) (Beydoun et al., 1996). Sab’atayn basin rifting propagated south-eastwards from the Marib to the Shabwa and then the Hajar sectors; this basin is the only one of the Mesozoic rift basins of Yemen known to contain extensive deposits of terminal Jurassic evaporites throughout its sectors. The Balhaf graben on trend to the SE is separated from the Sab’atayn (evaporite) basin by the narrow Al Aswad high and was initiated in the Early Cretaceous with large thicknesses of coarse Cretaceous clastics being poured into the subsiding depression. As evidenced from the anomalous thicknesses encountered in wells Balhaf-1 and 2. The basin extends into northern Somalia (Beydoun et al., 1996). The Say’un-Masila basin as its name implies, is divisible into two sectors. The western or Say’un sector is more rift-like in its configuration and subsidence manner than the eastern or Masila sector, where deposits have intertongued more with open marine conditions; inception extends into the Early Cretaceous. The Jiza’-Qamar basin is much more sparsely drilled to Jurassic levels and thus less well constrained with regard to inception timing and areal distribution of the Jurassic system, especially as the few wells reaching basement are located structurally high blocks with only vestigial or no Jurassic preserved over them. Seismic sections tied to wells, however, suggest the presence of thicker and/or rapidly thickening Jurassic sequences off the drilled highs. The Jiza’ sector is characterised by thick Cretaceous deposits while the Qamar sector is characterised by both thick Cretaceous and Tertiary successions, with none of the few deep wells drilled to date penetrating to levels older than a very thick Upper Cretaceous sequence (Bott et al. 1992; (Beydoun et al., 1996). The so-called Sir basin located to the NW of the western extremity of the Jeza’ sector is though to have been formed in Late Jurassic-Early Cretaceous times and this was probably linked in a triple junction to the inception of the Sab’atayn and/ or the Say’un-Masila basin (Beydoun, 1991). Its approximate outline and the gross estimate of the thickness of its possible sedimentary succession are, however, entirely built on the interpretation of limited local gravity and regional aeromagnetic surveys and the apparent thick succession though to be present may 76
  • 77. be due to an artifact of different between lighter and denser basement rocks; this has to remain conjectural until confirmed or denied by adequate seismic and/or by the drill (Beydoun et al., 1996). 2.3.1.3 TERTIARY BASINS Tertiary basins are principally related to Neogene subsidence associated with Gulf of Aden and Red Sea extension and rifting and they are essentially located offshore. In the Gulf of Aden, the Mukalla-Sayhut and the Aden-Abyan basins run parallel to the Gulf of Aden ENE- WSW trend (Fig. (2.5)); marginal marine to brackish conditions prevailed during the Early Oligocene with rapid deepening to fully marine conditions from the Middle Oligocene. In the Red Sea, the onshore / offshore Tihamah basin extends parallel to the NNW-SSE Red Sea trend (Fig. (2.5)); here the major deepening episode did not begin until the late Oligocene, but the region was cut off from the Indian Ocean during the late Middle Miocene, giving rise to thick evaporite deposition (Hughes et al., 1991). 2.3.2 DEVELOPMENT OF PHANEROZOIC BASIN AND PLATFORM COVER 2.3.2.1 INFRA-CAMBRIAN/PALEOZOIC Paleozoic sedimentary cover overlying crystalline and metamorphic basement is known principally from the subsurface of the Rub al Khali basin. The subsurface of the northern part of the so-called San’a basin and/or the Marib-Al Jawf sector of the Sab’atayn basin and from outcrops in Sa’dah area and the peripheries of San’a basin in NW Yemen (Fig. (2.5)). Small isolated outcrops of folded and cleaved Infra-Cambrian clastics and carbonates known as Ghabar Group, and resting on Late Proterozoic volcanics, are preserved in Wadi Ghabar area some 50 km SW of Al-Mukalla and they are directly overlain by Mesozoic sediments (Beydoun and Greenwood, 1968). Similar but more volcaniclastic-dominated deposit is known from one of the Yemeni Rub al Khali wells in the Qinab area overlain by Paleozoic Cambro-Ordovician sandstones. Possible Infra-Cambrian metasediments unconformably underlie Jurassic rocks in 77
  • 78. the subsurface of the Al Furt-1 well drilled in the western part of the Jeza’-Qamar basin. (Figs. (2.5) and (2.6B)) In the Saudi sector of the Rub al Khali basin, Dyer and Husseni (1991) reported a distinct rift sequence below an identifiable/datable Middle Cambrian seismic reflector which they interpreted, using seismic stratigraphic principles, as being composed of three sequence: a lower indurated unit above basement (probably partly constituting the pre-rift sequence) is overlain by a marine-dominated unit with both carbonates and fine clastics and a top unit of discontinuous wedge-like proximal clastics or lacustrine sediments. They correlated these units with the Huqf Group of Oman but they state that unlike Oman, there is little evidence in the Rub al Khali sequences of any evaporites being present. On the Yemeni side of the Rub al Khali basin, only one penetration in the Qinab-1 well (Fig. (2.5)) encountered this Infra-Cambrian sequence, which consisted principally of a volcano-sedimentary succession (Fig. (2.6B)). That appears to represent the lowest unit of Dyer and Husseini (op. Cit.); the overlying carbonates and fine elastics and upper clastics or lacustrine sediments are apsent in this locality but are probably present deeper in the rifted basin a little further to the north. This succession has been named the Qinab Group. In the Al-Furt-1 well (Figs. (2.5) and (2.6B)) the deepest 1501m of the well penetration consisted of lightly metamorphosed shales and siltstones prior to the well being abandoned at total depth of 4,500 m. A regional seismic line running through the well exhibits a thick interval of parallel reflections below the total depth of the well, suggesting the presence of a thick succession of a sedimentary sequence overlying crystalline basement rocks. This hypothetical sequence would be the equivalent, at least in part, of the Huqf Group of Oman and the Ghabar Group of the Mukalla area and its presence on a drilled structural high would suggest that it may be quite widespread in the rest of the Jiza’-Qamar basin. The Huqf Group of Oman contains rich hydrocarbon source rock levels. The Paleozoic in the Sa’dah outcrop area and peripheries can be divided into two main units: 78
  • 79. An older undifferentiated clastic succession of moderate thickness, consisting predominantly of a lower quartz sandstone unit known as the Wajid Formation with a total age range that may span Cambrian-Carboniferous but contains many breaks in sedimentation. And an upper glaciogenic unit, the ‘Akbarah Formation of Late Carboniferous-Permian age. In the subsurface of the Yemeni sector of the Rub al Khali basin, a wedge-like succession of essentially coarse clastic Paleozoic sediments with many depositional breaks pinches out along the northern flank of the Hadhramawt Arch. Fig. (2.6A) Selected well correlation across different sedimentary basins and highs (Western Part); See Fig. (2.5) for location of wells 79
  • 80. Fig. (2.6B) Selected well correlation across different sedimentary basins and highs (Eastern Part) See Fig. (2.5) for location of wells These are onlapped southwards by Permian-Triassic and Jurassic sequence, which also pinch out before reaching the axial region (Fig. (2.6B)). The only successions to completely cover this paleo-high and extend beyond, are Cretaceous and Tertiary ones. No Paleozoic successions have been encountered in any of the relatively few boreholes drilled on the southern flank of the Hadhramawt Arch or in the Jeza’-Qamar basin, nor indeed anywhere else in the subsurface. (Other than that penetrated in the San’a ‘’basin’’ and in the western or Marib-Al Jawf part of the 80
  • 81. Sab’atayn basin and the possible Infra-Cambrian of the Al-Furt-1 well). This testifies to the antiquity of the Hadhramawt Arch (Beydoun, 1989) as an effective barrier against the advance of Paleozoic transgressions south of the feature. Paleozoic sediment has only been encountered in about four or five wells north of the Arch, the furthest occurrence southwards being in the Thamud-1 well (Figs. (2.5) and (2.6B)). On the basis of the sparse and discontinuous information relating to distribution of Paleozoic sediments in the Yemeni sector of the Rub al Khali basin, an attempt has been made to break the Paleozoic erathem down into formational units correlatable with their equivalent in southern Saudi Arabia. (Using the same nomenclature adopted there) Thus, a Cambro-Ordovician clastic succession encountered in some wells (including Qinab-1) above the Qinab Group is named and correlated with the Dibsiyah Formation of the Saudi Arabia sector of the Rub al Khali basin. A Silurian succession has been named and correlated with the Qalibah Formation of the Saudi Arabia sector and the Wajid area outcrop’s belt in Saudi Arabia and oxidised vestigial shale succession within this, with the organic-rich Qusaiba Member. A Devonian-Carboniferous clasic succession has been named and correlated with the Khusayyayn Formation and a Late Carboniferous-Permian sequence with the Juwayl Formation. All these units are grossly equivalent to the total Wajid Formation of the Najran outcrop area of SW Saudi Arabia and the Sa’dah outcrop area of Yemen to its south. In the Wajid outcrop belt north of Najran, detailed biostratigraphy and palynology have enabled the breakdown of the Wajid into the units discussed above which were given member status (Stump and van des Eem, 1994) but in the subsurface further east they have been given formational status. The subsurface Juwayl Formation of the Yemeni side appears to show evidence of glaciation and would thus be the equivalent of the Sa’dah area ‘Akbarah Formation outcrops; control is, however, sparse and for the present, they remain two different units of the same age. Palynomorphs have been the principal tool for the dating of most of the other Paleozoic units. 81
  • 82. 2.3.2.2 MESOZOIC Throughout the outcrop area and in the subsurface of most of Yemen there are no vestiges of any Triassic sediments. Except a wedge-like occurrence on the northern flank of Hadhramawt Arch/ southern flank of the Rub al Khali basin (Fig. (2.5)) and in the Karoo basin offshore southern Socotra. In all other areas, the Mesozoic is represented by the Lower-Middle Jurassic Kohlan Formation which consists of predominantly of sandstones and rests on peneplaned basement, other than in NW Yemen where it rests on the glaciogenic ‘Akbarah Formation (Carboniferous-Permian) where this is still preserved (see earlier). The Kohlan is overlain gradationally by neritic carbonates of the Shuqra Formation. In the paleo-uplift areas where the Jurassic is absent, Cretaceous sediments rest directly on basement (Fig. (2.5)) and also commence with basal clastics, which are followed by transgressive carbonates of the Qishn Formation. The paleogeographies of the Jurassic and Cretaceous periods however, differed in that during the Jurassic the Shuqra transgression and that of equivalent carbonates in neighbouring areas covered much of Yemen and extended westwards into Eritrea and southward into Somalia. The sea appears to have advanced from more than one direction, including from the SW and NW over western Yemen, and from the NE and east in the eastern part. During the Cretaceous however, the marine advance was from the east by a series of short transgressions followed by regressions, and marine conditions never covered western Yemen where terrestrial, fluvial and fluvio deltaic conditions prevailed. (Beydoun, 1964, 1966, 1970, 1997; Beydoun and Greenwood, 1968) The furthest marine carbonate deposition was limited to about the 470 meridian. Each transgression or high stand gave rise to carbonate depositional tongues advancing west and each regression or low stand permitted progradation of clastics eastwards. The intertonguing of the marine and fluvio-deltaic/terrestrial facies is principally located between the 490 30 and 510 meridians. The carbonate-dominated Cretaceous succession of the eastern part is the Mahra Group and its age equivalent clastic-dominated sequences to the west comprise the Tawilah Group. 82
  • 83. The ubiquitous Kohlan Formation at the base of the Jurassic system of Yemen, filled hollows in the undulating peneplaned topography, which essentially consisted of basement, rocks substrate. The Kohlan deposits were initially terrestrial-fluvial and subsequently littoral to transgressive shallow marine. The overlying Shuqra carbonates were initially widely distributed but are now, with all other younger Jurassic units, absent from a series of paleo-highs dissecting the country on NW-SE and easterly trends (Fig. (2.5)). It is not clear whether these Jurassic deposits were later eroded from such highs and / or were not deposited over them as a result of local uplift. Due to, differential movements accompanying the development of the rift basins from Kimmeridgian time to pre-Barremian time, or whether the areas with no Jurassic had remained elevated throughout the Jurassic period. This latter situation is certainly the case with the Hadhramawt Arch in the north which had remained a positive elevated feature for much of the Paleozoic and was rejuvenated in the Early Mesozoic, remaining an effective barrier until the Cretaceous (Fig. (2.5)). In the case of most of other highs or elevated blocks, however, it would seem that the removal or the non-deposition of Jurassic sediments was a contemporaneous phenomenon accompanying Late Jurassic-Early Cretaceous rifting. This view receive support from the observation that nowhere is there positive evidence of pinch-out or rapid thinning of sediments against an elevated paleo-high as in the case of the Hadhramawt Arch. Rather, it would seem that any variations in formational thicknesses are due to the effect of contemporaneous movements where the subsiding basins received thicker accumulations relative to the platformal but still submerged areas. If any of these latter areas were subsequently differentially elevated, they were partly or completely stripped of their sedimentary cover and never received further deposits so long as they remained uplifted. In late Shuqra time, the rejuvenation of tectonic movements in the region begins with the initial differentiation of the wide platformal shelf, ultimately leading to accentuated subsidence and rifting of the graben areas. The NW region of Yemen, however, remained platformal, where a relatively thick pile of carbonates were accumulated, ranging in age from Callovian to Early 83
  • 84. Tithonian; this succession is termed the undifferentiated Amran Group. In some sectors of the platform, however, such as the San’a region, some differentiation into other lithologies correlatable with formational units of the rift basins to the east, including the deposition of some evaporites, is possible. In the adjacent Sab’atayn rift basin (Fig. (2.5)), a thick succession of pelagic marls and claystones with turbidites and coarse clastics along the rift margins, was laid down in a rapidly subsiding basin and constitutes the Madbi Formation. Which is divisible into members and can be considered as the principal syn-rift formation spanning the Kimmeridgian to the early part of the Tithonian. It constitutes the principal source succession for Mesozoic hydrocarbons in Yemen. It is disconformably overlain by the evaporitic Sab’atayn Formation (Tithonian) which was periodically flooded by marine waters from the SE end and influxed by progradational deltaic sands at the NW end, which break up the formation into several members forming excellent hydrocarbon reservoir; these deposits represent the late syn-rift phase. Diachronously overlying is the semi-pelagic Nayfa (carbonate) Formation of Late Tithonian- Berriasian age, representing the final and post-rift Jurassic marine incursion into what had become a large embayment; regression and erosion followed this. The Sab’atayn basin is the only Jurassic rift basin in Yemen to contain evaporites (Beydoun, 1997). In the adjacent Say’un-Masila basin, (Fig. (2.5)), the Shuqra Formation is also succeeded by the Madbi as in the Sab’atayn basin but the Madbi of the Masila sector is of a more open marine pelagic carbonate facies rather than one of marls and claystones. It is a facies that continues upwards to embrace the overlying Nayfa Formation. In the Say’un sector, pelagic marls and claystones with occasional carbonates characterise the Madbi which, in the absence of the overlying evaporites of the Sab’atayn, is equivalent in its upper part to the lower portion of the evaporitic Sab’atayn. The overlying Nayfa here is equivalent in its lower part to the upper part of Tithonian evaporitic Sab’atayn and extends beyond that stage to the Berriasian with a gradual change upwards to a neritic depositional environment. Similar but more limited turbiditic deposits characterise some sectors of the Say’un-Masila basins rift margins. 84
  • 85. The Jurassic of the Jiza’-Qamar basin is little known and has only been penetrated in two wells located on structural highs in the western part. These indicate the presence of pre-rift Kohlan and Shuqra Formations; in the Al-Furt-1 Well (Figs. (2.5) and (2.6B)) a vestigial Madbi has been identified. Seismic sections tied to borehole control, however, suggest the presence of thicker or thickening and more complete Jurassic successions off the drilled structural highs. In view of the fact that the accelerated subsidence of this basin took place mainly during the Cretaceous, especially in the eastern sector, the Jurassic succession in the Qamar sector would be very deeply buried (at least 5,000 m or more). (Bott et al., 1992; Jungwirth and As-Saruri, 1990; Beydoun et al., 1993) The Balhaf basin, on trend with but separated from the SE end of the Sab’atayn basin (and its terminal Jurassic evaporites) by the Aswad high, was formed (as already indicated) principally during the Cretaceous (Figs. (2.5) and (2.6A)). It has the same pre-rift Kohlan and Shuqra units and a shelf-like Madbi Formation. Tectonic movements during Nayfa time resulted in a break between the Madbi and Nayfa successions (Bott in Beydoun et al., 1996), seemingly caused by a short phase of partial inversion and erosion as a consequence of transgressional stresses along one or more of the master faults. This occurred prior to relatively rapid subsidence and the deposition of pelagic porcellanites of the Nayfa, which were followed locally by shallower but apparently continuous deposition into the Valanginian before a regression followed by uplift and erosion set in (Beydoun et al., 1996). Carbonate deposition of the Nayfa Formation straddles the Jurassic-Cretaceous time boundary continuing into the Berriasian. In the eastern part east of the Mukalla high, deposition continued into Late Valanginian time, where shales, carbonates and clastics of the Sa’ar Formation follow the Nayfa without any apparent break in the Wadi Masila gorge. (This situation is also present on a very local scale west of the Mukalla high at the eastern side of the Balhaf basin in the lower Wadi Hajar area, see above.) The Sa’ar exhibits a marked shoaling of facies with shales and prograding carbonates terminating with further shoaling and sand deposition prior to Late Valanginian uplift and 85
  • 86. widespread erosion. The Sa’ar Formation was previously unrecognised either in outcrop or in the subsurface. During drilling the Say’un sector of the Say’un-Masila basin from 1992, a new unit lying between well known Qishn Formation sequences above and an equally well- established Nayfa Formation sequence below was differentiated. This recognition was followed by detailed field studies in the Wadi Masila gorge where the new unit was soon identified in surface exposures and its relationship to the overlying and underlying units established. It is not recognised in outcrop in the Ras Sharwayn area and is only locally preserved in two localities in the lower Wadi Hajar area west of Mukalla, as stated above. The Sa’ar Formation is unconformably overlain by the Hauterivian-Barremian Qishn Formation which constitutes the basal unit of the carbonate-dominated Mahra Group of the eastern part of its coeval and intertonguing clastic-dominated Tawilah Group of the western part. The Qishn can rest on Sa’ar, Nayfa or directly on peneplaned basement over the Jahi-Mukalla and other paleo-highs and clearly represents the first widespread transgressive unit of the Cretaceous following Late Valanginian erosion and quasi-peneplanation. It commences with thin transgressive sands but intertongue with clastic westwards; these are indicators of short transgressive pulses in that direction. West of about 470 meridian, the carbonates pinch out and the Tawilah Group is no longer divisible into formations, consisting entirely of fluvio-deltaic and continental clastics (Beydoun, 1997). The Qishn Formation is disconformably overlain by the Albian-Cenomanian carbonate- dominated Fartaq Formation, marking a new transgression from the east. The succession commences with basal transgressive sands, which become dominant westwards to mark up the roughly coeval and partly intertonguing Harshiyat Formation. West of about the 500 meridian, the Fartaq (by now divisible into members recognisable eastwards) is only sporadically recognised in the form of carbonate tongues in a sandstone-dominated Harshiyat Formation. By about 470 30’, the last of these, the Sufla Member separating the clastic Harshiyat from the overlying but equally clastic-dominated Mukalla Formation, has pinched out and the Tawilah Group to the west becomes again undifferentiated. 86
  • 87. In the Jeza’-Qamar basin, the Qishn may overlie the Sa’ar of the Jeza’ sector of the basin without a noticeable break. As demonstrated by the sequences encountered in the Al-Furt-1 well where a thick succession of shales, marls and argillaceous limestones constituting Sa’af Member of the Qishn, overlies Sa’ar shales and suggests accelerated subsidence in that basin during Hauterivian-Barremian time without evident indication of a Late Valanginian erosion (Figs. (2.6B)). The subsidence continued in this western sector throughout Qishn and Fartaq/Harshiyat times. Another regression occurred in Late Cenomanian time with accompanying erosion, to be followed by a gradual slow inundation from the east depositing the shallow marine clastics of the Mukalla Formation and the carbonate tongue of its Lusb Member. This marine clastic unit intertongued with progradational deltaic clastics and fluvial sediments coming in from the west. In Early Campanian time a limited marine ingression restricted to the Jeza’-Qamar basin came in from the east. This is represented by the Dabut Formation, consisting of marine carbonates and clastics limited to the area east of the 510 30’ meridian and intertonguing with fluvio-deltaic deposits of upper Mukalla Formation which dominates to the west. Another regression occurred during the Early Maastrichtian, to be immediately followed by another transgressive advance of the sea in the late Maastrichtian which laid down the Sharwayn Formation over most of eastern Yemen; the carbonates of the Sharwayn reached the 490 meridian, intertonguing into the clastics of the upper Mukalla. This formation had become entirely continental westwards and was undergoing erosion. This last transgressive pules of the Cretaceous ended in regression and erosion (Beydoun, 1997). 2.3.2.3 CENOZOIC The Cenozoic or Tertiary erathem commenced with a powerful Late Paleocene to Early Eocene transgression represented by Umm er Radhuma Formation. This disconformably overlies the Sharwayn/Mukalla Formations; it consists principally of neritic blanket-like carbonates with an intermittent thin basal shale member and extends in outcrop as far west as the 470 meridian. A shallow marine-littoral sandstone succession in the San’a region (about the 87
  • 88. 440 meridian), the Majzir Formation, with Paleocene/Eocene fossils, most probably represents the westernmost extent or shoreline of the Umm er Radhuma and the overlying Jeza’ Formations (Beydoun and Sikander, 1992). It is difficult, however, in view of lake of outcrops in the intervening area, to follow this in the field. The Tertiary tableland consists of a blanket of sediments covering Yemen east of the 470 meridian, known as the Hadhramawt Group. Its basal unit is the Umm er Radhuma which is overlain by the Lower Eocene Jiza’ Formation consisting of alternations of shallow water carbonates and shales which outcrop westwards as far as the 470 meridian. To the east, however, from approximately the 510 30’ meridian eastwards, it is no longer separable from the underlying Umm er Radhuma and the age of the latter unit embraces Early Eocene. The Jiza’ is in turn overlain by the restricted environment but arealy extensive anhydrites of the Rus Formation which terminate westwards at the 470 meridian but extend eastwards into Oman. The sea once again transgressed from the east to deposit the marine Habshiyah Formation, closely similar to the Jeza’ Formation in facies, and its transitional littoral/shallow neritic correlative, the Kaninah Formation in the west. The terrestrial but correlative Mayfa’ah Formation occupies the area between the Kaninah westwards to approximately the 470 meridian (As-Saruri and Langbein, 1995). The 470 meridian line seemingly represented a hinge line between eroding terrestrial environments to its west and shoreline of marine depositional environments over part of the Cretaceous (Qishn carbonates limit) and throughout the Paleocene-Middle Eocene. No Upper Eocene deposits are known in Yemen. This was a time of regional uplift which was represented in western Yemen since the Early Eocene by intermittent volcanicity, culminating in Oligocene-Miocene times with extensive extrusive and plateau flood basal outpouring and volcanic activity which make up the Yemen volcanic Group (the Yemen ‘’Trap Series’’). The volcanicity is related to extension and rifting which culminated in Neogene opening of the Gulf of Aden and Red Sea Rifts (the Yemen ‘’Volcanic Series’’). 88
  • 89. Again, to the east of the 470 meridian, marine incursions into coastal embayments on both sides of the newly foundering Gulf of Aden gave rise to the heterogeneous deposits of the Shihr Group of Oligocene-Pliocene age. Offshore, in the subsiding sector of the rift, thick clastics were being poured in, which were essentially of turbiditic nature. Onshore, the Shihr Group deposits reflect disconnected basin deposition, and facies are provenance and environment-dependent, whereas offshore more uniform clastic deposition prevails with occasional shoal carbonates (As-Saruri and Lagbein, 1996). Initially, marginal marine to restricted evaporitic deposition characterised the Lower Oligocene deposits, to be followed in the Middle Oligocene by major deepening and rapid syn-rift marine clastics deposition (Hughes et al., 1991). In the Red Sea, the initial rifting was a Late Oligocene age and was followed by deposition of a thick pile of syn-rift sediments of the Tihamah onshore/offshore basin, culminating in Middle-Upper Miocene evaporite deposition on a wide scale. These were succeeded by post-rift Pliocene clastics and carbonates while onshore and along the Red Sea axial fissure, extrusive activity continued into modern times (Beydoun and Sikander, 1992). These succession are now collectively called the Tihamah Group but the base has not been reached in any of the deep wells drilled in the area to date. 89
  • 90. CHAPTER 3: GEOLOGY OF YEMEN 61 3.1 INTRODUCTION 62 3.2 ARCHEAN-PROTEROZOIC BASEMENT 63 3.3 PHANEROZOIC SEDIMENTARY ROCKS 69 3.4 STRUCTURE AND TECTONICS OF YEMEN 95 3.5 SURFACE UPLIFT AND DENUDATION 100 3.5.1 SEDIMENTOLOGICAL EVIDENCE FOR THE UPLIFT HISTORY 100 3.5.2 FISSION TRACK ANALYSIS OF THE EXHUMATION HISTORY 101 3.5.3 GEOMORPHOLOGICAL EVIDENCE FOR UPLIFT AND DENODATION HISTORY 101 3.6 GEOLOGICAL HISTORY 105 90
  • 91. CHAPTER 3 GEOLOGY OF YEMEN 3.1 INTRODUCTION Due to Menzies, et al., 1994 (See McCombe, 1994) the geology of the Republic of Yemen is very diverse and includes metamorphic rocks, that formed in the first few billion years of earth’s history, transected by a failed Jurassic rift system related to the break-up of the supercontinent of Gondwana land, and a Tertiary to Recent geological history determined by propagating Indian Ocean Ridge which triggered the opening of the Gulf of Aden-Red Sea rift. Within the Precambrian basement of the Republic of Yemen, several possible Archean nuclei exist sutured together by Proterozoic oceanic terranes. After late Precambrian orogenies ceased, erosion of the basement continued and resulted in a peneplained surface upon which a thin (less than a 1.000 m) cover of Palaeozoic sandstone and shales, some possibly of glacial origin was deposited. Rifting associated with the break-up of Gondwana land affected Yemen with the formation of the Ramlat As Sab’atayn Graben that is sited along major crustal shear zones between Arabia, Africa and India. Minor fluctuations in sea level occurred during the Jurassic, affecting deposition of a relatively thin clastic (Kohlan) and carbonate (Amran) succession. A major regression towards the end of the Tithonian resulted in deposition of salt and gypsum in western Yemen. Uplift and erosion of the pre-Cretaceous rocks was followed by deposition of shallow-marine to continental siliciclastics and minor carbonate lenses towards the east, the Tawilah Formation. In a marginal marine subsiding basin centred in the southern Arabian Plate during Cretaceous time. The last 30 million years of Yemen’s geological history have shaped the landscape presented today. North- eastward movement (1.5-2.0 cm/yr.) of the Arabian plate from African plate and formation of the Gulf of Aden were, in part, coincident with a massive thermal change caused by upwelling of the Afar mantle plume. Sedimentation all but ceased in western Yemen when some three to 4.000 m of volcanic material was erupted from central volcanoes. In eastern Yemen shallow marine sedimentation continued into the Eocene depositing several hundred metres of limestones and evaporites. Lithospheric loading, thermal changes, and emplacement of buoyant granites all contributed to Oligo-Miocene uplift of the Red Sea margin. Subsequent exhumation led to removal of pre-Miocene rocks and deposition of up to 4.000 m of Miocene to Recent clastic sediments in the Tihama Plain bordering the Red Sea. In eastern Yemen, Miocene to Recent sedimentation occurred in coastal embayments (less than 3.000 m) along 91
  • 92. a coastline very similar in shape to the coast today. A Neogene syn rift succession of clastics and carbonates is preserved along the coast uplifted in the footwall of the Gulf of Aden rift. 3.2 ARCHEAN-PROTEROZOIC BASEMENT Precambrian rocks are found throughout western Yemen from the north-west around Sa’dah and as far east as Ras Sharwayn (Fig. (3.1); Table (3.1) and Fig (3.2)). Traditionally the basement rocks in Yemen are though of as part of the Proterozoic Arabian-Nubian shield which covers norteast Africa and the Arabian Peninsula (El-Anbaawy, 1984; Stoeser and Camp, 1985; Ba-Bttat et al., 1989; Ba-Bttat, 1991; Whitehouse et al., 1993). Fig. (3.1) Geographic map of Yemen 92
  • 93. Table. (3.1) Summary of geological mapping in the Republic of Yemen. 93
  • 94. Fig. (3.2) Index to geological mapping in Yemen The basement rocks of north-west Yemen have not been dated but appear to be of Proterozoic age and comprise metavolcanic and metasedimentary belts produced in arc environments intruded by post-tectonic granites and granodiorites (Figure (3.3)). In north-west Yemen, the basement rocks have a north-south to northeast-southwest structural trend and a petrogenetic affinity to the accreted arc terranes that constitute the Nabitah orogenic belt of Saudi Arabia (Figure (3.3)). Stoeser and Camp (1985) divided the Arabian Shield into five terranes and it is known that two of these terranes, the Asir and Afif, are found in northwestern Yemen (Figure (3.3)). Volcanic arc, ocean plateaus and basins comprise the Asir terrane (730 to 760 Ma) and the Afif terrane consists of magmatic arcs formed on continental and oceanic crust. Although the Nabitah suture contains ultramafic bodies and serpentinites in Saudi Arabia, in Yemen these rocks are far from easily recognisable as ophiolites (Figure (3.3)). 94
  • 95. Fig. (3.3) Precambrian basement geology of Yemen, (Menzies, et al., 1994); after A – Northwest Yemen (Geomin 1985); B – Northeast Yemen (Christmann et al., 1984); C – Sana’a – Al-Bayda (Kruck et al., 1991); D: Yaffa (Strojexport. 1988); E – Lawder – Wafid – Beyhan (Lobunets et al., 1988); and F – Habban-Al-Mukalla (Scharamm et al., 1986). While the basement rocks of northwestern Yemen (Figure (3.4)) bear a remarkable similarity to the basement rocks of Saudi Arabia, basement rocks in southern to southwestern Yemen are more akin to the basement rocks of Somalia (Lobunets et al., 1988; Veselov, 1990). Strojexport (1988) sub-divided the basement rocks of eastern Yemen into several groups including the Yaffa Group of monotonous grey gneisses; interlayered dark and light gneisses with interlayered granites and basic gneisses; metavolcanics and metasediments. Lobunets et al. (1988) described the Mahfid Block as possibly being early Proterozoic in age and therefore related to the Arabian-Mozambique basement. In southeastern and southern Yemen it was proposed by several groups (Schramm et al., 1986; Strojexport 1988; Lobunets, 1988; Veselov, 1990) that rocks (e.g. grey gneisses) significantly older than the Proterozoic basement rocks of northwestern Yemen might exist between Rada and Al Baydah (Fig. (3.1)). While Strojexport (1988) reports ages of 455-1112 Ma for representative basement rocks they point to the presence of an ‘’older element’’ in the Yaffa Group. Moreover Labunets et al. (1988) believe that part of the basement is early Proterozoic in age. 95
  • 96. Recent chronological and isotope work (Whitehouse et al., 1993) on basement samples (Ba-Bttat, 1991) indicates that a large Precambrian terrane, which extends east from Rada to Al Baydah and the Gulf of Aden (Fig. (3.1)). Contains Archean elements. The gneiss blocks contain grey gneisses with enclosed amphibolite dykes and granite sheets and the gneisses have late-Archean Sm-Nd model ages of 2700-2900 Ma. (Stoeser et al., 1991; Whitehouse et al., 1993). According to Whitehouse et al. (1993) the cratonic nuclei are sutured together by northeast- trending island arc terranes (Figs. (3.3) and (3.5)). While the Al Mukalla Proterozoic terrane (Fig. (3.3)) contains components that are possible Upper Proterozoic to Phanerozoic in age, the area around Al Baydah contains areas of Archean age separated by lower Proterozoic mobile belt. In contrast to Archean gneisses terranes and the basement in the north-west, the Proterozoic mobile belt around Al Mukalla contains more sedimentary and volcanic units and basalt-rhyolite flows and volcaniclastic deposits are also found within this unit (Schramm et al., 1986). The amount of granitic to granodioritic intrusives is much less than in the north-west. Overall a fundamental petrogenetic change occurs from the northwest to the southeast in that the Northwest tends to be more oceanic (Proterozoic) while the southwesteast is more cratonic (Archean-Proterozoic) (Figs. (3.3) and (3.5)).The late Proterozoic Murdama Formation of Saudi Arabia, that consists of clastics, limestones and local Volcanic rocks is believed to be a late tectonic melange (Robertson Group, 1992) which had a continental affinity in the west and possibly a marine affinity in the east. It is believed to have been deposited as a result of erosion of the Nabitah Orogen at the end of the Proterozoic. Uplift at the end of the Proterozoic led to erosional denudation producing a peneplain. Fig. (3.4) Correlation of Precambrian units in northern Yemen (Menzies, et al., 1994; after GEOMIN, 1985 and Chrismann et al., 1984) 96
  • 97. Fig. (3.5) Geology of Yemen modified (Menzies, et al., 1994; after Robertson Group (1992) 3.3 PHANEROZOIC SEDIMENTARY ROCKS Cambro-Ordovician / Permo-Carboniferous: Wajid Sandstone The Wajid Sandstone (Figure (3.6)) occurs in southern Saudi Arabia and Northern Yemen (Geukens, 1966; Powers et al., 1966; Beyth, 1973; Christmann et al., 1984). This formation comprises thick continental sandstones and coarse siltstones with well developed cross-bedding (Robertson Group, 1992) but limited development of lensoid, intraformational conglomeratic gravels. While the sandstone reach a maximum thickness of 1.000 m overlying basement north of San’a (Figure 5) they are generally 200 m thick. Greenwood (1980 a;b) described the basal contact with basement rocks as an angular unconformity (cf Dabbagh and Rogers, 1983) and the upper contact, with overlying shales, as an unconformity (Figure (3.6)). Roland (1979) first suggested that the Wajid sandstone was Carboniferous-Permian in age and Dabbagh and Rogers (1983) believe it to be Cambro-Ordovician on the basis of fossil data (see also Geukens 1966; Beydoun 1988) (Figure (3.6)). The area of outcrop of the Wajid Sandstone is restricted to northwestern Yemen and it wedges out to the south (Fig. (3.5)). This has important implications about the location of possible basement highs or palaeoslopes at this time and is presently under investigation using fission track techniques (Yelland, Menzies and Hurford, 1994 unpublished data). 97
  • 98. The depositional environments ascribed to the Wajid sandstones vary from aeolian to glacial and shallow marine epicontinental to deltaic (Robertson Group, 1992). Michel (1989) interpreted the Wajid sandstones as fluviodeltaic facies but glacial deposits have also been described within the Wajid sandstones (Helal, 1965). Dabbagh and Rogers (1983) divided the Wajid into northern marine unit in Saudi Arabia and a southern fluviatile unit in Yemen. Christmann et al., (1984) described a lower fluvio-deltaic succession and upper deltaic to shallow marine unit. Most investigators agree that sediment transport was from the south and southeast to the north and northwest (Geukens 1966; Greenwood 1980a,b; Dabbagh and Rogers, 1983). Permian: Akbra Shale The Akbra Shale is absent in the western part of Yemen near the Tihama Plain and tends to be restricted to the Yemen Highlands (Fig. (3.5)). The main lithologies are laminated mudstones, siltstones and shales (Roland, 1979; Kruck et al., 1984; Christmann et al., 1984), in places containing large, up to one meter diameter, isolated granitic boulders suspended in fine-grained matrix (Fig. (3.7)). Weakly-striated, bullet-shaped dropstones and polished bedding surfaces have also been observed. The Akbra Shale reaches a maximum thickness of 130 m, with an average thickness between 40 and 80 m (Figs. (3.6) and (3.7)). 98
  • 99. Fig. (3.6) Stratigraphy of Yemen (By Menzies, et al., 1994;after Beydoun, 1964) 70 99
  • 100. Fig. (3.7) Stratigraphy column of the Akbra Shale, Yemen (Davison et al., 1994) It rests unconformably on the Wajid sandstones (Roland, 1979) or overlaps and rests directly on Precambrian basement. The upper contact is always an angular unconformity with the Kohlan Formation or the Amran Group (Figs. (3.6) and (3.7)). Palynological data has been used to date equivalent strata in Saudi Arabia as Permian (Kruck and Thiele, 1983). The depositional environment of the Akbra Shale is thought to be lacustrine or fluvio-glacial. Apart from dropstones and rounded striated basement rocks in this unit, tillite horizons have been reported and the underlying basement rocks are polished and show glacial striations (Fig. (3.7)). This observations indicate that ice movement may have been from the northeast to southwest. Regionally the Akbra Shale is correlated with other glacial deposits in Ethiopia, Saudi Arabia and Oman (Beyth, 1973; McClure, 1980). Other Palaeozoic Strata Seismic data point to the existence of Cambrian age strata in the northernmost parts of the Hadramaut and Mahra provinces (Robertson Group, 1992). While Silurian, Devonian, Carboniferous and Permian strata are believed to exist in some borehole sections (World Bank, 1983) Jurassic sediments directly overlie Precambrian basement 100
  • 101. (Figs. (3.5) and (3.6)) in many other regions (Mills, 1992). Siebens (1977) reported Permo-Carboniferous limestones and sandstones that unconformably overlie basement rocks from the southeastern part of the island of Suqatra. The Siebens offshore well encountered more than 1,000 m of Permo-Triassic rocks, directly overlying basement. L-M Jurassic: Kohlan Sandstone Beydoun and greenwood (1968) reported that the Kohlan Sandstone (Fig. (3.6)) occurred throughout Yemen as a minor lithological unit. The Kohlan Sandstone averages 60 m in thickness and appears to fill irregularities in the underlying eroded surface (Beydoun, 1982). Recent studies at Wadi Laah in eastern Yemen (Nichols, 1993 unpublished data) (Fig. (3.1)) show that a 50 m thick basal unit of dark purple and gray shales and siltstones lies directly on granitic rocks of the Precambrian basement. This in turn is overlain conformably by very coarse, arkosic sandstones and siltstones. The sandstones are extensively cross-bedded and occur in channel-fill units (Fig. (3.8)); the siltstones are mainly purple in colour and the pattern of mottling indicates pedogenetic alteration. Dessication cracks have been observed in muddy-siltstones. Towards the top the sandstones become paler and purer quartz arenites. They show evidence of bi-polar cross-bedding, possibly indicating a tidal influence close to the main contact with the limestones of the overlying Amran Group. Lobunets et al. (1988) report basement overlain by quartz pebbles in an arkosic matrix, sandstones containing plant fragments, siltstones containing silicified tree trunks and plant remains, and quartzose to calcareous sandstones. The basal contact is always an unconformity resting on Precambrian basement, Wajid Sandstone, Akbra Shales (Fig. (3.6)) or, according to some reports, pre-Jurassic volcanic rocks in eastern Yemen (Schramm et al., 1988; Lobunets et al., 1988). Lobunets et al. (1988) reported that while in many places the underlying basement rocks are fresh and compact, other contacts are characterised by the presence of a weathered crust. Kruck and Thiele (1983) reported that a gradational contact existed between the Kohlan sandstone and the overlying basal limestone of the Amran Group. This contact is apparent as transitional lithologies or an abrupt, but conformable, change in lithology. Beydoun (1982) considered the Kohlan Formation to be Middle Jurassic in age (Fig. (3.6)). A Middle Jurassic age has also been suggested for the Kohlan Formation in the Masila Area much farther to the east (Mills, 1992). While Strojexport (1988) reported no macrofossils in the Kohlan in southeastern Yemen, Lobunets et al. (1988) reported the presence of the fern Piazopteris branneri which is of Middle to Upper Jurassic age. In addition, the presence of pelecypods and the algae Marinella lugeoni, point to a Jurassic age (Lobunets et al., 1988). From studies in western 101
  • 102. Yemen (Davison et al., 1994), it is apparent that the Kohlan Formation is a transgressive unit consisting of a lower continental clastic sequence which passes upwards into shallow marine clastics, and finally into the marine limestones of the Amran Group. A fluvio-glacial origin has been suggested for the Kohlan Formation in northwestern Yemen where it has been described as the Affar Formation by Kruck and Thiele (1983) and El Nakhal (1987). As noted by the Robertson Group (1992) the facies variations reported within the Kohlan are consistent either with transgression from the east, or a west to east palaeoslope. Fig. (3.8) Stratigraphy column of the Kohlan Sandstone, Yemen (Davison et al., 1994) 102
  • 103. Jurassic Amran Group The stratigraphy and the geological evolution of the Mid to Late Jurassic rocks of Yemen is complex and intimately linked to the development of extensive, hydrocarbon bearing, northwest-southeast and east-west graben systems (Fig. (3.9)). Therefore graben and intergraben, or platform, regions have different stratigraphies (Fig. (3.10)). This situation is further complicated by the fact that the grabens are only known from the subsurface and have a stratigraphic nomenclature which differs from that established from the very different, and still relatively poorly understood, outcropping regions of the platform. The most recently published information on the Jurassic and, possibly, early Cretaceous (Kruck et al., 1991) stratigraphy is summarised in Fig. (3.10) for four areas on a more or less east west travers across Yemen including the outcropping Western platform area north of Sana’a (Al Thour, 1992), the outcropping graben shoulder areas northwest of Dhamar to Marib (Kruck et al., 1991), the subsurface Ramlat As Sabatayn Graben (Schlumberger, 1992), to the Eastern Platform of the Hadramaut-Mukalla region (Beydoun and Greenwood, 1968; Haitham and Nani, 1990). While the correlations are based on the quoted ages of the stratigraphic units in these references, many stratigraphic thicknesses are still unknown or unpublished. A summary stratigraphic logs of the Amran limestone from the Al’Ayen area of Yemen (longitude 15o 35’E; latitude 43o 50’N) is given in Fig. (3.11) (Al Thour, 1992). Western platform. The region north of Sana’a contains the largest outcrops of the Amran Limestone but is still poorly understood (Figs (3.9) and (3.10)). El-Anbaawy (1985) divided the Amran Group into seven teen facies and Christmann et al. (1984) divided it into ten units. None of these earlier conclusions have been accepted by more recent research (Al Thour, 1992; Kruck et al., 1992). Al Thour, (1992) divided the Amran Group of this area into three formations (Figs. (3.10) and (3.11)). The thickness measured, but incomplete sections, are 520 m thick with a composite total thickness of about 900 m (Figs. (3.10) and (3.11)).A biostratigraphic zonation based on forminifera (Fig. (3.11)) has been established by M. Simmons (in Al Thour, 1992). The lowest Al khothally Formation (Fig. (3.10)) comprises transgressive bioclastic limestones over the siliciclastic marine sand of the Kohlan (Fig. (3.6)) which pass upward into regressive shoaling-up, high energy peloidal and bioclastic grainstones and packstones. The overlying Raydah has similar, shallowing-upwards cycles which are locally rich in corals and stromatoporoids or ooids. Tops of cycles are marked by hardgrounds. These shoal areas interfinger with intraplatform basins which accumulated muddier facies. The uppermost Wadi Al-Ahjur 103
  • 104. Formation (cf El-Anbaawy, 1985) is regressive and shallows up through algal (Permocalculus) rich limestones to quartz rich limestones which are cut by a karstic surface developed on top of Amran. North of Sana’a (Fig. (3.1)), the Amran carbonates were uplifted and eroded to produce a minimum relief of some 50 m prior to deposition of the onlapping shallow-marine sandstones at the base of the Tawilah Group (Fig. (3.6)). Elsewhere the boundary is either conformable, with intervening dark grey-black and brown shales, or disconformable, with a solution-modified, palaeokarstic upper surface (Bosence, 1994 unpublished data). These late Jurassic shallow-marine carbonate facies extend to the western-most exposures of the Amran on the tilt-blocks of the Tihama Plain (Bosence, personal observation) (Fig. (3.1)). There is therefore no evidence for the Red Sea being sited over an earlier Jurassic graben (Menzies et al., 1992). Fig. (3.9) Major Jurassic palaeographic and tectonic features of Yemen 104
  • 105. Fig. (3.10) Nomenclature pertinent to Jurassic stratigraphy across Yemen from the Bayda area (Al-Thour, 1992), the graben shoulder northwest of Dhamar-Marib (Kruck et al., 1991), the Ramlat As Sabatayn graben (Schlumberger, 1992) and the eastern platform (Beydoun and Greenwood, 1968; Haitham and Nani, 1990). 105
  • 106. Fig. (3.11) Stratigraphy of the Amran Limestone from Al-Ayen area, Yemen (By Menzies, et al., 1994; after Al-Thour, 1993) Graben shoulder. Outcrops to the west of Sana’a were mapped by Kruck et al. (1991) and appear to show a different history to that of those north of Sana’a even though they have not been studied in such detail (Figs. (3.9) and (3.10)). A phase of pre Callovian uplift is evident from the presence of a lower, highly reflective, shelf facies, which is likely equivalent to the Shuqra Formation of the earlier workers, resting directly on the Precambrian basement. The beds comprise alternating thickly bedded shallow marine carbonates and thinly bedded fossiliferous marls and limestones. Overlying and laterally interfigering this units is the Lower Basin facies (Fig. (3.10)) which contains fine grained brownish bioclastic, locally rich in corals and oysters, limestones and dolomites. The Upper Basin facies (Fig. 106
  • 107. (3.10)) comprise marls, bituminous shales and gypsiferous shales and sandstones locally occurring in salt domes in the Ramlat As Sabatayn area. These two basin facies are likely to be equivalent to the Sabatain Formation of El- Anbaawy (1984). In this region there is a transitional unit with early Cretaceous shallow marine and fluviodeltaic clastics marking the conformable junction with the Tawilah Sandstones (Fig. (3.6)). Ramlat As Sabatayn Graben. This hydrocarbon rich Jurassic-Cretaceous graben (Fig. (3.9)) contains very much thicker sequence with source rocks in deep-water organic rich shales and evaporite related mud rocks and reservoirs in interbeded sandstones and dolomitised limestones, with evaporite seals (Schlumberger, 1992). Only the Oxfordian and early Kimmeridgian strata are referred to the Amran Group in the Ramlat As Sabatayn Graben (Fig. (3.10)). The Saba Formation rests unconformably on the Kohlan and is a shallow marine high energy limestone, now dolomitised and with a vuggy porosity (Schlumberger, 1992). This would appear to be a similar unit to the Shuqra, or Shelf facies and Al Khothally and Raydah Formations of the surrounding platform areas. The overlying Arwa Formation (Fig. (3.10)) shows the first evidence of tectonic activity in that muddier (deeper?) limestones, shales and sandstones occur in association with basement cutting extensional faults. This is followed by active rifting and drowning of the Arwa carbonates by deep basinal non-carbonate shales of the Meem Formation (Fig. (3.10)), and distal turbidites and hemipelagic claystones and limestones of the Lam Formation, the major source rocks of the basin (Schlumberger, 1992). These interfinger into marginal scarp-related submarine fans introducing conglomerates and sands of the Henneye and Ayban Formations (Fig. (3.10)) into the basin. These deep basinal facies appear to correlate with the Basin facies of the Sabatain Formation outcropping in the Marib area and with the Tithonian regressive Wadi Al-Ahjur Formation of the platform. A major regression took place in the area at the end of the Tithonian. A karstic surface is found in the western platform and the Ramlat As Sabatayn Graben basin becomes isolated and restricted, with the formation of cyclically arranged evaporites, sandstones and organic rich shales of the Amla’ah. These area overlain by the Tawilah Group clastic of the Naifa and Tawilah sandstones (Fig. (3.6)). Eastern platform. The region to the east of the Balhaf Graben and to the west of the Mukalla High (Fig. (3.9), Beydoun, 1964)) has a stratigraphy more in common with the western Platform of Yemen than the intervening Ramlat As Sabatayn Graben. This applies both to the thickness (733 m) and to the largely shelf environment of deposition in the two platform regions. The Amran Group has been divided into the Shuqra, Madbi and Naifa Formations (Fig. (3.10), Beydoun, 1964)) which are overlain unconformably by the Cretaceous Qishn Formation 107
  • 108. (Beydoun et al., 1993). The Shuqra Formation comprise well bedded detrital and fossiliferous limestones interbedded with marls. A rich, largely, benthonic, fauna of brachiopods bivalves, stromatoporoids, forminifera and algae together with nectonic belemnites suggest deposition in a muddy shelf environment. The overlying Madbi Formation is made up of marls (often bituminous) with shales and silty horizons and local gypsiferous units. Thin interbeds of marly and fossiliferous limestones also occur. This formation contains a rich benthonic and nektonic fauna of bivalves, brachiopods, ammonites and belemnites suggesting slightly deeper shelf environments. The lower part of the Naifa in the Eastern Platform comprise 150 to 446 m of thin-bedded fine grained limestones with thin dolomites and dolomitic shales which thicken to the west and to the northwest. The upper part contains marls, gypsiferous shales, silts and fine grained shelly limestones which locally yield a rich ammonite fauna. To conclude, the Amran is a lithologically divers group whose accumulation is largely controlled by the decrease in clastic supply during the lower Jurassic when global sea levels were rising and subtropical climate prevailed in the Arabian Peninsula. This favoured accumulation of a shallow-marine, warm-water carbonate platform throughout most of Yemen in the Oxfordian. However, there are no reports of the Amran between Al Bayda and Rada (Fig. (3.5)), a factor that may point to pre-Jurassic surface uplift in this region. Integration of fission track data with geological data (Yelland et al., 1994) indicate that part of the Precambrian basement around Al Bayda and between Rada and Marib (Fig. (3.5)) acted as topographic ‘’highs’’. Rifting of this extensive carbonate platform commenced in the Kimmeridgian with the formation of the economically important Ramlat As Sabatayn Graben which received very thick sequences of deep water and redeposited clastic and carbonate facies whilst surrounding areas continued as shallow marine platform sea-levels fall towards the end of the Jurassic resulted in restriction and evaporite deposition in Marib-Al Jawf Graben basin and the Eastern Platform and emergence and erosion of the Western Platform. Cretaceous-Tertiary: Tawilah Group The Tawilah Group outcrops over a large part of northern and central Yemen and is probably equivalent to some of the Nubian sandstones in Ethiopia and Egypt. The Tawilah Group (Figs. (3.6) and (3.12)) consists of two formations: the Ghiras formation and the Medj-zir Formation (Al Subbary, 1990; Al Subbary et al., 1993) where the later is dated as Palaeocene (op.cit.). with the extension of the Amran it is the most widely distributed sedimentary cover unit in Yemen (Robertson Group, 1992). The exposed thicknes of the Tawilah Group in western Yemen varies 108
  • 109. from 150 to 400 m with the greatest thicknesses being exposed south of Sana’a (Fig. (3.1)) (Al Subbary, 1990; Kruck and Thiele 1983). The Tawilah Group thins westwards from Sana’a to a thickness of about 200 m. The presence of thick Cretaceous sediments along the western boundary of the Ad-Dali block may point to the presence of thick Cretaceous sediments under the volcanic rocks further east (Strojexport, 1988). In the Ramlat As Sabatayn Graben up to 7,000 m of Cretaceous sands have accumulated (Bott et al., 1992) and the Cretaceous sections in the Hadramaut have thicknesses of approximately 2,000 m (Bosence, Mc Clay, Nichols and Watchorn, 1994, unpublished data). The principal lithofecies (Fig. (3.12)) are medium to very coarse-grained, trough cross-bedded sandstones which occur in decimetre to metre thick beds, sometimes amalgamated into units tens of metres thick. These sandstones are almost exclusively mature quartz arenites. Conglomerates of well-rounded vein quartz and quartzite are common at the base of thicker sandstone units and these coarse facies are interpreted as deposits from braided rivers. Thinner beds of fine sandstone and siltstone make up less than 20 % of the sequence and shales are uncommon. A prominent purple sandstone horizon up to 10 m thick is present in the Shibam area (Fig. (3.1)) and can be laterally correlated over a 100 km in an east-west direction. The Tawilah Group predominantly buff-coloured, but with a strong red or purple colouration at some levels due to high concentrations of haematite. A nodular texture, and the formation of distinct multicoloured horizons, indicates that pedogenic processes were responsible for the haematite concentrations. Lateritic paleosols are ubiquitous, and vary in thickness from less than 0.5 m to greater than 20 m. They are developed on both overbank siltstones and channel sandstones. Fluvial channel-fill sandstones are usually interbedded with the paleosols. The paleosols in the uppermost part of the Tawilah Group represent periods of non- deposition and soil development in a semi-arid environment (Fig. (3.12)). 109
  • 110. Fig. (3.12) Stratigraphy of the Tawilah Group at Jabal Marmer, Al Ghiras, Yemen (Al-Subbary and Nichols 1991; Al-Subbary et al., 1993) In eastern Yemen, the Tawilah Group may be subdivided into several formations (Beydoun. 1964). The lithofacies in these formations are varied, including shales and limestones in a predominantly siliciclastic succession. The limestones are fossiliferous, indicating a fully marine, shallow shelf environment. A shallow marine environment is also indicated by the lithofacies in the siliciclastic deposits, which show evidence for a strong tidal influence of sedimentation in shallow shelf bars, such as bi-polar cross strtification, cross-bedding reactivation surface. Towards the east, an increase is observed in the thickness of the limestone units and decrease in the grain size of the siliciclastics 110
  • 111. (Beydoun, 1964). Beydoun and Bichan (1970) reported marine Cretaceous-Tertiary sandstones and carbonates elsewhere, (e.g. island of Suqatra), where they rest unconformably on weathered basement rocks overlain by Palaeocene-Eocene limestones. Some 50 km east of Wadi Al Masila (Fig. (3.1)) the clastic sediments pinch out. In southeastern Yemen it is noted that the basal lithology is a conglomerate, when resting on the basement, and a sandstone or marl, when resting on the Amran Formation (Lobunets et al., 1988). A transition from continental to marine facies is apparent within the Tawilah Group from western to eastern Yemen (Fig. (3.13)). The eastern marine facies have been dated as Barremian-Maastrichtian (Beydoun and Greenwood, 1968) and in the Mukalla area the basal Qishn has been dated as Barremian (Beydoun et al., 1993). While Lobunets et al. (1988) stressed the lack of stratigraphically useful fossils and noted the presence of fosssil fish and petrified tree trunks, the age of the Tawilah Group can be bracketed by dating uppermost Amran using fossils and the lowermost Tertiary volcanic rocks using isotopic methods (Civetta et al., 1978). A general transition, in the environment of deposition of the Tawilah Group, from continental in the west to marine in the east (Beydoun and Greenwood, 1968) points to a regional palaeoslope (Fig. (3.13)). In western Yemen the Tawilah Group is interpreted as a sequence of braided, fluvial-channel deposits which are interbedded, in its upper sections, with ferruginous paleosol; ferricrete; horizons (Al Subbary, 1990; Al Subbary and Nichols, 1991; Menzies et al., 1992). However, a recent survey of a very large outcrop area covering at least 1,000 km2 of the Tawilah Group, between Sana’a-Al Mahwit and Taiz (Fig. (3.1)), has confirmed a general trend towards more marine influence in the east and north (Al Subbary, 1990; Al Subbary, unpublished data). Palaeocurrent data, collected from fluvial channel deposits, suggest flow to the northeast and east-northeast, consistent with the observed facies changes recorded in the southern provinces (Beydoun, 1964). Recent investigations (Watchorn, 1993 unpubl. data) suggest east to west palaeocurrent directions in the Tawilah Group of eastern Yemen. 111
  • 112. Fig. (3.13) Cretaceous-Tertiary paleogeography of Yemen (Al-Subbary and Nichols 1991 and 1993 unpublished data) In eastern Yemen, there is evidence for shallow-marine sedimentation throughout the Tawilah Group with three main carbonate incursions. This indicates that most of the Tawilah Group deposition probably took place near to sea level. East of Sana’a, agglutinated marine foraminifera have been recorded from mature sandstones and siltstones in the upper quarter of the formation (Al Subbary, 1990). In this area, large scale, greater than 5 m, cross-beds in the sandstones suggest submarine bar deposition. The coarse fluvial deposits would have been relatively rapidly deposited, so it seems likely that long periods of non-deposition, amounting to possibly tens of millions of years, may be marked by the ferricretes. This can be inferred from the age of overlying volcanic rocks which is less than 30 Ma. As a consequence of this, a considerable amount of time, Cretaceous to Oligocene, was available for deposition of less than 400 m of clastic sediment. Palaeocene- Oligocene: Hadramaut Group From the Eocene to the holocene, the western Yemen highlands were dominated by volcanic activity. In contrast, the remainder of Yemen was characterised by deposition of sedimentary rocks (Fig. (3.5)) with no evidence for volcanic detritus. Most of eastern Yemen was covered by Cenozoic sedimentary rocks during this time (Beydoun 112
  • 113. and Greenwood, 1968). These sedimentary rocks include the Palaeocene-Lower Eocene age Umm Er Radhuma Formation; Jeza Formation (Lower-Middle Eocene); the Rus, Habshiya, Qara and Andhur Formations (Middle Eocene); the Hamara Formation (Upper Eocene) and the Rimah Formation (Upper Eocene-Oligocene). The lowermost Umm er Radhuma Formation of Palaeocene- Lower Eocene age comprise shallow marine limestones, shales, marls and evaporites (Beydoun and Greenwood, 1968) with thicknesses that vary from 200 to 700 m(Agip, 1981). In eastern Yemen, it is shallow marine limestone comprising monotonous cliff forming foraminiferal grainstones. The basal Umm er Radhuma Formation contains reworked Maastrichtian fossils indicating a break in sedimentation between the Cretaceous and Tertiary in the east. Beydoun (1964) reported a disconformable contact elsewhere and, in the Hadramaut, there is evidence of large erosional breaks e.g. in Wadi Masila and near Al Mukalla with up to 600 m of erosion (Watchorn, 1993, unpublished data). The Jeza Formation overlies the Umm er Radhuma Formation conformably with either a gradational or a sharp contact, e.g. east Yemen. It consists of calcareous paper shales and well-bedded fine-grained limestones. To the east the sequence gives way to wakestones and calcareous mudstones (Robertson Group, 1992; Agip, 1981). Thicknesses increase to the south from approximately 50 m to the northeast to less than 150 m north of the Wadi Hadramaut (Braspetro, 1983; Robertson Group, 1992). The Rus Formation has gradational and conformable contacts with the underlying Jeza Formation, and comprise bedded gypsum and anhydrite with bands of chert, marl, gypsiferous chalk, dolomitic limestone and siliceous diatoms. Becouse of the restricted basinal environment of deposition, there are local facies and thickness changes in this unit. Furthermore it pinches out to the east where carbonate sediments, indicative of open water, are indistinguishable from the underlying Jeza. Thicknesses are around 50 m reaching 200 m north of Wadi Saqhawat (Braspetro, 1983) and less than 400 m in the west Mukalla area (Fig. (3.1)) (World Bank, 1983). The Habshiya Formation, which is about 175 m in thickness and overlies the Rus Formation, consists of paper shales and chalky limestone (Beydoun and Greenwood, 1968; Braspetro, 1983). To the east the sequence is represented by chalky and nodular limestones. Recent work shows that at Ras Fartaq there is no Rus Formation and the Habshiya Formation lies directly on Jeza (Watchorn, 1993, unpublished data). The Hamara Formation comprise up to 440 m of clastic deposits and overlies the Habshiya Formation. To the east the Rimah Formation, which is 210 m in thickness, was deposited as a partial time equivalent. The Rimah Formation consists of gypsiferous sands and conglomerates (Watchorn, 1993, unpublished data). 113
  • 114. Palaeocene – Eocene: Suqatra Beydoun and Bichan (1970) described Palaeocene and Eocene strata on the island of Suqatra where the limestones are conformable on underlying Cretaceous rocks. They consist of grey limestones of shallow neritic origin with chert horizons that are uniform over the whole island. Neogene: Tihama Plain and Red Sea To date, there are no known syn-rift sediments in the highland of western Yemen (Heaton et al., 1993). While some drill holes have penetrated over 3,000 m of sediments, the oldest sediments associated with opening of the basin are interbedded clastics and carbonates. In the Zeidieh well these are dated as early to middle Miocene and they represent the earliest syn-rift deposits. Seismic data reveals a basement of tilted fault blocks infilled, locally, by a syn- rift sequence. These are overlain by undeformed syn-and post-rift sediments which dip basinwards. Unpublished BP data indicate that at the interior edge of the Tihama Plain (Fig. (3.1)) the stratigraphy passes from Recent sediments into Jurassic pre-rift sediments. Non of the offshore wells or seismic data give any insights into the nature of the syn- rift sediments. On the Ethiopian side of the Red Sea, the earliest syn-rift sediments are Upper Oligocene in age (Martini, 1971). Previous workers (e.g. Roberts and Beydoun in 1992) have classified the Miocene salt and clastics as syn-rift sediments. However, seismic data across the Tihama Plain show a marked angular unconformity between the highly rotated Mesozoic sediments and the early Miocene extrusive volcanics which indicates these sediments were deposited after the main extensional rifting episode. Hence the main salt and the overlying sediments are referred to as post-rift in this report. Above the initial post-rift deposits a basinwide evaporitic unit thickens rapidly westwards up to several hundereds of metres in the Zeidieh well, to a halitic unit more than 2,000 m thick in the centre of the basin approximately 20 to 30 km offshore. Seismic data indicate that at this point the salt is 4 to 5 km below sea level. Onshore several large salt domes reach the surface (El-Anbaawy et al., 1992), the best known being the Salif diapir where there is an important active salt mine. While Landsat data indicate that this is part of a large canopy of coalesced diapirs, offshore seismic data reveal the presence of a wide range of halokinetic structures including large detached canopies now lying 2 to 3 km above their original level (Heaton et al., 1993). The majority of offshore islands, such as the Farasan Islands, are formed on reefs built on the tops of diapirs. 114
  • 115. Above the evaporite group the post-rift stage is represented by a thick cyclic succession of mixed evaporites and clastics of mid to late Miocene age which show an increase in evaporite content from east to west. The environment of deposition suggests a relatively shallow basin with periodic connection to the ocean, filled by clastic sediments from alluvial fans and rivers to the east. Throughout this time the coastline is expected to have migrated by some 100 km from a position close to the escarpment at the eastern edge of the Tihama Plain (Fig. (3.1)) to a remnant hypersaline lake in the center of the Red Sea. Limited data suggest a dominant connection with the Mediterranean Sea. At the end of the Miocene, the African and the Arabian plates finally split apart in the southern Red Sea and active volcanism began in the center of the basin. Offshore there was a marked change in sedimentation and the final part of the post-rift phase was characterised by the development of a wide spread open marine carbonate platform with biostratigraphic linkage to the Indian Ocean. From that time until the present-day sedimentation in the Tihama Plain has continued to be dominated by alluvial-fluvial processes. Salt diapirism has continued till the present as indicated by sub-horizontal raised beach deposits overlying the Salif salt dome. Two raised beaches dipping at 10o, at an elevation of 25 m, have been dated at 3,700 m to 4,300 years using C14 dating methods on Tridacna shells (Vita Finzi, 1993 unpublished data). These deposits overlie two other raised beaches with steeper dips (28o). both of the raised beach deposits have been elevated to 25 m above sea level since 4000 BP which implies an extraordinary vertical uplift rate of 2 mm/yr equivalent to an uplift of 2,000 m per Ma. which is equivalent to a strain rate of 6x10-9s-1 for a 4 km high diapir. The offshore diapirs have up to 4 km relief which implies average growth rates of 400 m per Ma. over the last 10 Ma. This is very rapid compared to strain rates measured in other salt diapir provinces. Two factors that have contributed to this are the high heat flow on the Tihama Plain (Al Mathag No. 2 well) close to the spreading centre which make the salt layer more rheid than normal, and a high proportion of salt in the overburden which facilitates rapid deformation. Post-Miocene: Tihama Plain and offshore Drilling and seismic data reveals thicknesses of 4,000 m to 6,000 m of sediment in the Gulf of Aden, Tihama Plain and Red Sea. Early Miocene marine sediments followed by Middle to Late Miocene evaporites (5,000 m) and Pliocene clastics are to be found in the Red Sea (Robertson Group, 1992 and references therein). Quaternary: Yemen 115
  • 116. Throughout much of Yemen (Fig. (3.5)) semi-consolidated superficial deposits are reported (Beydoun, 1964, 1982; Kruck et al., 1984) and consist of a wide range of dune types, loess, wadi fill deposits, alluvial plain sediments, beach sands, sabkha deposits, lagoonal sediments, coralline and algal debris. Eocene-Oligocene: Western Yemen In western Yemen, geological evolution during the Cenozoic was dominated by flood volcanism (Fig. (3.5)) and denudation as a result of surface uplift. Much of this was synchronous with the deposition of sedimentary rocksin eastern Yemen with no recorded Tertiary volcanism. The contact between the Tawilah Group and the overlying Yemen Volcanics is of particular importance because it documents the conditions immediately prior to the onset of volcanism (Fig. (3.14)). The base of the Yemen Volcanic Group is defined by the lowermost volcaniclastic unit or volcanic rock (Al Kadasi et al., 1992). A transition zone of volcaniclastic rocks and lacustrine sediments, the Lahima member shown on Figures (3.12) and (3.14), rests disconformably on the uppermost lateritic paleosols of the Tawilah Group. The sediments are situated below the first major basalt or ignimbrite that constitutes the base of the Yemen Volcanic Group. No angular unconformities are present at the base of the volcanic pile, or within it, which clearly indicates that widespread pre-volcanic extension was limited. In western Yemen, a transition zone some 20 to 40 m thick was found around Al Mahwit (Fig. (3.1)). The lower half is comprised of calcareous siltstones with concretions, intercalated with micrites containing gastropods, ostracods and bivalves, i.e. the Lahima Member (Figs. (3.12) and (3.14)). In the upper part, the siltstones are interbedded with thin alerted basaltic flows and the upper siltstones contain detrital volcanic feldspar fragments which testify to the presence of volcanic activity. Kruck et al. (1991) refer to this transition zone as the Lahima Volcaniclastics and noted that Eocene fossils had been recovered from this zone. Near Kura’a, northeast of Sana’a, the transition zone comprises lapilli tuff, volcaniclastic sediments and chert (Al-Kadasi and Menzies, 1993 unpublished data). Some siliceous sediments also contain abundant lacustrine gastropods along with turtle bones. In contrast to the west section, there is no clear evidence of marginal marine sedimentation prior to the onset of volcanism. In southern and southeastern Yemen, Strojexport (1988) report the presence of volcanic ash layers and lapilli overlain by volcanic flows. 116
  • 117. Fig. (3.14) Stratigraphy of the Tawilah Group to Yemen Volcanics transition, Yemen (Al-Kadasi and Minzies, 1993 unpublished data) Eocene-Pleistocene: Western Yemen Cenozoic volcanism in Yemen covers approximately 50,000 km2 (Fig. (3.5)) and is part of the Yemen-Ethiopia flood basalt sequence developed in the Tertiary during the rifting of the Arabian-Nubian Shield by westward propagating Carlsberg Ridge. 117
  • 118. K-Ar data indicates that Oligo-Miocene flood volcanism may have commenced as early as 45 Ma but was particularly vigorous between 31 and 20 Ma (Civetta et al., 1987; Al Kadasi, 1993 unpublished data) (Fig. (3.15)). 40Ar/39Ar studies (Zumbo et al., 1994), in conjunction with published K-Ar data, point to possibly four magmatic episodes: (1) widespread Oligo-Miocene flood magmatism(Civetta et al., 1987; Chazot et al., 1991; Menzies et al., 1992; Chazot and Bertrand, 1993; Al Kadasi, 1993 unpublished data); (2) restricted Late Miocene volcanism near Al Mokha, northeast of Sana’a and Sadah (Capaldi et al., 1987); (3) localised Pliocene volcanism at six eruptive centres along the southern coast of Yemen (Dickinson et al., 1969); and (4) discrete Plio-Quaternary alkali basalt magmatic fields throughout Yemen (Simkin et al., 1981). Volcanism was temporally and spatially associated with the formation of the Gulf of Aden and Red Sea rift systems but is unusually intense in Yemen-Ethiopia, at the Afro-Arabian triple junction, compared to the rest of the rift margins. This led to the inference that a hot mantle plume, presently located beneath Afar, was responsible for voluminous flood magmatism and perhaps rift development (White and McKenzie, 1989).flood volcanism was contiguous with formation of the vast volcanic pile developed in Ethiopia and has an estimated volume of 350,000 km3 (Mohr, 1991). Magma eruption rates in Ethiopia-Yemen are believed to have been lower (less than 0.05 km3/yr) than that of other continental flood basalt provinces (e.g. Deccan and Parana; greater than 3 km3/yr) associated with mantle thermal anomalies. Potasium-argon ages of basal basalt flows, resting disconformably on lateritic paleosols suggest that volcanism commenced around 45 to 30 Ma in Southern Yemen and 27 to 24 Ma in central and northern Yemen (Fig. (3.15)). The spatial distribution of basal K-Ar ages may imply that the locus of volcanism progressively migrated from south to north, or that peak magmatism at 27 to 24 Ma, in the south sent more voluminous flows to distal central and northern Yemen as the volcanic field developed (Menzies et al., 1993). Volcanics products include the complete spectrum of basaltic lithologies, and silicic ignimbrites and tuffs (Fig. (3.16)). Rhyolitic-ignimbrites units tend to be more common in the upper part of the volcanic stratigraphy (Fig. (3.16)), particularly near the northern periphery of the flood volcanic field (Fig. (3.5)) (Baker et al., 1993a,b). North-northwest trending granitoid plutons (Figs. (3.1) and (3.5)) up to 25 km across (east-west dimension) crop out sporadically along the marginal Red Sea escarpment for over 200 km (Al Kadasi, 1988; Blakey 1994) intrusive granite plutons, exhumed by post-volcanic faulting and erosion, may represent the roots of caldera centres that fed the extensive, coeval, ash-flow and fall deposits. Calderas were the source of voluminous ignimbrite and ashfall deposits that 118
  • 119. comprise a significant part of the flood volcanic section around Sana’a. K/Ar and Rb/Sr dating suggests that granites were emplaced between 21 to 23 Ma (Civetta et al., 1978; Capaldi et al., 1987), which is consistent with the eruption of large amounts of silicic volcanics in the upper part of the volcanic pile. Field mapping (Blakey 1993, unpublished data) indicates that the entire Yemen escarpment is not a continuous belt of granite plutons as indicated on previous photogeological maps (Kruck, 1984; Robertson Group, 1992) but that most of the terrane initially mapped as granite is comprised of silicic lavas. Some Tertiary granites appear to have steeply-dipping intrusive contacts with relatively little deformation of the country rocks produced by the intrusion. Sedimentary units, usually occurring as lenses a few metres thick and tens to hundreds of meters across, are exposed in many parts of the volcanic pile. These deposits are mainly calcareous sandstones, mudstones, reworked mafic and silicic volcanics, and may contain abundant silicified gastropods and plant material (freshwater). These small pods of sediment are considered to be deposits of small lakes and ponds formed in depressions on the low-relief volcanic landscape. Basaltic dykes are common in the lower part of the volcanic pile in western Yemen (Mohr, 1991). Most dykes were intruded perpendicular to the volcanic flows and were subsequently tilted by post-volcanic normal faulting of faulted along their margins. Volcanism believed to be late Miocene (12 to 10 Ma) in age, formed small basaltic plateaus and volcanic centres at Jabal an Nar (Al Mokha), Wadi as Sirr (NE Sana’a) and (Sada’h) (Fig. (3.1)) and is the least voluminous phase of Cenozoic magmatism (Capaldi et al., 1983; Manetti et al., 1991). Rock types include subalkaline basalt, hawaiite and trachyandesite. An important angular unconformity is preserved between the uppermost flows of the Oligo-Miocene flood volcanism (18 Ma) and the overlying late Miocene flows at Jabal an Nar (Capaldi et al., 1983; Manetti et al., 1991), which constrains normal faulting to have occurred between these dates (Huchon et al., 1992). Lobunets et al., (1988) reported volcanic rocks in the Shuqra volcanic field, east of Aden (Fig. (3.1)), with ages of 11 to 16 Ma and Strojexport (1988) reported Miocene volcanics unconformably overlying the older basalt-rhyolite series west of Aden. Pliocene volcanism (6 to 5 Ma) was dominated by evolved trachyandesite and peralkaline rhyolite stratovolcanoes. These volcanic centres underwent late stage caldera formation and from the remarkably linear Aden line along the southern coast of Yemen. Six volcanic centres (Fig. (3.5)) have been identified stretching 150 km eastwards from Bab al Mandab and include Perim, Jabal Khariz, Jabal Umm Birka, Ras Imran, Little Aden and Aden (Cox et al., 1969; 1993). 119
  • 120. Fig. (3.15) Histogram of K-Ar Ages for the Yemen Volcanic Group (Al-Kadasi et al., 1992; Al- Kadasi, Rundle and Menzies, 1993, unpublished data) Fig. (3.16) Stratigraphy of the Yemen Volcanics from Al Qanawis to San’a, Yemen (Baker and Menzies, 1993, unpublished data) Plio-Quaternary alkali basalt volcanism (5 to 0 Ma) has produced four major fields in Yemen: NW Sana’a- Amran; Dhamar-Rada; Marib-Sirwah, Balhaf-Bir Ali and Shuqra (2500 km2) (Figs. (3.1) and (3.5)). Minor 120
  • 121. Quaternary volcanic rocks also crop out along the southeastern coast of Yemen at Bir Ali. Volcanoes of probable Holocene age occur on the islands of Zukur and Hanish off the west coast of Yemen (Rogers, 1993). These fields are dominated by mafic alkali basalt and hawaiite magmas which from thin basaltic plateaus peppered by numerous small stratovolcanoes and scoria/spatter cones. Although some Pliocene ages have been reported for older rocks from the Dhamar-Rada field most of the eruptives are of Quaternary age (Fig. (3.1)).the most recent volcanic eruption in Yemen occurred in 1937, with an explosive felsic eruption south of Dhamar (Plafker et al., 1987). Geochemical data (Baker et al., 1993 a,b, 1994) requires much of the Cenozoic magmatism to have interacted with the lithosphere in route to the surface as they contrast isotopically with compositions of depleted asthenosphere and the Afar mantle plume identified on the Gulf of Aden ridge. Correlations between indices of fractionation and isotopic tracers of crustal contamination suggest that many of the basalts have assimilated continental crust. However, the marked bimodality (basalt+rhyolite) of the food volcanism is not the result of wholesale crustal anatexis but rather small amount of contamination of extremely fractionated basalts, and some of the basalts are more contaminated than the rhyolites. Contamination of heterogeneous continental crust affected rocks of all ages but is particularly evident in the older suite. Relatively uncontaminated basalts combine geochemical signatures that involve mantle contributions from depleted asthenosphere, Afar plume and, rarely, lithospheric mantle. The relative contribution of the mantle components fluctuated temporally and spatially. However volumetrically, most of the magmas are the product of decompression melting of upwelling depleted asthenosphere entrained in the Afar plume, although the HIMU-like (radiogenic Pb isotopes) Afar plume does become an important component in the post-10 Ma volcanics. 3.4 STRUCTURE AND TECTONICS OF YEMEN The tectonic architecture of the Republic of Yemen is characterised by large Archean-Proterozoic basement blocks transected by the north-west-southeast trending Jurassic-Cretaceous intracratonic rift system of the Ramlat As Sabatyn Graben, bordered to the south and to the west by Tertiary to present day Gulf of Aden and Red Sea rift system (Figs. (3.5) and (3.17)). The structure is discussed under several headings based on the subdivisions of the Robertson Group (1992). Central Block. This block comprises Precambrian areas bounded by the Red Sea faults, the Ad Dali Graben (Fig. (3.1)) and the northern and southern edges of the 121
  • 122. Ramlat As Sab’atayn Graben fault (Fig. (3.5)). Recently, the World Bank (1983) completed a comprehensive account of the structure of southern and eastern Yemen and noted that the Yemen Block was a major structural feature, and roughly coincides with the basement outcrop in Figures (3.2) and (3.4). The presence of this block of continental crust explains why Phanerozoic sedimentary formations thicken northward and eastward to Saudi Arabia and Oman. The Precambrian basement is characterised by north-south faults in the Sa’dah area and northeast-southwest faults in the Al Baydah area (Fig. (3.3)). A highly compressed fold structure with isoclinal folds is common in the Precambrian basement around Al Baydah (Figs. (3.1) and (3.3)). Between such areas there are broad antiforms and synforms characterised by more open folding. Some basement faults or shear zones may be long lived and may have undergone reactivation in Phanerozoic times producing the bounding faults of the Ramlat As Sab’atayn Graben (Robertson Group, 1992). Fission track dating (Yelland et al., 1994) in part supports this suggestion with marked contrasts in FT dates and track length distribution data across basement lineaments of Gondwana and Jurassic age. NW Block. This zone (Fig. (3.17)) is outside the region of Mesozoic and Tertiary extension and is characterised by sedimentary rocks with a poorly defined fracture pattern related to reactivation of Precambrian (Fig. (3.3)) and Jurassic trends (Fig. (3.17)). Ordovician and Permian fluvial and glacio-lacustrine elastics are the only sediments, i.e. Wajid and Akbra Formations deposited and preserved on the basement from the end of the Precambrian to the middle Jurassic- a period of no significant tectonic movements. At this time, the area was a stable block where climate controlled erosion and deposition rather than tectonics (Robertson Group, 1992). Ramlat As Sab’atayn Graben. The north-west trending Jurassic-Cretaceous rifts (Fig. (3.17)) that cut the Pan-African basement form distinct extensional fault bounded grabens with some 5,000 m thickness of Jurassic through to Tertiary carbonate and clastic rocks (Maycock, 1993) (Fig. (3.5)). The northwest trend in these grabens probably reflects reactivation of Proterozoic lineaments (Fig. (3.3)) that extendsoutheastwardss into Yemen from Saudi Arabia (Andre, 1989). The border faults to the rift are exposed on the southwestern margins of the grabens but the northeastern border faults are buried under Tertiary to Recent sediments of the Rub al Khali. The Mukalla high and the Aden high (Fig. (3.9)) are to be found to the east and west of the Ramlat As Sab’atayn Graben and sedimentological data indicates that these areas were largely emergent in pre-Jurassic times (Bott et al., 1992). The Al Mukalla high is devoid of Jurassic rocks with Cretaceous resting on Proterozoic basemen and much of the Archean- 122
  • 123. Proterozoic basement between Al-Baydah and Rada (Figs. (3.1) and (3.17)) is similarly lacking in Jurassic or more recent sediments. To some extent fission track analysis (Yelland et al., 1994) verifies that this region has been uplifted for several hundred million years (Fig. (3.18)). Fig. (3.17) Tectonic feature of Yemen (McClay 1993, unpublished data) Fig. (3.18) Distribution of apatite fission track ages from Yemen Apatites were extracted from outcroping gneissic basement and Paleozoi Mesozoic sediments (Yeland et al., 1994, Yeland et al., 1994 unpublished data) Gulf of Aden. Parts of Yemen are characterised by tectonic features that affect areas marginal to the Gulf of Aden with a north-south extensional regime related to separation of Yemen from Somalia. The fractures trend to be parallel 123
  • 124. to the Sheba ridge in Gulf of Aden and are therefore not parallel to the present coastline (Robertson Group, 1992) (Fig. (3.17)). A wide zone of crustal extension developed with east-west oriented, in some instances down to the north, domino-style tilted fault blocks. Syn-rift sedimentation of the Shihr Group is characterised by up to 3 km thickness of clastics grading upwards into carbonates. True sea-floor spreading associated with the Sheba Ridge probably only began in the Miocene (10 Ma-anomaly 5). Rift shoulder uplift probably began at around 16 Ma and resulted in significant erosion of the rift flanks with Cretaceous strata being exposed in the deepest wadis. Inland, away from the rift shoulder, gentle warping and minor faulting of Palaeocene and younger strata indicates limited reactivation of the Jurassic-Cretaceous rift structures by the Gulf of Aden rifting. Ad Dali Graben. The north-west trending Ad Dali Graben is a failed section of the Gulf of Aden-Red Sea Rift system (Fig. (3.17)) produced during the early stages of opening of the Gulf of Aden-Red Sea (Southwest-northeast extension) (Strojexport, 1988; Robertson Group, 1992). The Ad Dali Graben is out by north-west-southeast extensional fractures, which eventually became the locus of continental break up. Red Sea Rift Basin. The main extensional episode related to Red Sea rifting took place soon after deposition of some of the youngest Yemen volcanics. On the Tihama Plain, these are unconformably overlain by mid-late Miocene clastics and evaporites dated at approximately 10 Ma (Huchon et al., 1992). The amount of upper crustal extension can be estimated assuming a domino style of rotated fault blocks (e.g. Davison et al., 1994) and stretching over an area 75 km wide. An original fault dip angle of 60 to 65o is estimated from the observed bedding/fault plane cut off angles in outcrop, which gives an extension factor Β = 1.6- 1.8, calculated with the average measured bedding dip of 35o. A slightly smaller Β factor of 1.6 has been calculated in the Bajil area (Fig. (3.1)) from the average bedding plane dip of 28o. This gives an average extension rate of 4 to 5 mm per year. Historical and global teleseismic records indicate that medium magnitude earthquakes swarms are still common in Yemen because a small amount of onshore extension is continuing to this day (Ambraseys and Melville, 1983; Plafker et al., 1987). The last important earthquake occurred in 1982 in the Shamar area (Mb=5.7) where approximately 1,900 people were killed, and in 1991 at Al Udain (Mb=4.5) which caused severe damage to property. 3.5 SURFACE UPLIFT AND DENUDATION 3.5.1 Sedimentological Evidence for the Uplift History 124
  • 125. Sedimentology provides limited evidence for major changes in relief on the Red Sea margin during pre-Jurassic to early Tertiary times. The presence of paleosols at the top of the Tawilah Group prior to eruption of volcanic rocks, no marked erosional periods within the sequence, and little evidence for major ecstatic sea-level changes, i.e. greater than 100 m, suggest that uplift was minimal during pre-Oligo-Miocene times. Hughes and Beydoun (1992) note that a period of post-Eocene subsidence developed along the Red Sea margin in the late Oligocene, a period of voluminous magmatism in western Yemen. Palaeocurrent data within Jurassic-Recent sediments show no systematic change in drainage patterns that may suggest any differential uplift and denudation (Fig. (3.13)). In the Palaeocene-Eocene, the shoreline was located further west and by the lower Oligocene the onset of the major volcanism heralded the end of much of the sedimentation in western Yemen. None of these data indicate radial drainage or a temporal change to drainage consistent with lithosphere doming prior to Oligo-Miocene volcanism. Significant pre-Oligocene surface uplift is rather unlikely because of the lack of widespread extensional structures in the Phanerozoic sedimentary units of Yemen and Saudi Arabia (Almond, 1986; Menzies et al., 1992; Davison et al., 1994). This is consistent with observations in Egypt, Saudi Arabia and Ethiopia (Baldridge et al., 1991; Bohannon et al., 1989, Civetta et al., 1978; Chiesa et al., 1989; Hart et al., 1989; Mohr and Zanettin, 1988; Omar et al., 1987; Ressetar et al., 1981). Domino fault blocks in western Yemen, exposed on the Tihama Plain, displace basement, Palaeozoic-Mesozoic sediments and Tertiary volcanics indicating a significant amount of post-Oligocene-Miocene structure. In southern and eastern Yemen, differential surface uplift may have elevated crust to a position such that certain sedimentary units are absent or lack lateral continuity. In Yemen several works (e.g. Agip, 1981) have argued that the Amran limestone were deposited over most of Yemen. In contrast, recent work by Christmann et al. (1984) indicates that this might not be the ease. In west central Yemen, the area rounded by Rada, Al Baydah and W.Siham (Fig. (3.1)) is believed to have remained emergent throughout the period of Amran deposition (i.e. Jurassic). Several other areas lacking Amran are to be found in Wadi Jawf (Christmann et al., 1984) and around Al Mukalla (Fig. (3.1)) (Beydoun 1964; Agip, 1981). These authors have suggested that these areas were uplifted and that pre-Cretaceous sediments were removed by erosion or that they were uplifted in pre-Jurassic times and remained elevated for some time (Figs. (3.5) and (3.17)). A period of late Eocene uplift and erosion can also be identified in southern and eastern Yemen (Bott et al., 1992); Hughes and Beydoun, 1992) prior to development of the proto Gulf of Aden rift. 125
  • 126. 3.5.2 Fission Track Analysis of the Exhumation History Surface samples of Archean basement, Mesozoic sediments and Tertiary igneous rocks from Yemen (Figs. (3.3) and (3.5)) provide a basis for a regional analysis of the spatial variations in exhumation (Yelland, Hurford and Menzies 1993, unpublished data) and also indirect information about surface uplift (England & Molnar, 1990; Brown, 1991). Previous studies of exhumation of the Red Sea flanks, using fission track data, have highlighted relatively late exhumational cooling, post-dating major magmatic events (Sinai; Kohn & Eyal, 1981, Garfunkel, 1988, Egypt; Omar et al., 1989, central-eastern Red Sea; Bohannon et al., 1989). Throughout Yemen, it is predicted that exhumation will decrease from west to east across the rift-flank into the more stable intraplate regions. Provisional fission track data from the western rift escarpment shows a strong cooling event at ¬16 to 17 Ma (Menzies et al., 1992; 1993; 1994), probably related to exhumation of an elevated proto-Red Sea rift-flank by either tectonic or erosional processes (Fig. (3.18)). Eastwards from the Red Sea along the Gulf of Aden margin track length data indicate less exhumation. The relatively rapid cooling of the Aswad horst proximal to the Jurassic Balhaf Graben (Fig. (3.18)) indicates an interesting anomaly within the regional track length data. Exhumation information obtained from surface fission track data provides important insights into the magnitude of lost crustal section and to the thermal maturity of the subjacent rocks. In addition, fission track data support the assertion that the region around Al-Baydah and Rada (the Aden uplift) was uplifted in pre-Cretaceous times (Fig. (3.18)). 3.5.3 Geomorphological Evidence for uplift and Denudation History Fission track provides an important insight into the rate of exhumation of crustal rocks, but does not fully resolve the rate of uplift of the region without the rate of denudation being resolved from the exhumation rates. This is particularly difficult because calculations of denudation rates from contemporary studies are few in arid environments and no data exists for Yemen. Western Yemen has undergone progressive uplift and as the Yemen Plateau became higher it cooled, a function of the environmental lapse rate, the blocking and deflection of air masses, and changing palaeolatitude due to continental drift. Little assessment of the climatic change during the late Cenozoic has been undertaken in Yemen, although it is generally excepted that the glacial stages were more arid than interglacial stages, with a greater expansion of deserts and sand sheets during glacial periods (Sarnthein, 1978; Messerli et al., 1986). 126
  • 127. Nevertheless, as a result of the law latitude of Yemen throughout late Cenozoic times climatic fluctuations would have been somewhat buffered, and the present day setting provides a relatively good analogy to the past geomorphological setting. Today, the climate is arid, varying spatially due to topographic effects, with air masses forced up over the Yemen Plateau producing rain. This results in strong precipitation contrasts throughout Yemen with less than 80 mm/yr. rainfall occurring along the coastal plains and greater than 800 mm/yr. over the high mountains (Fig. (3.19)). Rainfall is sporadic with most rainfall occurring during the summer months and temperatures vary with altitude, from a mean temperature range of 25oC (January) to 39oC (July) near sea level on the Tihama Plain, to 12oC (January) to 22oC (July) on the plateau around San’a. The region has a large moisture deficit with potential evapotranspiration as high as 1,825 mm per year on the Tihama Plain (Hindorf et al., 1978; Remmele, 1989). Climate is probably the most important control on the rate and magnitude of denudational processes. Lithology is also an important control on the degree of denudation, but this is not very important when considering the region as a whole. As a result of the present climate and vegetation, Hortonian overland flow processes dominate with common flash floods. These lead to intensive erosion of bedrock and weathered regolith, and transportation of sediments out of the mountains onto the Tihama Plain. The present drainage system is strongly controlled by structural geology and lithology (Davison et al., 1994). In western Yemen, preliminary work by Owen (1993 unpublished data) using geomorphological indices and streamline surface maps shows that there is a strong relationship between geological structures and surface uplift. On the bases of geomorphological character, western Yemen can be divided into three main regions: the Tihama Plain: the Great Escarpment; and the Yemen Plateau (Fig. (3.20)). The Tihama Plain comprises a 40 km wide plain trending north-south and rising regularly from the Red Sea to an altitude of approximately 200 m in the east, where it is bounded by the Great Escarpment. The plain is drained by ephemeral streams, which flow westward and split up into complex distributaries, characterised by streams with discharges that become progressively less down stream as water percolates into the high permeable post-rift deposits of the Tihama Plain. The Great Escarpment trends NNW-SSE and can be traced from southwestern Yemen northwards for over 1,000 km to east of Makkah in Saudi Arabia and intermittently northwards for approximately another 1,000 km to Gulf of Aqabah. This is the most striking topographic feature of the Red Sea margin, rising abruptly from an altitude of approximately 200 m to more than 1,000 m above sea level. The origin of the escarpment is complex; sometimes it is produced by a series of 127
  • 128. extensional fault terraces, which gradually step down towards the Tihama Plain, but it can be also due to resistant granites and porphyritic acid lavas which are less eroded than the surrounding rocks and sediments. Individual fault scarps, bordering the Tihama Plain in the Bajil area, have been eroded back from their original position by no more than 1 to 2 km (Davison et al., 1994). Fig. (3.19) Annual precipitation and temperature distribution in western Yemen (Menzies, et al., 1994; after Dequin, 1976) 128
  • 129. Fig. (3.20) Geomorphological profile across western Yemen (Menzies, et al., 1994; after Davison et al., 1994) Beyond the Great Escarpment the rift mountains of northwestern Yemen from a broad plateau with an average elevation of approximately 2,200 m above sea level and a maximum altitude of 3,360 m at Jabal Nabi Shuyab. This high area correlates closely with the present outcrop of the Tertiary volcanics, which suggests that the high ground is related to the piling up of thick volcanics on the continental crust coupled with enhanced heat flow. Deep valleys containing ephemeral streams and rarer perennial streams whose configuration is controlled by the dominant structures traverse the region. 3.6 GEOLOGICAL HISTORY Archean and Proterozoic Gondwanaland. Magmatic arc and fore-arc complexes were accreted onto Archean cratonic nuclei and the closure of ocean basins led to incorporation of aphiolite terranes. The end of the Proterozoic was marked by intraplate extension and associated magmatism. Palaeozoic sedimentation. In the late Precambrian, the basement underwent erosion such that the resultant peneplain acted as a relatively inert basement for deposition of a generally thin Palaeozoic-Mesozoic epicontinental sequence (less than 1,000 m). Emergent landmasses in the south acted as source regions for the Wajid sandstone. Glacial material (Akbra) was deposited toward the end of the Palaeozoic in a lacustrine to shallow marine environment. A period of non-deposition occurred before and after deposition of the Permian age Akbra Shale. Mesozoic break-up of Gondwanaland. From the Permian to Jurassic there was a period of non-deposition or sediments were subsequently eroded. Gondwana-related rifting formed grabens along major crustal shear zones between Arabia, Africa and India thus renewing subsidence. Deposition of the continental early, Jurassic Kohlan sandstone occurred in much of Yemen. While much of eastern Yemen was a marine shelf by the Oxfordian, fault- 129
  • 130. controlled subsidence was restricted to the Marib-Al Jawf Graben, where 5,000 m of sediments accumulated during the late Jurassic. A continental environment dominated the area by the end of the Jurassic. Uplift, erosion and cementation of the pre-Cretaceous rocks was followed by deposition of continental to marine sediments over a slowly subsiding region centred in the southern Arabian Plate. In western Yemen continental fluviatile sandstones were deposited (Tawilah) and, in eastern Yemen, a mixture of shallow marine calcarenites and sands. Between these extremes a region of fluctuating shoreline existed close to the present-day Balhaf Graben. The continental sediments were exposed for an undefined period of time such that paleosols developed in pre Oligo-Miocene times. It could be argued that the marine transgressions in the Barremian-Aptian (108 to 116 Ma), Albian- Cenomanian (91 to 108 Ma) and Maastrichtian (65 to 72 Ma) heralded extension and subsidence that eventually led to the formation of the Gulf of Aden. However it is not known to what extent development of the ‘’subsiding basin’’ and the gulf of Aden are necessarily genetically related. The area became emergent and partially eroded at the end of the Maastrichtian (65 to 72 Ma) and a marine transgression occurred everywhere except in the west. Eocene times saw a broad lagoonal area in eastern Yemen and possibly sparse continental volcanism in the west. During the Oligocene most of western volcanism and emplacement of granites and eruption of felsic volcanics dominated Yemen. Today the plate tectonic of Yemen are dominated by north-eastward movement of the Arabian plate (1.6 to 2.0 cm/yr.) away from the African plate with concomitant formation of ocean crust in the Gulf of Aden and the southern Red Sea. 130
  • 131. CHAPTER 4: THE WHOLE YEMEN LITHOSTRATIGRAPHIC UNITS AND NOMENCLATURE TABLE 107 4.1 INTRODUCTION 108 4.2 STRATIGRAPHIC PRINCIPLES AND PROCEDURES: A SUMMARY 108 4.3 DEVELOPMENT OF THE LITHOSTRATIGRAPHIC UNITS AND NOMENCLATURE IN YEMEN 111 4.4 THE FIRST ELECTRONIC AND ATTRIBUTE TABLE ON THE WHOLE YEMENI LITHOSTRATIGRAPHIC UNITS AND NOMENCLATURE 122 131
  • 132. CHAPTER 4 THE WHOLE YEMEN LITHOSTRATIGRAPHIC UNITS AND NOMENCLATURE TABLE (New Table) 4.1 INTRODUCTION I am of the opinion that to solve the chronic problem related to the Yemeni Lithostratigraphic Units and Nomenclature, we must introduce the whole work done on its development. Here, I used my new classification and division to write about the whole work and the whole geological activities done on studding the development of lithostratigraphic and nomenclature in Yemen. This research study work as a result led to my new and first electronic and attribute table on the whole Yemeni Lithostratigraphic Units and Nomenclature (See Table. (4.1), attached to this study). Before, I am going to introduce this new and first table on the whole Yemen Lithostratigraphic Units and Nomenclature. I would like to acknowledge the reader of my Ph.D. Thesis on the known stratigraphic principles and procedures: related to the development of any lithostratigraphic nomenclature and also the whole previous and present activities done on the development of the Yemen Lithostratigraphic Units and Nomenclature. 4.2 STRATIGRAPHIC PRINCIPLES AND PROCEDURES: A SUMMARY Based on (Whittaker et al., 1991) Stratigraphy provides methods of analysis and interpretation, which are central to many fields of geological investigations. Lithostratigraphy (the description, definition and naming of rock units) is fundamental to all other branches of stratigraphy as it permits the correct recognition of the spatial relationship of rock units both vertically (in time) and laterally (in space) and thus promotes more accurate biostratigraphical and chronostratigraphical correlations and conclusions. Due to the North American Commission on Stratigraphic Nomenclature (NACSN, 1983) a stratigraphic unit is a naturally occurring body of sedimentary rock that is distinguished from the adjoining bodies of rock on the basis of some stated properties, principally lithological. Stratigraphic classification, therefore, provides the understanding of the geometry and sequence of rock bodies (units). Formalisation in nomenclature is particularly appropriate for units requiring stability, especially where these extend well beyond the area where they were first recognised. In consequence, formalisation should only be carried out according to established and internationally recognised rules in order to safeguard these objectives. Change for the sake of change, either in creating new formal 132
  • 133. names because of inadequacies in existing ones, or abandoning well-established existing names because they do not fully meet modern criteria, is to be avoided because it leads to instability and confusion. Apparent inadequacies not catered for are correctable by redefinition or revision. Four principal categories of Stratigraphic units are internationally recognised: lithostratigraphical, biostratigraphical, chronostratigraphical and geochronological. One of the main concern of this Ph.D. Thesis topics is to deal with the Lithostratigraphic unit and with the application of the principal rules and procedures that are to be followed in lithostratigraphical usage in Yemen, in the light of what has been stated above. I would like to drew the reader attention to referred to the North American Stratigraphic Code (NACSN, 1983) for more information and details, especially to Articles 1, 3-5, 7-20, 22, 24-25, 28 and 30. Many of the lithostratigraphic problems that arose in Yemen in recent years came about through very loose application of nomenclature rules. For this reason any summaries related on solving the above mentioned mater must be based on the North American Commission on Stratigraphic Nomenclature (NACSN, 1983) which in turn takes into account the rulings of the International Subcommission on Stratigraphic Classification (ISSC, 1976). (Beydoun, et al., 1998) i) No geological unit should be established or defined formally (or informally), unless its recognition serves a clear purpose. ii) A Lithostratigraphic unit (rock unit) is a naturally occurring body of sedimentary rock distinguishable from adjacent bodies or rocks on the basis of its stated properties, which is described and defined on the basis of its gross lithological characteristics and its inter-relations with adjacent units (Stratigraphic position). It is generally tabular, stratified and, in contrast to igneous rock units, conforms to the Law of Superposition. Stated properties include composition, texture, mineralogy, geochemistry, petrography, and general fossil content and, to varying extents, age. Additional modern properties such as magnetic signature, radioactivity, seismic velocity, further help to distinguish it. Care should be taken in defining boundaries so as to enable others to distinguish these. iii) In lithostratigraphical nomenclature a unit hierarchy exits, with the Formation as the basic unit of general, initially surface, geological work constituting the smallest, most used mappable or traceable unit (physical continuity), although this depends on the scale of the mapping continuity of exposures or control points. A Formation may stand- alone or several may form a group, and it may be divided into smaller divisions called Members, which commonly 133
  • 134. wedge out but possess distinctive lithologies. Individual lithostratigraphic units may be diachronous and are defined/described independently from time concepts and independently from inferred geological history. iv) In defining and describing establishing, revising, redefining or abandoning formal units, certain procedures have to be followed which include publication with a clear statement of intent (to define, revise, etc.) in a recognized scientific medium that must be readily available. v) Publication should include the following principal requirement: • Name: a geographic name combined with rank or descriptive term (capitalized), the name being chosen for uniqueness and convenience in usage. (The same name for different units-homonym-or different names for the same unit-synonym-must be avoided). A name should not be modified without explaining the need for this, precision by redefinition being preferable to abandonment. Thus, priority in publication must be respected, particularly as preservation of established name leads to stability of nomenclature. Priority on its own, however, does not justify displacing a well-established name by one neither well known or commonly used, nor does an inadequately established name need to be preserved because of priority. • Stratotype: a type section or locality with exacts geographic coordinates; this is essential to ensure accessibility for study by others. A subsurface type section in a borehole or an oilfield (names after a nearby geographic feature) is acceptable if there are no appropriate surface exposures, provided borehole rock and fossil samples are stored for public availability at an appropriate accessible repository, and borehole geophysical logs are also made accessible. All other criteria for a surface type section apply for a subsurface one. A Stratotype once properly established should never be changed although additional reference sections to supplement or illustrate critical features not evident or inadequately demonstrated at the original Stratotype, including boundary contacts, may be selected. • Description of distinguishing lithological characteristics. These include internal variations, dimensions, shape and other regional aspects, thickness at the type section and elsewhere and, as a useful characteristic, age based on fossil content or other criteria, and correlation. History or environment of deposition is valuable additions although they may play no role in the definition of a unit (only objective data are used in definition). They constitute, however, observations and inferences bearing on genesis and should be discussed at they are of value in regional understanding. 134
  • 135. vi) Revision or abandonment of formally defined and named units requires as much justification as establishment of a new unit. Redefinition, however, may be undertaken in order to change a view or emphasize content without a change in rank or in boundaries; redescription expands or corrects an inadequate or inaccurate former description. Neither of these is considered revision, hence it is possible to undertake either without the application of the stringent requirements for revision. vii) Instrumentally defined units (i.e. based on borehole geophysical logs/remotely sensed physical properties) are always considered informal. Most economically exploited units are in this category unless they are shown to be important in the elucidation of regional stratigraphy, in which case they may receive formal status by being named according to the rules summarized above. viii) A marker-defined unit or format (Forgotson, 1957) is also informal and applies to operational units representing strata sandwiched between observable markers considered as isochronous surfaces, irrespective of the spatial lithological changes in between these. Formats are useful for correlation, especially in the subsurface where they can provide a lateral link between different units of formal stratigraphy. 4.3 DEVELOPMENT OF THE LITHOSTRATIGRAPHIC UNITS AND NOMENCLATURE IN YEMEN According to my classification and division to the geological research history work in the Republic of Yemen to four stages, (Nedham M Darsi, 2000). We can record and notify the whole development history of the Yemeni Lithostratigraphic Units and Nomenclature as follows: On the FIRST STAGE: The First Systematic Geological Observation Stage or Carter’s Stage, (1852-1901) Although, no kind of activities done on studding and developing the Yemeni Lithostratigraphic Units and Nomenclature during this stage. It is known, that on 1852, Carter, H.J., was the first man, who made the First Systematic Account of observations at variety of selected locations along the south Arabian coast from Muscat in Sultanate of Oman to Aden in the Republic of Yemen. Note (1): On this stage various writers, who published their works mostly on the lavas of Aden, made geological observations. On 1844 Burr F. wrote a sketch of the Geology of Aden. On 1871 Mallet, F.R. wrote about the Geological Structure of the country near Aden with reference to the practicability of sinking Artesian Wells and on the 135
  • 136. same year Miles, S. B., Munzinger and Werner, M. made an account of an excursion into the interior of former South Yemen. On 1883 McMahon, C.A. wrote about the lavas of Aden. On the SECOND STAGE: The Hinterland Studies Stage, (1902-1946) On 1902, Raisin, C.A. wrote the first notes on the Geology of Perim Island, on 1907, Kossmat, F. made the First Systematic Geological Investigation of Socotra archipelago and on the next year Crick, G.C. and Newton, R.B. published their first determinations of Jurassic mollusks. On 1910, Lloyd, R.E. published observations on the sedimentary and volcanic rocks from the area between Aden and Ad-Dali and on the same year Tipper, G.H. and Vradenberg, E.W. respectively publishing paleontological and petrologic determinations of Lloyd's sample collection. On 1912, Botez, G. carried out the first Hydrogeological studies in the sector between Hodaida and Sana’a. The most important thing happened during this stage, that Lamare, P. (1923) made the First Lithostratigraphic Accounts of the sedimentary successions in accordance to his First Systematic Geological Investigation on the southwestern and central parts of former North Yemen. On the same year Roman, O. (Rotman) carried out first petrologic studies on the samples, that Botez, G., had collected. Also, Little, O.H. (1925) carried out a through geological reconnaissance of the Mukalla hinterland in the coastal and plateau region. On 1929, Rathjens, C. and Von Wissmann, H. carried out more regional geographical /geological/ cartographic investigations in various sectors of the interior of Yemen. On the next year, Basse, E. made a specific reference to the western part (the high plateau) augmented by paleontological determinations and on 1932, Carpentier, C. published paleontological determinations. On 1939, Gardner, E.W. wrote an article on Climate, Irrigation and Early Man in Hadhramawt with Caton-Thompson Group. Note (2): Although Lamare (1930) established well names for former North Yemen. It was so clear, that on The First stage, (the First Systematic Geological Observation Stage or CARTER, H.J. Stage) and the Second Stage (The Hinterland Studies Stage) early maps were based on photographs and on isolated visits generally to the coastal region. The geologic and the stratigraphic relations in the region are complex and it must be realised that it was not until after the Second Stage or the Hinterland Studies Stage that it was possible to compile of the region. 136
  • 137. On the THIRD STAGE: The First systematic more detailed Stratigraphic and Geological Studies Stage or Beydoun, Z.R., 's Stage, (1947-1967) On this stage more regional, extensive and relatively detailed investigations have taken place covering most aspects of geological studies, where a great number of stratigraphic sections were measured and a considerable number of field samples collected for palaneontological, microfacies study, geological and photogeological mapping. On 1947, Thesiger, W. wrote about his Journey to the Southern Arabia and the Empty Quarter. Wetzel, R., started the field-based geological mapping and stratigraphic description on 1947-1948. On 1948-1950, Morton, D.M. with Wetzel, R. continued the same work, concentrated mainly on the southern part of Mahra with some work near Mukalla, in Wadi Hadhramawt and they also carried out work on the salt dome of Bayhan. On the same year, Heybroek made reconnaissance trips in the Shuqra and Dathina areas and also to the area between Aden and Dhala and on the next year, Bagnold, R.A. studied the Sand Formation in the former south Yemen. On 1952, Jaques, E. H. made a reconnaissance survey mainly in the Western Aden Protectorate (in former South Yemen), devoting considerable attention to economic mineral occurrences and wrote notes to accompany the provisional geological map of the Western Aden Protectorate. On 1953, Bunker, D.G., wrote about the southwest Borderlands of Rub al Khali. On late 1953, Beydoun, Z.R. ONE of the most famous geologists gave his time and life on studying the geology of Yemen. We (Yemeni Geologists) are highly and greatly appreciated him as brilliant mind, wrote many publication about Yemen, which distinguished services to geological exploration and research. He died on 7 March 1998 in Beirut, at age of seventy-three. On 1954, Hudson, R.G.S. published Notes on Jurassic stromatopora of former South Yemen and on the same year Lipparini, T. wrote about the geology of the southwestern part of Yemen. On 1955, Geukens, F. traveled much to former North Yemen for the United Nations Development Programs and augmented the lithostratigrafic data obtained by Lamare and his colleagues, on 1960, wrote about Yemen geology and in 1966, wrote a Professor Paper on the Geology of the Arabian Peninsula, Yemen. 0n 1958, Greenwood, J.E.G.W. carried out field investigations and photogeological mapping, mainly on basement rocks in the western part of then Aden Protectorate (former South Yemen), this work has been published as two geological map sheets on 1:250,000 scale, on 1967. 137
  • 138. On 1960, Schott, W. provided an additional observations, but of more local nature on the lithology of the stratigraphic succession, together with paleontological / palynological age dating in connection, generally with economic objectives, for the former North Yemen. One of the most important thing happened during this stage was the formalization of nomenclature according to internationally recognized rules, which took place in the same year for the area formerly known as the Aden Protectorate (‘’South Yemen’’) (Beydoun, 1964, 1966). On 1961, Bleackley, D. with Greenwood supplemented fieldwork started by Greenwood on 1958 and after that they wrote a Professor Paper on the Geology of the Arabian Peninsula, Aden Protectorate, on 1967. On the same year, Irving, A. and Tarling, T. H. made a study on the Palaeomagnetism of the Aden Volcanoes and on 1966, Gass, I.G. and Mallick; D.I.J. published a study on the Acid volcanism on the former South Yemen coast. On 1967, Bichan, H.R. was the first one, who concentrated his study principally on the basement rocks of the Socotra archipelago, which were reported on by him and Beydoun, Z.R., 1970. On the FOURTH STAGE: The Yemeni Geologists Stage (1968-until today) The Years after the independent of the two former parts of Yemen have been an eventful years on the development of the Yemeni lithostratigraphic units and nomenclature. It is known that during this stage many Yemeni Geologists, played, play and still play a great role in the geological research history work of the Republic of Yemen. On 1968, Beydoun and Greenwood published the formalized nomenclature for the whole of the Aden Protectorate in a special fascicle of volume III of the International Lexicon of Stratigraphy for Asia. The work incorporated and partly modified the semi-formally described but well established names for former North Yemen by Lamare (1930) and Geukens (1960, 1966), covering the Jurassic System (Kohlan and Amran ‘’Series’’ modified to Kohlan Formation and Amran Group) and the Cretaceous System (Taoulah ‘’Series’’ modified to Tawilah Group). On the same year Azzaroli, A. wrote about the evolution of the Gulf of Aden. On 1969, Cox, K.G. with Mallick, D.I.J. made a Study on the volcano evolution of Aden and Little Aden and on the same year Mosely, F. wrote about the Aden Traps of Dhala, Musaymir and Radfan. The exploration effort developed sporadically during the 1970s but was increasingly backed by both regional and detailed geophysical surveys by an increasing number of seismic parties. On 1970, Dubertret, L. made a review of Structural Geology of the Red Sea and Surrounding Area and on 1973, Fairhead, J.D. wrote about the 138
  • 139. Crustal Structure of the Gulf of Aden and the Red Sea. On 1978, Grolier, M.J. and Overstreet, W.C. worked on the geologic map of former North Yemen (San’a) 1:500,000 scale. On 1980, Kruck, W. worked on different geological maps of former North Yemen and he with Thiele, J. made a study on the Late Paleozoic glacial deposits. On 1982, Abou Khadrah, A. wrote about the sedimentological evolution and the stratigraphy of former North Yemen, on 1983, Aboul Ela, M. wrote about the geology of the area northwest of San’a, San’a -Wadi Zahr district and on 1984, El- Anbaawy, M.I.H. wrote a contribution to the lithostratigraphic subdivision of the Amran sequence in former North Yemen. It is so clear, that a number of attempts were subsequently made in the 1980s to formalize the Lamare and Geukens nomenclature used in former North Yemen by renaming / redefining / revising /abandoning various units in accordance with international rules, the most consistent attempt being by El-Nakhal (1987, 1988, 1990, 1996). During the period from 1984 to 1996, Nakhal, H., El- wrote about the possibilities of late Paleozoic glaciating in centered parts of former North Yemen (1984), his observations on polygonal patterns in Jurassic sandstone (Kohlan group-1985), the lithostratigraphic subdivision of Kohlan Group (1987), the stratigraphy of the Tawilah Formation (1989), about Surdud Group, a new lithostratigraphic unit of Jurassic age (1990), the earliest eruptions of the Yemen Volcanic (1991), the Pleistocene cold episode (1993), the subdivision and formal nomenclature of the Cenozoic sedimentary rocks (1993) and about the preliminary review of the stratigraphy of the outcropping Mesozoic erathem in the northern part of Yemen (1996). The stratigraphic nomenclature schemes utilized for the sedimentary column of Yemen up until the middle of the 1980s were based entirely on formal to semiformal lithostratigraphic units. Described from measured surface sections exposed mainly in the dissected and faulted shoulders of the Gulf of Aden and Red Sea Rifts and in the high plateau of the western part of Yemen for the Mesozoic and older successions (Figs. (2.1), (2.1A), (2.1B) and (2.5)). For Paleogene units, the dissected plateau tableland covering the eastern part of the country provided the type localities, whereas embayments along the Gulf of Aden and Red Sea coastal areas furnished the type localities for the Neogene sedimentary successions. Note (3): Here, I would like to draw the reader attention on the first try done by Haq and van Eysinga (1987), on doing the first historical development of stratigraphic nomenclature schemes (Figs. (4.1) and (4.2)). The above mentioned nomenclature schemes based mainly on the surface observations and subsurface well control with surface 139
  • 140. data. It is very clear, that a rapid look at Figs. (4.1) and (4.2) will illustrate the point being made, namely that one can hardly make a straight time line correlation between the same formations even in contiguous blocks of small areal extent. Fig. (4.1) Yemen: Historical development of selected Jurassic stratigraphic nomenclature schemes (Beydoun, et al., 1997; based on Haq and Van Eysinga, 1987; U= Unpublished / restricted circulation with year in circulation where known; P= Published with year publication) 140
  • 141. Fig. (4.2) Yemen: Historical development of selected cretaceous stratigraphic nomenclature schemes (Beydoun, et al., 1997; based on Haq and Van Eysinga, 1987; U= Unpublished / restricted circulation with year in circulation where known; P= Published with year publication) On 1987, Isaev, E.N. wrote about the structural-geophysical model of the basement complex of the Aden- Red Sea region. On the same year, Maycock, I.D. wrote about the exploration and development in Marib/Al Jawf area of Marib Al- Jawf Shabwa basin. And also on the same Year Al-Thour, K.A. with El- Anbaawy, M.I.H. wrote about the sedimentological evolution and sedimentology of the Salif halite and with Simmons, M.D. made a study on the Micropalaeontological biozonation of the Amran Series (Jurassic) in the Sana’a region, (1994). 141
  • 142. The situation has also been partly aggravated in two other ways. Firstly, by increased research by academics from universities within and outside the country (having little or no access to the new subsurface data acquired since the late 1980s) who carried out more detailed investigations of surface exposures in relatively small areas mainly in the high plateau, or areally disconnected investigations of varying detail over wider areas. Some of these researchers also proposed alterations to nomenclature without due regard to formal procedures while others proposed alterations or formalizations which could not take into full account the stratigraphy of the whole country becoming known from the subsurface data. Secondly, by some of the service companies and contracted groups working for operating oil companies and/or governmental agencies on specific projects such as biostratigraphic studies, geochemical source rock analysis, mineral investigations, integration of geological mapping, or hydrocarbon exploration promotion. On 1989, Husseini, M.I. wrote about the tectonic and depositional model for the Late Precambrian- Cambrian Arabian and adjoining plates and on 1991, he with Dyer, R.A. made a study on the western Rub ‘al-Khali Infracambrian graben system. On 1990, Jungwirth, J. with As-Saruri, M., wrote about the structural evolution of the platform cover on southern Arabian Peninsula (former South Yemen) and on the same year made a study on the Karst phenomena on the south Hadramawt plateau with Schramm, H. More intensive exploration activity from the 1980s, and especially during the early 1990s after unification, has gradually unraveled a complex Mesozoic tectonic history and basin evolution, the distribution and outlines of, which had hitherto been masked under the overlying tabular Tertiary blanket of sediments and/or extrusive, flood basalt’s. This tectonic evolution was principally linked to the Late Jurassic-Early Cretaceous breakup of Gondwana and was initiated along ancient lines of crustal weakness related to a basement grain developed during the final stages of cratonization of the Arabian Shield. Rejuvenation of these NW-SE and E-W oriented fracture systems during the Mesozoic breakup of Gondwana was mainly in the form of extensional polyphase tectonics. Individual basin inception has been time-staggered, with the NW-SE fracture system rejuvenation along the ancient Najd fault trend commencing in Kimmeridgian times in the Ad-Dali basin and Sab’atayn basin (Marib- Shabwa-Hajar sectors) (Beydoun et al., 1996; Ellis et al., 1996; Schlumberger, 1992). And propagating into the Belhaf basin in Cretaceous time (Beydoun, et al., 1993, 1996). 142
  • 143. By contrast, Say’un-Al Masila basin appears to have evolved principally during the Late Jurassic to Early Cretaceous with the Jeza-Qamar basin. Subsiding rapidly as a depression principally during the Cretaceous but continuing well into the Tertiary in its eastern sector (Bott et al., 1992; Beydoun et al., 1993, 1996; Redfern and Jones, 1995; Ellis et al., 1996; Jungwirth and As-Saruri, 1990). Episodic subsidence movements punctuated by sporadic and localized short pulses of inversion and erosion appear to have affected some basins or sectors of basins but there is as yet insufficient regional control to enable more specific preciseness, particularly as Tertiary movements have overprinted their signature on the earlier picture. This history of Mesozoic extension and partial inversion in basin development has given rise to considerable variations in the details of sedimentation at the local level but, nevertheless, it does not obscure overall broad patterns of sedimentation. These were, however, only very generally understood prior to subsurface exploration and even then were incompletely grasped as exploration proceeded, because of confidentiality considerations, with individual operating companies arriving at conclusions which were principally based on results within the limits of their concession area blocks and on any traded data. This, understandably, lead to the development of company-centered informal stratigraphic nomenclature schemes as mentioned before, whose principal objective was to facilitate operations within the individual company’s concession area rather than facilitating scientific research and any ultimate communication in journals. It was inevitable that such convenience approaches should result in the proliferation of expediently designed informal nomenclature schemes; these, regrettably, have been extended beyond their intended in-house usages to neighboring and distant concession areas through data exchange. Unfortunately (although again understandable in competitive hurry), in developing these various in-house schemes, only cursory lip service could be paid to comparisons with the established surface nomenclature, which was initially erected and described in order to facilitate correlation. It was either dismissed as inappropriate to the local requirements of the subsurface and substituted by locally applicable schemes (e.g. Figs. (4.1) and (4.2), Hunt Oil column) or else hurriedly amended as desired for reasons of expediency without the proper consideration of accepted international guidelines and procedures. As some operators made more successful new hydrocarbon discoveries, increased activity by hopeful newcomers resulted in further adaptations and modifications to informal in-house oriented usage. (Beydoun, et al., 1998) 143
  • 144. During the period from 1990 to 1997, As-Saruri, M. with Langbein, R. wrote about the Habshiyah Formation and the Shihr Group. The lithostratigraphic subdivision of the outcropping Late Cenozoic Shihr Group with Beydoun, Z.R., the lithology and microfacies of Umm er Radhuma, Jiza and Rus Formation with Langbein, R., the lithological- structural provinces of the basement in the central region with Wiefel, H. and so on. On 1990, Nani, A.S.O., with Haitham, F.M.S. wrote about hydrocarbon potential of the Gulf of Aden Rift, on 1993, he with Beydoun, Z.R wrote about Qishn Formation lithofacies and hydrocarbon habitat and on 1997, wrote about the Paleozoic Clastic Reservoir in Oman, Saudi Arabia and Yemen. He published more than 18 scientific articles in and outside Yemen. On the same year, Paul, S.K. wrote about the future oil province in former South Yemen, Vesolov, V.V., wrote an explanatory note to prediction mineragenic map of the southern part of the Republic of Yemen. Wienholz, R., with Weigelt, G. wrote about the Cretaceous sediments (Tawilah Group) in the Habban-Mukalla area and the development of the Tertiary in the Habban Al Mukalla area with Schuppel, D. On 1991, Mohr, P.A. made a study on the structure of Yemeni dyke swarms. On 1992, Hughes, G.W. with Beydoun, Z.R. wrote about the biostratigraphy, lithostratigraphy, and palaeoenvironment of Red Sea-Gulf of Aden and on the same year Sikander, A.H. with Beydoun, Z.R. wrote a re-assessment of hydrocarbon potential on Red Sea-Gulf of Aden. On 1994, Mattash, M.A. and Balogh, K. made a study on the K-Ar radiometric age data on Cenozoic volcanic and their associated intrusions from Yemen. On February 1995, the Yemeni Ministry of Oil and Mineral Resources with the creation by Ministerial Degree No 4 for 1995 establishing an official Yemen Stratigraphic Commission and on 1998 a Lexion of Stratigraphy for the Republic of Yemen was the outcome of the deliberations and work of the Yemen Stratigraphic Commision. (Beydoun, Z.R., Mustafa A.L. As-Saruri, Hamed El-Nakhal, Ismail N. Al-Ganad, Rasheed S. Baraba, Abdul Sattar O.Nani and Mohammad H. Al-Aawah, 1998). Note (4): In my opinion, one of the most important things happened during the Fourth Stage or The Yemeni Geologists Stage, was the Yemeni Ministry of Oil and Mineral Resources ‘s Ministerial Degree No 4 for 1995 on establishing an official Yemen Stratigraphic Commission. This wise declaration was the first step in the right direction to solve the chronic problem related to the Yemeni Lithostratigraphic Units and Nomenclature. 121 144
  • 145. 4.4 THE FIRST ELECTRONIC AND ATTRIBUTE TABLE ON THE WHOLE YEMENI LITHOSTRATIGRAPHIC UNITS AND NOMENCLATURE Based on my work experience for 8 years in the area, the huge material collected by me during my work and my research study. Especially, the following material: 1. Most of the whole publication written on the previous and present geological activities in the Republic of Yemen. (See attached references). (1852 – today) 2. Most of the material related to the eastern Yemeni province. (Beydoun, Z. R. works and especially Beydoun et al., 1998). 3. Most of the material related to the northern Yemeni province. (Geukens, 1960, 1966). 4. Pan American Hadhramawt Oil Company (the Yemeni sector of Rub al Khali basin (Thamud – Sanau areas) enclosed the last work done on the north Hadhramawt basin or the Yemeni sector of Rub al Khali basin by the P.E.B.P ’s Engineers (Petroleum Exploration and Production Board ’s Engineers). (Faisal et al., 1998) 5. Siebens work in Socotra. (Siebens, 1977) 6. Agip work in the Gulf of Aden. (Agip, (1978,1979, … 1982)) 7. A material on Tihama area in the Red Sea area. (Davison, et al., 1994, 1996; Doornenbal, 1991; … , and Beydoun, et al., 1996, 1997) 8. Braspetro company material in the Jeza area (Wadi Al-Ghyda). (Braspetro, 1983) 9. Dr. Abdul Sattar O Nani ’s Ph.D. Thesis on the North Hadhramawt area. (Especially, Nani A.S.O., 1998) 10. Technoexport material (of the former Sovit Union company, worked in Yemen) in Shabwah area of the Marib Al-Jawf Shabwa basin. (V.O. Technoexport, 1988) 11. Yemen Hunt Oil company material in Marib Al-Jawf area of the Marib Al-Jawf Shabwa basin. (Hunt Oil Company Yemen, 1992) 12. Shell company material on S1 Block. 13. CanadianOxy Company material on the Masila block area of Sey’un Al-Masila basin. (Mills, S.J., 1992) 14. Total company material on east Shabwa area. (Total Aden (Yemen), 1990) 145
  • 146. 15. My scientific papers published on the whole Yemeni geological research history work. (Nedham, M. Darsi, (2000, 2001)) 16. My scientific papers published on the oil and gas prospect in the Yemeni sector of Rub al Khali basin. (Nedham, M. Darsi, (2000)) 17. My work and research study visits to the: a. The Yemeni sector of Rub al Khali basin. (2001) b. Sey’un Al-Masila Basin (Al-Masila Block area). (1992 – 1999) c. Marib Al-Jawf Shabwa basin (Marib, Jannah and Shabwah areas). (1992 – 1999) 122 18. My personal visits to the Tihama basin (Al-Tohaita, Zabid and Al-Khawkha areas) of the Red Sea area. (1992 – 1999) 19. My born in Crater and my whole life in Aden (Aden – Abyan basin, Gulf of Aden area). 20. All the above mentioned materials plus my research study and checks for more than 210 wells drilled in the area, as a geologist who greatly and strongly interested in the subsurface geology of Yemen, especially the eastern part of Yemen which occupy more than 75% of Yemeni sedimentary cover. The first electronic and attribute table for the whole Yemen Lithostratigraphic Units and Nomenclature (See Table. (4.1), attached to this study or see the same table without the suggested lithostratigraphic coloumn on the next pages (105 - 128)) is the outcome of my work-study with the above-mentioned material. Due to my new table, it is easy now to make a straight time line correlation between some of the different formations. As with all compromises, the end result is incomplete and does not really address the problem in depth but it does constitute a step in the right direction. Note (5): This note is on the transliteration and romanization of Arabic names, where the system of romanization of Arabic names adopted in this Ph.D. Thesis and in my new table is based on the last present methods of study done for the whole area (Beydoun, et al., 1998). It is a very simpilified version of the BGN/PCGN 1956 System which has been applied in the systematic romanization of geographical names throughout much of the Middle East, and covered by published BGN gazetteers which can be referred to in the library of the Royal Geographic Society in London. Simplification has been achieved by elimination of various diacritical symbols such as cedillas, apostrophes, dots or 146
  • 147. dashes above or below certain letters to denote shortness or length of sound and aid in phonetic pronunciation, simply because these are frequently unavailable on English language-designed manual typewriters and many word processing systems. Only the raised comma, inverted or regular and used with the letters (a,i,u), respecively denotes the Arabic letter (ain) or (hamza), while certain others are expressed by a combination of two roman letters (e.g. kh for kha, gh for ghayn, sh for sheen, and so on). It is known, that all revised lithostratigraphic names in current usage in the Republic of Yemen have been modified in accordance with this revised system. Lithostratigraphic names difined outside Yemen have been retained according to the original and established spelling (e.g. Umm er Radhuma, Sudair, Qusaiba, etc.) With regard to well known place or country names such as Aden and Yemen, these have been retained because of their long-established usage, but an attempt has been consistently made to change the spelling of Sana’a to San’a which is closer to the true pronunciation, as also is Hadramawt rather than Hadhramaut. Other less well known names have also been modified where possible. Exploration well names have, on the whole, been left alone at this stage. 147
  • 148. 148
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  • 165. CHAPTER 5: SUMMARY OF STRATIGRAPHY 148 5.1 INTRODUCTION 149 5.2 BASEMENT 153 5.3 PHANEROZOIC COVER 153 5.3.1 PALEOZOIC 153 5.3.2 MESOZOIC 154 5.3.2.1 TRIASSIC 157 5.3.2.2 JURASSIC 157 5.3.2.3 CRETACEOUS COASTAL AREA 159 5.3.2.4 CRETACEOUS: HADRAMUT AREA 161 5.3.3 CENOZOIC 162 5.3.3.1 PALEOCENE-MIDDLE EOCENE 164 5.3.3.2 OLIGOCENE-MIOCENE 165 5.3.3.3 PLIOCENE – RECENT 165 5.3.4 IGNEOUS ROCKS 165 165
  • 166. CHAPTER 5 A SUMMARY ON THE YEMENI STRATIGRAPHY 5.1 INTRODUCTION The Republic of Yemen is underlain by an Upper Proterozoic to Lower Cambrian metamoprphic basement covered by unmetamorphosed Phanerozoic deposits (Fig. (5.1)). The regional distribution of the Phanerozoic cover is strongly influenced by the Hadramut Arch (Fig. (5.2)). South of this arch, no Paleozoic rocks are known, whereas to the north a more or less complete Paleozoic section was encountered in various wells. In the southern area, differentation into a western and an eastern realm was most prominent during the Upper Jurassic and Lower Cretaceous. As a result of my work done on, the new classification and division to the Geological Research History Work of the Republic of Yemen (see Chapeter 1) and my new table for the whole Yemeni Lithostratigraphic Units and Nomenclature (see Chapeter 4 and taple (4.1), attached to this study) I am shore, that a new look to the Yemeni Geology is created and a need for a summary on the Yemeni Stratigraphy is wanted. This summary of stratigraphy is based on: 1. World-wide literature search on the Republic of Yemen upto July 1997. 2. The AGIP internal Reports on eastern Republic of Yemen (1978, 1980) 3. TECTOSTRAT propritary data on the regional geology of the Arabian Peninsula and eastern- and north eastern Africa. as based on extensive literature reviews and fieldwork during the last decade Over 10 years of TECTOSTRAT theoretical and practical research on Rift Tectonics and Reactivation of basement structures LANDSAT-data interpretation of the Arabian Peninsula and adjoining areas 4. Beydoun et al., 1998. 5. Haitham, et al. 1998. 6. My new table on the whole Yemeni Lithostratigraphic Units and Nomenclature. (Table. (4.1), attached to this study) 7. My suggestion for one ideal Stratigraphic Coulmn for the whole Yemeni Formations as a result of my correlation for the whole Yemeni lithostratigraphic units and nomenclature, espicially for the whole Yemeni Formations. 166
  • 167. 8. My high interest in the subsurface geology of the whole area and especially the eastern part of Yemen, which contain ~75% of Yemeni sedimentary cover, where I made a sum of 60 maps for an area of 40.000 sq. km. (thickness and 3D maps) from the basement to the surface. (See, Figs. (5.3A), (5.3B), (5.4A), … (5.32B). 9. My personal field notices and records, which proved and suborted by my geological field work in the area as a representative for the Petroleum Exploration and Production Board, Aden Branch, Ministry of Oil and Mineral Resources. 10. Working Companies reports and materials Fig. (5.1) Simplified geological map of the southwestern part of the Arabian Peninsula 167
  • 168. Fig. (5.2) Major tectono-stratigraphic elements of the former south Yemen. 168
  • 169. 5.2 BASEMENT The Basement of the Republic of Yemen is represented by the following units (young to old): Table (5.1): Infra-Cambrian to (?) Lower Cambrian Basement Units Group Age Formation Age Ghabar Infra-Cambrian to ?Lowermost Paleozoic Harut Infra-Cambrian to ?Lower Cambrian Khablah Infra-Cambrian to ? Lowermost Cambrian. Shabb Infra-Cambrian Minhamir Infra-Cambrian Important Note: Mudayd Formation (Upper Proterozoic-Lower Cambrian) is discarded Qinab Infra-Cambrian to Lowermost Cambrian (Subsurface of Rub al Khali Basin) IMPORTAN NOTICE (1): My personal field records show that the basemen as a formation characterised by: 1. A lithology changes (Sedimentary to Metamorphic rocks). 2. A decreases in the ROP (Rate Of Penetration). 3. A decrease in background gas with an average of 2.1 API units to 0.6 API units. • See, my work result on mapping and modelling the whole eastern part of Yemen, especially Figs. (5.32A) and (5.32B) 169
  • 170. 5.3 PHANEROZOIC COVER 5.3.1 Paleozoic The Paleozoic of the Republic of Yemen is represented by the following units (young to old): Table (5.2): Paleozoic Units Formation Age Member Age Remarks Akbarah ?Lower Permian Located in the Wajid Paleozoic (Permian and older) outcrop in NW Yemen Juwayl Upper Carboniferous to Lower They are lateral Permian subdivisions of Wajid Khusayyay Devonian-Carboniferous Formation in the n Southern Flank of Qalibah Lower Silurian Qalibah Lower Rub al Khali basin. Silurian Dibsiyah Cambrian-Ordovician The Paleozoic is known only from limited well-data in the northern part of the Republic of Yemen and appears to be a continuation of the Paleozoic as developed in the neighbouring area of the Saudi Arabia and Oman. (See, my work result on mapping and modelling the whole eastern part of Yemen, especially Figs. (5.29A),(5.29B), (5.30A), … (5.31B)). The Lower and Middle Paleozoic of the southern Arabian Peninsula comprises a sequence of (epi) continental deposits, mainly sandstones and conglomerates, generally referred to as the Wajid Sandstones which may range in age between Cambrian and Permian. The equivalent of Cambrian evaporites as found towards the east of the Arabian Peninsula (Hormuz Salt) have not been found yet, but Beydoun (1982) infers such a sequence to be present in the subsurface of the eastern RY on the basis of geophysical data. The Upper Paleozoic of southern Arabia is marked by extensive glacial deposits which relate to the Dwyka glaciation of Gondwanaland in Upper Carboniferous-Permian times. In the north part of Yemen these are known as Akbra shales (tillites overlain by intercalated sandstones and carbonates) which unconformably overlie the Wajid sandstones. 170
  • 171. 5.3.2 Mesozoic The Mesozoic of the Republic of Yemen is represented by the following units (young to old): Table (5.3): Mesozoic Units Group Age Formation Age Member Age Mahra Maastrichtian Sharwain Maastrichtian Sharwayn Maastrichtian (Cretaceous) to Lower to Lower Dabut Lower Maastrichtian Campanian Campanian to Lower Campanian Both groups: Turonian Mukalla Turonian Lusb Turonian Cretaceous (?Maastrichtia n to ?Upper Cenomanian) Mahra ?Turonian to Fartaq ?Turonian to Maqrat ?Turonian to (Cretaceous) Cenomanian Cenomanian Cenomanian (to Lower (to Lower Tuhayr ?Turonian to Albian) Albian) Cenomanian Duha Suhis Cenomanian Tawilah (Maastrichtia Harshiyat Cenomanian to Sufla Cenomanian (Cretaceous) n to Lower Albian Rays Albian Hauterivian Both groups: (?Lower Albian Qishn (?Lower Albian Qishn ?Lower Albian / Cretaceous / ?Lower Aptian / ?Lower Aptian Carbonates Aptian to Barremian in the West) in the West) Qishn ?Lower Aptian in the Upper Upper Clastics West / Lower Barremian to Barremian to Barremian to Hauterivian Hauterivian Hauterivian Sa’af Lower Barremian to Lower Hauterivian Important Note: Mithaf Formation (Campanian to Albian) and Hallah Formation (Campanian to Maastrichtian) are discarded Mahra Lower Sa’ar Lower Al Ghayl Lower Valanginian (Cretaceous) Valanginian to (mainly in Valanginian to Qalana Lower Valanginian to Middle the east) Middle Upper Berriasian Berriasian Berriasian Samarma Middle Berriasian AMRAN ( Callovian) Nayfa Berriasian to Nayfa Upper Tithonian JURASSIC to Upper Breccia Lower Tithonian Cretaceous Sab’atayn Upper Jurassic (Berriasian) (Tithonian) Sab’atayn (Upper to Safir Upper Tithonian in the NW Lower) ‘’Alif’’ (Middle- Upper) Tithonian Tithonian ‘’Seen’’ (Lower to Middle) Tithonian ‘’Yah’’ Lower Tithonian Sab’atayn Upper Jurassic ‘Ayad Upper Jurassic in the (Tithonian) (Tithonian) 171
  • 172. Group Age Formation Age Member Age centre Maqah Upper Jurassic and the (Tithonian) South East Layadim Upper Jurassic (Tithonian) Shabwa Upper Jurassic (Tithonian) Madbi Middle and Lower Tithonian to Lower Kimmeridgian Madbi (Middle to Upper (Middle to Lower) (in NW) Lower) Madbi Tithonian Tithonian to Shales Kimmeridgian Harib Lower Tithonian ‘’Lam’’ Lower Tithonian Raydan Lower Tithonian ‘’Meem’’ Lower Tithonian to Kimmeridgian Haniyah Lower Tithonian to Kimmeridgian? Ayban Lower Tithonian to Kimmeridgian Madbi (Middle to Rafad Middle Tithonian (in Lower) Ma’abir Lower Tithonian outcrop) Tithonian to to ?Upper Upper Kimmeridgian Kimmeridgian Lower Lower Tithonian to Madbi Upper Kimmeridgian Shales Shuqra Oxfordian to Arwa (Upper to Middle) Callovian (it Kimmeridgian may range locally down to Bathon and up to Kimmeridgian) Kuhlan (Middle to ?Lower) Jurassic Sudair Lower Triassic to ?Lower Permian • See, my work result on mapping and modelling the whole eastern part of Yemen, especially Figs. (5.11A), (5.11B), (5.12A), … (5.28B). 172
  • 173. 5.3.2.1 Triassic The Triassic of Hadramaut area is a continuation of the Triassic of the southernmost Saudi Arabia where it comprises sandstones and shales with minor limestones and gypsum. In the coastal zone of the Republic of Yemen, the mainly Jurassic Kohlan Formation may include a basal, Upper Triassic part. 5.3.2.2 Jurassic In the Hadramaut area only undifferentiated Jurassic is known from the Jeza syncline.In the coastal area, the Jurassic comprises the Kohlan Formation transitionally overlain by Amran Group. The Kohlan Formation of Triassic(?)- Malm age has an average thickness of ca. 70m.; it comprises sandstones and conglomerates transgressively overlying Precambrian basement or Paleozoic rocks. IMPORTAN NOTICE (2): My personal field records show that Kohlan as a formation characterised by: 1. Lithological change to Sand, Shale with interbedded Limestone 2. A positive drilling break, 3. A sharp increase in gas levels 4. An average of 3.0 API unit for background gas. 5. A peak of 22 API unit was recorded at 2693m, with the following breakdown: C1 5.7 unit C2 5.1 unit C3 3.0 unit C5 1.1 unit The mainly carbonates Amran Group consists of the following formations which are all of Malm age: Top (truncated by erosion) Nayfa: limestones and marls deposited in a shilf environment, variable thickness (max.570 m) due to pre-Barremian erosion. (See, my work result on mapping and modelling the whole eastern part of Yemen, especially Fig. (5.23A) and (5.23B)). IMPORTAN NOTICE (3): My personal field records show that Nayfa, marked as two formation Nayfa ‘A’ and Naifa ‘B’, where: 1. Nayfa ‘A’ Formation: a. Consisted of Limestone interbedded by Shale. b. Background gas variable with frequent gas peaks recorded. 173
  • 174. c. An average of 5.0 API unit for background gas. 2. NAIFA ‘B’ Formation: a. An increase in background gas b. Oil shows in the limestone. Sab’atayn: (W) evaporites Madbi: (E) shales and marls with interbedded limestones; shelf envir., variable thickness of 760 m max. (See, my work result on mapping and modelling the whole eastern part of Yemen, especially Figs. (5.26A) and (5.26B)). IMPORTAN NOTICE (4): My personal field records show that Madbi as a formation characterised by: 1. The lithology change. 2. The presence of the black shale as its main lithological factor (considered as a potential source rock). 3. The increase in the rate of penetration. 4. The increase in the background gas at its top. 5. An average of 15 API for background gases. Shuqra: limestones with intercalated marls of littoral to restricted platform environment, thickness ca. 60 m. (See, my work result on mapping and modelling the whole eastern part of Yemen, especially Figs. (5.27A) and (5.27B)). IMPORTAN NOTICE (5): My personal field records show that Shuqra as a formation characterised by: 1. Changes in lithology from dark shale to limestone. 2. A decrease in the rate of penetration 3. A decrease in the background gas from its top. 4. An average of 1.5 API units for background gas. Bottom (trasitional) 5.3.2.3 Cretaceous: Coastal Area In this area the Cretaceous is represented by the Barremian –Maastrichtian Tawilah and Mahra Groups. (See, my work result on mapping and modelling the whole eastern part of Yemen, especially Figs. (5.11A), (5.11B), (5.13A), (5.13B), (5.15A), … (5.16B).The Tawilah Group is a series of dominantly clastic rocks deposited to the west 174
  • 175. of longitude 50E; the Mahra Group is dominantly calcareous and accurs east of 50E. The groups are subdived into formations as shown below: Table (5.3A): Cretaceous: Coastal Area Units Group Name Formation Name Rrmarks TAWILAH Gr. Top (disconformity) (W) Mukalla: Shallow marine- lagoonal environment max. thickness 1 km; but decreases strongly to W Harshiyat: Shallow marine-littoral sandstones with some gypsiferous shale lenses max. 300 m thick MAHRA Gr. (E) Shawayn: Limestone, shale and marl restricted shallow platform environment max. thickness: 60 m Mukalla Fm. Fartaq: Shallow marine marls and shales with interbedded limestones max. thickness > 1500 m IMPORTAN NOTICE (6): My personal field records show that Sa’ar as a formation characterised by: 1. Lithology changes to limestone. 2. The limestone as a its main contents, being dolomitic in places grading to dolomite, interbeds with frequent shale becoming thicker with depth. 3. A negative drilling break. 4. An increase in the background gas. 5. An average of background gas from 0.5 API unit at the top to 5.0 API unit at the base. • (See, my work result on mapping and modelling the whole eastern part of Yemen, especially Figs. (5.22A) and (5.22B)). IMPORTAN NOTICE (7): My personal field records show that Qishn, marked with the following members: 1. Qishn Clastic 2. Qishn Carbonate, where: 1. Qishn Clastic characterised by: a. A main section of Sandstone, streaks of Claystone and traces of Anhydrite (with a logged trace of Coal). 175
  • 176. b. Increasing of background gas levels from 0.5 to 1.0 API unit. c. A maximum of 15.1 unit (gas peak). d. the chromatographic analysis of which broke down as follows: C1 0.77 U C2 0.11 U C3 0.98 U C5 0.2 U d. A good oil show. 2. Qishn Carbonate characterised by: 1. A main section of Limestone-Mudstone to Limestone-Wackstone with thins streaks of Shale. 2. 0.1 API unit average of background gas levels. (through the whole section) • (See, my work result on mapping and modelling the whole eastern part of Yemen, especially Figs. (5.18A), (5.18B), (5.19A), … (5.20B)). IMPORTAN NOTICE (8): My personal field records show that Harshiyat as a formation characterised by: 1. A lithology changes from carbonate to clastic rocks again. 2. Inter bedded pattern of Sand / Sandstone and Claystone grading to Shale towards the base. 3. Average gas reading ranged from 0.05 to 0.06 API unit, mainly methane due to chromatographic analysis. • (See, my work result on mapping and modelling the whole eastern part of Yemen, especially Figs. (5.16A) and (5.16B)). IMPORTAN NOTICE (9): My personal field records show that Fartaq as a formation characterised by: 1. A lithology changes from clastics to carbonate rocks. 2. A main section of interbedded Limestone and Dolomite with thin streaks of Claystone. 3. 0.5 API unit of gas reading average. 4. Methane as an only constituent. • (See, my work result on mapping and modelling the whole eastern part of Yemen, especially Figs. (5.15A) and (5.15B)). 176
  • 177. IMPORTAN NOTICE (10): My personal field records show that Mukalla as a formation characterised by: 1. A thick body of Sand / Sandstone intercalated with Claystone. 2. A Coal towards its base. 3. Appearance of hydrocarbon gases. 4. Methane traces to 0.05 API units. • (See, my work result on mapping and modelling the whole eastern part of Yemen, especially Figs. (5.13A) and (5.13B)). IMPORTAN NOTICE (11): My personal field records show that Sharwayn as a formation characterised by: 1. A lithology changes from limestone to shale. 2. A section consisted of Shale with thin steaks of Sandstone and Limestone • (See, my work result on mapping and modelling the whole eastern part of Yemen, especially Figs. (5.11A) and (5.11B)). 5.3.2.4 Cretaceous: Hadramut Area In this area, the Cretaceous is divided into the following groups and formations (young to old): Top (disconformity) Aruma Formation: equivalent to the Mukalla and (probably) Sharwayn formations, thickness ca. 100 m on Hadramut Arch, increasing rapidly towards Jeza syncline. (Table (4.1), attached to this study) Unconformity Wasia Group: partly divided into - Upper Wasia group - Ahmadi and Rumaila formations - Lower Wasia group, incorporating the Mudud formation the maximum total thickness reaches about 500 m. (See, my work result on mapping and modelling the whole eastern part of Yemen, especially Figs. (5.17A) and (5.17B)). 177
  • 178. Shuaiba Formation: equivalent to the top of Qishn formation; max. thickness is 70 m. (Table (4.1), attached to this study) Unconformity Biyad (W) and Thamama (E) formations: Lateral equivalent units of which the Biyad represent the westerly clastic-, and Thamama the easterly calcareous facies; the trasition between the two lies at approximately 50E (cf. Coastal zone, previous paragraph) and the formations can be regarded as equivalent of Qishn formation. Bottom, unconformably on Jurassic or older (basement) 5.3.3 Cenozoic The Cenozoic of the Republic of Yemen is represented by the following units (young to old): Table (5.4: Cenozoic Units Group Age Formation Age Member Age Tihamah ?Holocene / Abaas Pleistocene to Kamaran ?Holocene to Pleistocene to Pliocene Pleistocene- Lower Salif (Upper to Middle) Ghawwas (Upper to Middle) Miocene Miocene Miocene Maqna Lower Miocene Zaydiyah Lower Miocene Shihr Group Pliocene to Irqah Pliocene to Upper (onshore) Oligocene Miocene Fuwwah Lower Miocene Buwaysh Oligocene Libakhah Oligocene Ayn Ba Oligocene Ma’bad Ambakhah Oligocene Shihr Group Pliocene to Sarar Pliocene to Middle Sarar Pliocene to (offshore) Oligocene Miocene Middle Miocene Taqah Miocene to Hami Lower Miocene to Oligocene Upper Oligocene Hami Lower Miocene to Ghaydah Oligocene Upper Oligocene Ghaydah Oligocene Taqah Miocene to Oligocene Yemen Important Note: Rimah Formation (Oligocene to Upper Volcanic Eocene) and Hamarah Formation (Oligocene to Upper Eocene) are discarded Majzir Paleocene-Lower Lahimah (?Oligocene Eocene to ?Lower Eocene) Hadramawt Habshiyah Middle Eocene (Lutetian) 178
  • 179. Kaninah Middle Eocene {westward lateral Mayfa’ah Middle Eocene ‘’Transitio Middle Eocene {variants nal Beds’’ Rus Lower Eocene Jiza Lower Eocene Jawl Middle Eocene Umm er Upper Paleocene Shammar Upper Paleocene Radhuma • See, my work result on mapping and modelling the whole eastern part of Yemen, especially Figs. (5.3A), (5.3B), (5.4A), … (5.10B). 5.3.3.1 Paleocene – Middle Eocene This period is represented by sediment of the Hadramut Group in both the Coastal – and the Hadramut Areas. The base of the sequence rests conformably upon the Cretaceous, but from paleontological evidence an age gap is assumed; the top is cut by erosion. The Hadramut Group as a whole is divided into the following formations (young to old): Top (erosional unconformity) Habshiya Formation: marls and shales with interbedded limestones; restricted shallow platform. Rus Formation: gypsum and anhydrite with some bands of gypsiferous limestone; tidal flat complex. Jeza Formation: shales and marls with interbedded limestones; restricted shallow platform. Umm er Radhuma Formation: limestones with interbedded marly limestones; restricted- to open shallow platform. Bottom (disconformity) • See, my work result on mapping and modelling the whole eastern part of Yemen, especially Figs. (5.7A), (5.7B), (5.8A), … (5.10B). IMPORTAN NOTICE (12): My personal field records show that Umm er Radhuma as a formation characterised by: 1. Limestone section, as a single lithotype. • See, my work result on mapping and modelling the whole eastern part of Yemen, especially Figs. (5.3A), (5.3B), (5.4A), … (5.10B). 5.3.3.2 Oligocene – Miocene 179
  • 180. The Oligocene and Miocene are represented by the Shir Group, or Gaydah formation, (See, my work result on mapping and modelling the whole eastern part of Yemen, especially Figs. (5.6A) and (5.6B)) a heterogeneous assemblage of spatially restricted deposits occurring along the present coastline and off shore. The group comprises continental, restricted- and open shallow marine deposits. Both base and top of the sequence are defined by unconformities. 5.3.3.3 Pliocene – Recent The youngest sediments are formed by a series of continental to shallow marine deposits which unconformably overlie all older deposits from Miocene to Precambrian. 5.3.4 Igneous Rocks Following the latest Pan African (early Paleozoic) intrusions, no further igneous activity is known in the Republic of Yemen until the end of Mesozoic. In late Cretaceous time, mainly mafic volcanicity began episodcally and reached a climax in the Oligocene –Miocene. These rocks are known as the Trap Series and consist primarily of fissure and vent basaltic flows. A further phase of basaltic flows and pyroclastic eruptions, referred to as the Aden Volcanic Series followed in late Miocene or Pliocene to Recent time. The rocks of this series are mainly confined to the coastal region and broken plateau edges. Associated with this volcanicity also some Tertiary granitic intrusions are known. 180
  • 181. 1.00 0.90 40 0.80 0.70 0.60 30 0.50 0.40 20 0.30 0.20 0.10 10 0.00 -0.10 20 30 40 50 60 70 Fig. (5.3A) Thickness Map for the Youngest Sediment or Formation (Layer No. 1); (Done by: Nedham M. Darsi) 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 -0.10 Fig. (5.3B) 3D Model for the Youngest Sediment or Formation ( Layer No. 1 ); (Done by: Nedham M. Darsi) 181
  • 182. 2.40 2.20 40 2.00 1.80 1.60 30 1.40 1.20 1.00 20 0.80 0.60 0.40 0.20 10 0.00 -0.20 20 30 40 50 60 70 Fig. (5.4A) Thickness Map for Sarar Formation ( Layer No. 2 ); (Done by: Nedham M. Darsi) 2.40 2.20 2.00 1.80 1.60 1.40 1.20 1.00 0.80 0.60 0.40 0.20 0.00 -0.20 Fig. (5.4B) 3D Model for Sarar Formation ( Layer No. 2 ); (Done by: Nedham M. Darsi) 182
  • 183. 1.20 1.10 40 1.00 0.90 0.80 30 0.70 0.60 0.50 0.40 20 0.30 0.20 0.10 10 0.00 -0.10 20 30 40 50 60 70 Fig. (5.5A) Thickness Map for Taqah/Hami Formation ( Layer No. 3 ); (Done by: Nedham M. Darsi) 1.20 1.10 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 -0.10 Fig. (5.5B) 3D Model for Taqah/Hami Formation ( Layer No. 3 ); (Done by: Nedham M. Darsi) 183
  • 184. 4.00 40 3.50 3.00 2.50 30 2.00 1.50 20 1.00 0.50 10 0.00 -0.50 20 30 40 50 60 70 Fig. (5.6A) Thickness Map for Ghaidah Formation ( Layer No. 4 ); (Done by: Nedham M. Darsi) 4.00 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00 -0.50 Fig. (5.6B) 3D Model for Ghaidah Formation ( Layer No. 4 ); (Done by: Nedham M. Darsi) 184
  • 185. 1.30 1.20 40 1.10 1.00 0.90 0.80 30 0.70 0.60 0.50 20 0.40 0.30 0.20 0.10 10 0.00 -0.10 20 30 40 50 60 70 Fig. (5.7A) Thickness Map for Habshyia Formation ( Layer No. 5 ); (Done by: Nedham M. Darsi) 1.30 1.20 1.10 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 -0.10 Fig. (5.7B) 3D Model for Habshyia Formation ( Layer No. 5 ); (Done by: Nedham M. Darsi) 185
  • 186. 1.60 1.50 1.40 40 1.30 1.20 1.10 1.00 30 0.90 0.80 0.70 0.60 20 0.50 0.40 0.30 0.20 10 0.10 0.00 -0.10 20 30 40 50 60 70 Fig. (5.8A) Thickness Map for Rus Formation ( Layer No. 6 ); (Done by: Nedham M. Darsi) 1.60 1.50 1.40 1.30 1.20 1.10 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 -0.10 Fig. (5.8B) 3D Model for Rus Formation ( Layer No. 6 ); (Done by: Nedham M. Darsi) 186
  • 187. 1.05 1.00 0.95 0.90 40 0.85 0.80 0.75 0.70 0.65 30 0.60 0.55 0.50 0.45 0.40 20 0.35 0.30 0.25 0.20 0.15 10 0.10 0.05 0.00 -0.05 20 30 40 50 60 70 Fig. (5.9A) Thickness Map for Jiza Formation ( Layer No. 7 ); (Done by: Nedham M. Darsi) 1.05 1.00 0.95 0.90 0.85 0.80 0.75 0.70 0.65 0.60 0.55 0.50 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 -0.05 Fig. (5.9B) 3D Model for Jiza Formation ( Layer No. 7 ); (Done by: Nedham M. Darsi) 187
  • 188. 1.70 1.60 1.50 40 1.40 1.30 1.20 1.10 30 1.00 0.90 0.80 0.70 0.60 20 0.50 0.40 0.30 0.20 10 0.10 0.00 -0.10 20 30 40 50 60 70 Fig. (5.10A) Thickness Map for Umm Er Radhuma Formation ( Layer No. 8 ); (Done by: Nedham M. Darsi) 1.70 1.60 1.50 1.40 1.30 1.20 1.10 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 -0.10 Fig. (5.10B) 3D Model for Umm Er Radhuma Formation ( Layer No. 8 ); (Done by: Nedham M. Darsi) 188
  • 189. 0.80 45.00 0.75 0.70 40.00 0.65 0.60 35.00 0.55 0.50 30.00 0.45 0.40 25.00 0.35 0.30 20.00 0.25 0.20 15.00 0.15 0.10 10.00 0.05 0.00 5.00 -0.05 20.00 30.00 40.00 50.00 60.00 70.00 Fig. (5.11A) Thickness Map for Simsima/Sharwayn Formation ( Layer No. 9 ); (Done by: Nedham M. Darsi) 189
  • 190. 0.80 0.75 0.70 0.65 0.60 0.55 0.50 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 -0.05 Fig. (5.11B) 3D Model for Simsima/Sharwayn Formation ( Layer No. 9 ); (Done by: Nedham M. Darsi) 190
  • 191. 1.80 45 1.70 1.60 40 1.50 1.40 1.30 35 1.20 1.10 30 1.00 0.90 25 0.80 0.70 20 0.60 0.50 0.40 15 0.30 0.20 10 0.10 0.00 5 -0.10 20 30 40 50 60 70 Fig. (5.12A) Thickness Map for Fiqah Formation ( Layer No. 10 ); (Done by: Nedham M. Darsi) 191
  • 192. 1.80 1.70 1.60 1.50 1.40 1.30 1.20 1.10 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 -0.10 Fig. (5.12B) 3D Model for Fiqah Formation ( Layer No. 10 ); (Done by: Nedham M. Darsi) 192
  • 193. 2.40 45 2.20 40 2.00 35 1.80 1.60 30 1.40 25 1.20 1.00 20 0.80 15 0.60 0.40 10 0.20 5 0.00 20 30 40 50 60 70 Fig. (5.13A) Thickness Map for Mukalla Formation ( Layer No. 11 ); (Done by: Nedham M. Darsi) 193
  • 194. 2.40 2.20 2.00 1.80 1.60 1.40 1.20 1.00 0.80 0.60 0.40 0.20 0.00 Fig. (5.13B) 3D Model for Mukalla Formation ( Layer No. 11 ); (Done by: Nedham M. Darsi) 2.40 2.20 2.00 1.80 1.60 1.40 40 1.20 1.00 0.80 0.60 30 0.40 20 30 40 50 60 70 0.20 0.00 Fig. (5.14A) Thickness Map for Sufla Member ( Layer No. 12 ); (Done by: Nedham M. Darsi) 194
  • 195. 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Fig. (5.14B) 3D Model for Sufla Member ( Layer No. 12 ); (Done by: Nedham M. Darsi) 195
  • 196. 2.80 2.60 40 2.40 2.20 2.00 1.80 30 1.60 1.40 1.20 1.00 20 0.80 0.60 0.40 0.20 10 0.00 -0.20 15 20 25 30 35 40 45 50 55 60 65 70 Fig. (5.15A) Thickness Map for Fartaq Formation ( Layer No. 13 ); (Done by: Nedham M. Darsi) 196
  • 197. 2.8 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -0.2 Fig. (5.15B) 3D Model for Fartaq Formation ( Layer No. 13 ); (Done by: Nedham M. Darsi) 197
  • 198. 45 1.70 1.60 40 1.50 1.40 1.30 35 1.20 1.10 30 1.00 0.90 0.80 25 0.70 0.60 20 0.50 0.40 0.30 15 0.20 0.10 10 0.00 -0.10 -0.20 15 20 25 30 35 40 45 50 55 60 Fig. (5.16A) Thickness Map for Harshiyat Formation ( Layer No. 14 ); (Done by: Nedham M. Darsi) 198
  • 199. 1.7 1.6 1.5 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 -0.1 -0.2 Fig. (5.16B) 3D Model for Harshiyat Formation ( Layer No. 14 ); (Done by: Nedham M. Darsi) 1.10 1.00 0.90 50 0.80 0.70 0.60 20 30 40 50 60 70 0.50 0.40 0.30 0.20 0.10 0.00 Fig. (5.17A) Thickness Map for Wasia Group ( Layer No. 15 ); (Done by: Nedham M. Darsi) 199
  • 200. 1.10 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 Fig. (5.17B) 3D Model for Wasia Group ( Layer No. 15 ); (Done by: Nedham M. Darsi) 200
  • 201. 1.80 1.70 40 1.60 1.50 1.40 1.30 1.20 30 1.10 1.00 0.90 0.80 0.70 20 0.60 0.50 0.40 0.30 0.20 10 0.10 0.00 -0.10 20 30 40 50 60 70 Fig. (5.18A) Thickness Map for Qishn Formation ( Layer No. 16 ); (Done by: Nedham M. Darsi) 201
  • 202. 1.80 1.70 1.60 1.50 1.40 1.30 1.20 1.10 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 -0.10 Fig. (5.18B) 3D Model for Qishn Formation ( Layer No. 16 ); (Done by: Nedham M. Darsi) 1.10 1.00 45 0.90 0.80 40 0.70 0.60 0.50 35 0.40 0.30 0.20 30 0.10 0.00 25 -0.10 20 30 40 50 60 70 Fig. (5.19A) Thickness Map for Qishn Carbonate Member ( Layer No. 17 ); (Done by: Nedham M. Darsi) 202
  • 203. 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 -0.1 Fig. (5.19B) 3D Model for Qishn Carbonate Member ( Layer No. 17 ); (Done by: Nedham M. Darsi) 203
  • 204. 2.00 1.80 45 1.60 1.40 40 1.20 1.00 35 0.80 0.60 0.40 30 0.20 0.00 25 -0.20 35 40 45 50 55 60 65 70 75 Fig. (5.20A) Thickness Map for Qishn Clastic Member ( Layer No. 18 ); (Done by: Nedham M. Darsi) 204
  • 205. 2.00 1.80 1.60 1.40 1.20 1.00 0.80 0.60 0.40 0.20 0.00 -0.20 Fig. (5.20B) 3D Model for Qishn Clastic Member ( Layer No. 18 ); (Done by: Nedham M. Darsi) 205
  • 206. 45 0.50 40 0.45 0.40 35 0.35 30 0.30 0.25 25 0.20 20 0.15 15 0.10 0.05 10 0.00 5 -0.05 25 30 35 40 45 50 55 60 65 70 75 Fig. (5.21A) Thickness Map for Biyad ( Layer No. 19 ); (Done by: Nedham M. Darsi) 206
  • 207. 0.5 0.4 0.4 0.3 0.3 0.3 0.2 0.2 0.1 0.1 0.0 -0.1 Fig. (5.21B) 3D Model for Biyad ( Layer No. 19 ); (Done by: Nedham M. Darsi) 207
  • 208. 45 2.40 40 2.20 2.00 35 1.80 1.60 30 1.40 1.20 25 1.00 20 0.80 0.60 15 0.40 0.20 10 0.00 5 -0.20 25 30 35 40 45 50 55 60 65 70 75 Fig. (5.22A) Thickness Map for Sa'ar Formation ( Layer No. 20 ); (Done by: Nedham M. Darsi) 208
  • 209. 2.40 2.20 2.00 1.80 1.60 1.40 1.20 1.00 0.80 0.60 0.40 0.20 0.00 -0.20 Fig. (5.22B) 3D Model for Sa'ar Formation ( Layer No. 20 ); (Done by: Nedham M. Darsi) 209
  • 210. 1.40 1.30 40 1.20 1.10 1.00 0.90 30 0.80 0.70 0.60 0.50 20 0.40 0.30 0.20 10 0.10 0.00 -0.10 20 30 40 50 60 70 Fig. (5.23A) Thickness Map for Nayfa Formation ( Layer No. 21 ); (Done by: Nedham M. Darsi) 210
  • 211. 1.40 1.30 1.20 1.10 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 -0.10 Fig. (5.23B) 3D Model for Nayfa Formation ( Layer No. 21 ); (Done by: Nedham M. Darsi) 211
  • 212. 0.85 0.80 40.00 0.75 0.70 0.65 0.60 0.55 30.00 0.50 0.45 0.40 0.35 20.00 0.30 0.25 0.20 0.15 0.10 10.00 0.05 0.00 -0.05 20.00 30.00 40.00 50.00 60.00 70.00 Fig. (5.24A) Thickness Map for Sab'atayn Formation ( Layer No. 22 ); (Done by: Nedham M. Darsi) 212
  • 213. 0.9 0.8 0.8 0.7 0.6 0.6 0.6 0.5 0.4 0.4 0.3 0.3 0.3 0.2 0.2 0.1 0.1 0.0 -0.1 Fig. (5.24B) 3D Model for Sab'atayn Formation ( Layer No. 22 ); (Done by: Nedham M. Darsi) 213
  • 214. 0.65 0.60 40.00 0.55 0.50 0.45 30.00 0.40 0.35 0.30 0.25 20.00 0.20 0.15 0.10 0.05 10.00 0.00 -0.05 20.00 30.00 40.00 50.00 60.00 70.00 Fig. (5.25A) Thickness Map for Lam Member ( Layer No. 23 ); (Done by: Nedham M. Darsi) 214
  • 215. 0.6 0.6 0.6 0.5 0.4 0.4 0.3 0.3 0.3 0.2 0.2 0.1 0.1 0.0 -0.1 Fig. (5.25B) 3D Model for Lam Member ( Layer No. 23 ); (Done by: Nedham M. Darsi) 215
  • 216. 1.3 1.2 40 1.1 1.0 0.9 30 0.8 0.7 0.6 0.5 20 0.4 0.3 0.2 0.1 10 0.0 -0.1 20 30 40 50 60 70 Fig. (5.26A) Thickness Map for Madbi Formation ( Layer No. 24 ); (Done by: Nedham M. Darsi) 216
  • 217. 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 -0.1 Fig. (5.26B) 3D Model for Madbi Formation ( Layer No. 24 ); (Done by: Nedham M. Darsi) 217
  • 218. 0.8 0.7 40 0.6 0.6 0.6 0.5 30 0.4 0.4 0.3 0.3 20 0.3 0.2 0.2 0.1 10 0.1 0.0 -0.1 20 30 40 50 60 70 Fig. (5.27A) Thickness Map for Shuqra Formation ( Layer No. 25 ); (Done by: Nedham M. Darsi) 218
  • 219. 0.8 0.7 0.6 0.6 0.6 0.5 0.4 0.4 0.3 0.3 0.3 0.2 0.2 0.1 0.1 0.0 -0.1 Fig. (5.27B) 3D Model for Shuqra Formation ( Layer No. 25 ); (Done by: Nedham M. Darsi) 219
  • 220. 2.2 40 2.0 1.8 1.6 30 1.4 1.2 1.0 0.8 20 0.6 0.4 0.2 10 0.0 -0.2 20 30 40 50 60 70 Fig. (5.28A) 3D Model for Kohlan Formation ( Layer No. 26 ); (Done by: Nedham M. Darsi) 220
  • 221. 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -0.2 Fig. (5.28B) 3D Model for Kohlan Formation ( Layer No. 26 ); (Done by: Nedham M. Darsi) 221
  • 222. 1.2 1.1 1.0 45 0.9 0.8 0.7 40 0.6 0.5 0.4 0.3 35 0.2 0.1 0.0 -0.1 30 -0.2 40 45 50 55 60 65 70 75 Fig. (5.29A) Thickness Map for (Permian – Triassic) Formation ( Layer No. 27 ); (Done by: Nedham M. Darsi) 222
  • 223. 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 -0.1 -0.2 Fig. (5.29B) 3D Model for (Permian – Triassic) Formation ( Layer No. 27 ); (Done by: Nedham M. Darsi) 223
  • 224. 1.2 1.1 45 1.0 0.9 0.8 0.7 40 0.6 0.5 0.4 35 0.3 0.2 0.1 0.0 30 -0.1 40 45 50 55 60 65 70 75 Fig. (5.30A) Thickness Map for the (Devonian - Carboniferous) Formation ( Layer No. 28 ); Done by: Nedham M. Darsi) 224
  • 225. 1.20 1.10 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 -0.10 Fig. (5.30B) 3D Model for the (Devonian - Carboniferous) Formation ( Layer No. 28 ); (Done by: Nedham M. Darsi) 225
  • 226. 45 2.00 1.80 1.60 1.40 40 1.20 1.00 0.80 0.60 35 0.40 0.20 0.00 -0.20 30 -0.40 40 45 50 55 60 Fig. (5.31A) Thickness Map for the Oldest Sediment or Formation (Cambrian (?) – Ordovician – Lower Silurian) ( Layer No. 29 ); (Done by: Nedham M. Darsi) 226
  • 227. 2.00 1.80 1.60 1.40 1.20 1.00 0.80 0.60 0.40 0.20 0.00 -0.20 -0.40 Fig. (5.31B) 3D Model for the Oldest Sediment or Formation (Cambrian (?) – Ordovician – Lower Silurian) ( Layer No. 29 ); (Done by: Nedham M. Darsi) 227
  • 228. 3.0 35 2.8 2.6 30 2.4 2.2 25 2.0 1.8 1.6 20 1.4 1.2 15 1.0 0.8 0.6 10 0.4 0.2 5 0.0 15 20 25 30 35 40 45 50 55 60 Fig. (5.32A) Thickness Map for the drilled parts of the Basement ( Layer No.30 ); (Done by: Nedham M. Darsi) 228
  • 229. 3.00 2.80 2.60 2.40 2.20 2.00 1.80 1.60 1.40 1.20 1.00 0.80 0.60 0.40 0.20 0.00 Fig. (5.32B) 3D Model for the drilled parts of the Basement ( Layer No.30 ); (Done by: Nedham M. Darsi) 229
  • 230. CHAPTER 6: PHANEROZOIC SIDIMENTARY SEQUENCE SUBDIVISION /STRATIGRAPHIC/SEDIMENTOLOGIC ANALYSIS 226 6.1 INTRODUCTION 227 6.2 PALEOZOIC 228 6.2.1 Lithology 228 6.2.2 Source rock/reservoir characteristics 230 6.3 TRIASSIC (?) – JURASSIC 230 6.3.1 Lithology 230 6.3.2 Source rock/reservoir characteristics 231 6.4 CRETACEOUS 232 6.4.1 Lithology 232 6.4.2 Source rock/reservoir characteristics 232 6.5 PALEOCENE – MIDDLE EOCENE 233 6.5.1 Lithology 233 6.5.2 Source rock/reservoir characteristics 233 6.6 OLIGOCENE / MIOCENE – RECENT 234 6.6.1 Lithology 234 6.6.2 Source rock/reservoir characteristics 235 230
  • 231. CHAPTER 6 PHANEROZOIC SIDIMENTARY SEQUENCE SUBDIVISION /STRATIGRAPHIC / SEDIMENTOLOGIC ANALYSIS 6.1 INTRODUCTION First of all, quick look to the pervious 60 maps done on the eastern part of the Republic of Yemen, (based on my study to the subsurface geology for an area of 40.000 sq. km), show that the eastern part of the Republic of Yemen stratigraphy seems to by comparable. Especially the same stratigraphic units deposited in the same time and having different names. This result proves and supports the work done by the International Tectostrat Geoconsultants (1987) in the Hadhramawt Region in the eastern part of the Republic of Yemen, where their study led to, that the stratigraphy of Hadhramawt Region seems to be comparable with that of the Southern Region. Based on available stratigraphic sections and well data from eastern part of Yemen, data from the southern part of eastern Republic of Yemen, i.e. The Coastal Region, have been collected by Agip during field-surveys in 1978 and 1980 (Agip, 1981; 82). Another set of data concerning the Hadhramawt Region consists of drilled well sections provided by Canadian Oxy. Based on: 1. My Lithostratigraphic Units and Nomenclature table (Table. (4.1)) supported with my ideal stratigraphic column suggested for the whole Yemen. 2. My Thickness and 3D Maps done on the eastern part of Yemen, 3. The huge material used by me during my work and study to the most of Yemeni area. All above-mentioned works, data and materials give me the whole right to introduce a new look to the area and suggest a new subdivision to the whole Phanerozoic sedimentary sequence of the Republic of Yemen. The whole Phanerozoic sedimentary sequence of the Republic of Yemen can be subdivided into five depositional sequences, i.e. from young to old: 231
  • 232. e. OLIGOCENE / MIOCENE-RECENT d. CRETACEOUS (Lower Hauterivian to Maastrichtian) / PALEOCENE – MIDDLE EOCENE c. JURASSIC – CRETACEOUS (Lower Berriasian to Lower Valanginian) b. UPPER PALEOZOIC (Devonian – Permian) / TRIASSIC (Lower Triassic) (?) a. LOWER PALEOZOIC (Cambrian (?) - Lower Silurian (Llandoverian)) This new subdivision to the whole Phanerozoic sedimentary sequence of the Republic of Yemen, particularly support the pervious subdivision done to the Phanerozoic sedimentary sequence of the eastern part of the Republic of Yemen by the International Tectostrat Geoconsultants (1987). They subdivided the Phanerozoic sedimentary sequence of the eastern part of the Republic of Yemen into five depositional sequences, from young to old. e. OLIGOCENE / MIOCENE-RECENT d. PALEOCENE – MIDDLE EOCENE c. CRETACEOUS b. TRIASSIC (?) - JURASSIC a. PALEOZOIC In the following paragraphs the general outline of the stratigraphic history of the Republic of Yemen is described on the basis of the study done by the International Tectostrat Geoconsultants (1987), these new five depositional sequences, summarised in my Lithostratigraphic Unit and Nomenclture Table, and on the sixty maps done on the eastern part of the Republic of Yemen. In that table and at those maps, depositional environment and thickness of the described formations throughout the Republic of Yemen and especially the eastern part of the Republic of Yemen are plotted in order to locate areas of subsidence and uplift. These new steps show and prove the pervious idea that the descriptions of the environment of deposition are too general especially to the eastern part of Yemen. Source rock/reservoir characteristics, as derived from the literature have been for every depositional sequence. 232
  • 233. 6.2 PALEOZOIC 6.2.1 Lithology Paleozoic sediments have been encountered in the Yemeni sector of Rub al Khali basin, north part of Yemen and on Soqatra Island (?). In the eastern part of the Republic of Yemen Paleozoic sediments have been encountered only in the subsurface of north Hadhramawt Region. Paleozoic sediments are probably of (epi) continental origin and can be correlated with the Wajid sandstones and Akbra shales found in the north part of the Republic of Yemen. Within this sequence Devonian / Carboniferous strata are cut off by Permian strata along the northern Hadramut Arch. Furthermore the whole Paleozoic sequence thickens in a northerly direction. This implies that the arch became pronounced during the Paleozoic as a result of uplift in Devonian / Carboniferous times as suggested by the International Tectostrat Geoconsultants (1987) Important Notice (1): Here, I would like to suggest a new subdivision to the Paleozoic sediments of the whole Republic of Yemen, into two depositional sequences, i.e. from young to old: b. UPPER PALEOZOIC (Devonian – Permian) / TRIASSIC (Lower Triassic) (?) a. LOWER PALEOZOIC (Cambrian (?) - Lower Silurian (Llandoverian)) Based on: 1. The above-mentioned works, data and materials, which gave me the whole right to introduce and suggest a new subdivision to the whole Phanerozoic sedimentary sequence of the Republic of Yemen into five depositional sequences. 2. The evidence of an age gap for the Middle and Upper Silurian rocks and an evidence of an age gap for the Middle and Upper Triassic rocks (?) in whole Yemen is assumed, they cut by erosion. 3. The absence of (Middle and Upper Silurian rocks) and (Middle and Upper Triassic rocks (?)) in whole Yemen reflects a period of general uplift throughout the Southwestern Arabia during above mentioned times. 4. This 2 age gaps are strongly supporting my new subdivision to the Paleozoic sediments into two depositional sequences. 233
  • 234. Important Notice (2): In my opinion, presence of Lower Paleozoic (Cambrian (?) - Lower Silurian (Llandoverian)) depositional sequence, which cut off by Upper Paleozoic (Devonian – Permian) / Triassic (Lower Triassic) (?) depositional sequence along the northern Hadhramawt Arch. Furthermore the whole depositional sequence thickens in a northerly direction. This implies that the arch became pronounced during the Lower Paleozoic as a result of uplift in Cambrian (?) - Lower Silurian (Llandoverian) times. 6.2.2 Source rock/reservoir characteristics Qalibah Formation: good source rock, often hydrocarbon smell on fresh Dependable on the intensity of the Karroo rifting, source rock potential may exist in the Permian sediments. Important Notice (3): The presence of Qalibah Formation of Lower Silurian age in Yemen has an important meaning. It is known that one of the most famous oilfield all over the world, i.e. Ghawar in Saudi Arabia and Messaoud in Algeria contain oil from Silurian source rocks. 6.3 TRIASSIC (?) - JURASSIC 6.3.1 Lithology During the lower to Middle Jurassic (possibly Late Triassic (?)) the region was transgressed from the East. The Kohlan, Shuqra and Madbi sediments were deposited in a gradually subsiding and deepening basin with uniform conditions throughout the area. Slumping features and erosional channels, which developed during Naifa sedimentation, indicate tectonic activity during the Tithonian. (See my Lithostratigraphic Units and Nomenclature table (Table. 4.1), attached to this study). A general uplift between Tithonian and Barremian times caused differential erosion, which, in general removed the entire Middle and Upper Valanginian rocks in the whole Republic of Yemen. (See the same table, (Table 4.1)) and in places (e.g. The Mukalla region), removed the entire Jurassic sequence. These data suggest that tectonic activity between Kimmeridgian and Barremian times give rise to highs and lows. 234
  • 235. During the Upper Jurassic, evaporites were deposited in the NW part of the area (Sab’atayn Formation). These sediments are exposed in salt domes, which are though to be related to the opening of the Gulf of Aden. Tectonism caused by older salt movement can not be excluded. Important Notice (4): Here, I would like to suggest the following new subdivision: c. JURASSIC – CRETACEOUS (Lower Berriasian to Lower Valanginian) Based on: 1 The above-mentioned works, data and materials, which gave me the whole right to introduce and suggest a new subdivision to the whole Phanerozoic sedimentary sequence of the Republic of Yemen into five depositional sequences. 2 The evidence of an age gap for Middle and Upper Triassic rocks (?) and an evidence of an age gap for the Middle and Upper Valanginian rocks in whole Yemen is assumed, they cut by erosion. 3 The absence of (Middle and Upper Triassic rocks (?)) and (Middle and Upper Valanginian rocks) in whole Yemen reflects a period of general uplift throughout the Southwestern Arabia during above mentioned times. 4 The presence of a depositional sequence between the above mentioned 2 age gaps is an argument of subsidence period happened in the Jurassic to Cretaceous (Lower Berriasian to Lower Valanginian) time. 5 This subsidence period prove and support the above mentioned depositional sequences suggested by me as a new subdivision. 6.3.2 Source rock/reservoir characteristics Kohlan Formation: good reservoir characteristics Shuqra Formation: fair reservoir characteristics Madbi Formation: good source rock, often hydrocarbon smell on fresh fractures Laboratory analyses show a fair amount of organic matter rich in hydrogen. Naifa Formation: may be good source rock, often hydrocarbon smell on fresh fractures Laboratory analyses show a negligible amount of organic matter. Sab’atayn Formation: good source and cap rock. 235
  • 236. 6.4 CRETACEOUS 6.4.1 Lithology A new transgression, again from the E, started in Barremian times and a wide restricted shallow platform was established (Qishn Formation). Afterwards the western part of the area was covered by mainly clastic continental to shallow marine sediments (Harshiyat Formation), while in the eastern part mainly carbonatic sediments were deposited initially on a restricted to open marine platform, later followed by deeper platform deposits (Fartaq Formation). There is a gradual transition between clastics in the W and carbonates in the E. The thick development of Fartaq Formation in the E may indicate active subsequence in this part of the area Aptian / Cenomanian times. It should be noted that the thick development includes (the eastern part of) the Jeza Syncline, where according to the literature, subsidence did not start until Oligo-Miocene times (see also paragraph 6.6.1). The Fartaq / Harshiyat sequence is overlain by clastics of the Mukalla Formation. The striking differences in thickness of this formation from area to area point to tectonic activity during the Turonian – Senonian. Shallow restricted platform sediments (Sharwayn Formation) were deposited in the eastern part of the area but are absent in the west. This may indicate subsidence of the eastern part of the area during Maastrichtian times. A general uplift ended the Cretaceous sedimentation. 6.4.2 Source rock/reservoir characteristics Harshiyat Formation: very good reservoir characteristics Fartaq Formation: may be both source rock and reservoir, some interbedded shaley layers could be considered as cap rock Mukalla Formation: very good reservoir characteristics 6.5 PALEOCENE – MIDDLE EOCENE 6.5.1 Lithology During the Paleocene the region was transgressed from the E and uniform sedimentary conditions established over the area with deposition of shallow platform limestones (Umm Er Radhuma Formation). 236
  • 237. Conditions became more restricted in Lower Eocene time (Jeza Formations), but in the easternmost part of the area no distinction is possible between the Umm Er Radhuma and Jeza Formations. This probably indicates the proximity of open sea. Complete closure of the basin towards the end of the Lower Eocene gave rise to evaporitic sedimentation (Rus Formation), but in the eastern part of the region the sediments are more carbonitic and indicate open sea nearby. In the western part of the area an anomalous thick evaporitic sequence indicates strong local subsidence. In Middle Eocene a shallow restricted platform established over the area (Habshiya Formation) until general uplift ended the sedimentary cycle. 6.5.2 Source rock/reservoir characteristics Umm Er Radhuma Formation: possible reservoir Jeza Formation: good cap rocks (shales); may be reservoir (limestones) but often has insufficient thickness Rus Formation: good cap rock; may be reservoir but often has insufficient thickness Habshiya Formation: good reservoir in the eastern part of east RY. Important Notice (5): Here, I would like to suggest the following new subdivision: d. CRETACEOUS (Lower Hauterivian to Maastrichtian) / PALEOCENE – MIDDLE EOCENE Instead of the two mentioned pervious used subdivision: d. PALEOCENE – MIDDLE EOCENE c. CRETACEOUS Based on: 1 The above-mentioned works, data and materials, which gave me the whole right to introduce and suggest a new subdivision to the whole Phanerozoic sedimentary sequence of the Republic of Yemen into five depositional sequences. 2 The evidence of an age gap for Middle and Upper Valanginian rocks and an evidence of an age gap for the Upper Eocene rocks in whole Yemen is assumed, they cut by erosion. 3 The absence of (Middle and Upper Valanginian rocks) and (Upper Eocene rocks) in whole Yemen reflects a period of general uplift throughout the Southwestern Arabia during above mentioned times. 237
  • 238. 4 The presence of a depositional sequence between the above mentioned age gaps is an argument of subsidence period happened in the Cretaceous (Lower Hauterivian to Maastrichtian) / PALEOCENE – MIDDLE EOCENE 5 This subsidence period led to the above mentioned depositional sequences suggested by me as a new subdivision. 6.6 OLIGO-MIOCENE - RECENT 6.6.1 Lithology during Oligo-Miocene a transgressive sequence of very heterogeneous shallow marine character, i.e. The Gaydah Formation was deposited. The sediments contain a large amount of eroded material from the older formations. The Gaydah Formation unconformably (often angular) overlies the Habshiya and sometimes Rus, Jeza or Umm Er Radhuma Formation. Taken together, this implies tectonic activity before deposition of Gaydah Formation and strong erosion of the older formations. In low-lying areas, corresponding to the present day coast- and offshore regions, erosion of the underlying Habshiya Formation is weak. The Oligo-Miocene strata are rapidly thickening towards the South The phenomena described above indicate a drastic change in Palaeogeography before deposition of the Oligo- Miocene sequence: strong subsidence south of the Hadramut region; uplift of northern and southern Hadramut Arch; subsidence in Jeza syncline. Deep erosion of the Oligo-Miocene strata indicates a period of tectonic activity before the deposition of the Pliocene-Recent sediments. Fissure and vent basaltic flows (Aden Trap Series) have been in- and extruded during Late Cretaceous – Oligocene – Miocene. The Pliocene-Recent sediments are transgressively and unconformably overlying Oligo-Miocene and/or older deposits. These sediments are of a shallow marine character and, according to the literature, are subhorizontal. The Aden Volcanic Series have been extruded as vent basaltic flows and pyroclastic eruptions during the Miocene to Recent. In the western part of the RY they are associated with intrusions of granites. 238
  • 239. 6.6.2 Source rock/reservoir characteristics The igneous rocks described above are not of minor importance for oil exploration due to absence of organic matter, immaturity and leaking of porous layers. 239
  • 240. CHAPTER 7: PRESENCE OF THE WHOLE EOCENE AND TRIASSIC ON THE YEMENI ISLAND OF SOCOTRA 236 7.1 INTRODUCTION 237 7.2 THE GEOLOGICAL RESEARCH HISTORY WORK OF SOCOTRA ISLAND 237 7.3 GEOLOGY OF SOCOTRA ISLAND 238 7.4 STRATIGRAPHIC SUMMARY OF SAMAH-1A 239 7.5 OIL AND GAS PREDICTION 240 240
  • 241. CHAPTER 7 PRESENCE OF THE WHOLE EOCENE AND TRIASSIC ON THE YEMENI ISLAND OF SOCOTRA (???) 7.1 INTRODUCTION The Island of Socotra is the largest and most easterly of a group of islands, which includes Abd al Kuri, Samha, and Darsa. It is located 380 kilometers south-southeast of Ras Fartaq, the closest point on the Arabian Peninsula; and 250 kilometers east-northeast of Cape Guardaful, at the northeast tip of Somalia. The surface area of the islands is about 3.650 square kilometers; a broad continental shelf area, particularly well developed on the south side, surrounds the island chain, with an area of approximately 32,000 square kilometers. (Figs. (7.1), (7.2)) For the most part, the island of Socotra is covered by a veneer of Cretaceous and Tertiary limestones, up to 700 meters in thickness, which forms an undulating, irregular, and in part block-faulted upland plateau ranging from 300 to 900 meters in elevation, overlying an older igneous and metamorphic basement. Three main structural uplift areas from the central backbone of Socotra, culminating in the spectacular Haggier Range with peaks rising to 1.500 meters. In other areas, where part of the limestone cover has been removed, recent deposits largely obscure the earlier rocks, in particular along the northern and southern coastal plains and in some of the inland depressions. 7.2 THE GEOLOGICAL RESEARCH HISTORY WORK OF SOCOTRA ISLAND 1. On the First Stage: The First Systematic Geological Observation Stage or Carter’s Stage, (1852-1901) No kind of geological activities are recorded on the above-mentioned island. 2. On the Second Stage: The Hinterland Studies Stage, (1902-1946) On 1907, Kossmat, F. made the First Systematic Geological Investigation of the Socotra archipelago 3. On the Third Stage: The First Systematic more detailed Stratigraphic and Geological Studies Stage or Beydoun, Z.R.'s Stage, (1947-1967): Z.R. Beydoun undertook the earliest systematic study of the geology of Socotra Island in 1953 for the Iraq Petroleum and Associated Companies. Field observations, measuring and sampling of outcrop sections, and reconnaissance field mapping were later supplemented by photogeological examination and mapping, and a simplified geological map of the island was made. This work, together with observations by H.R. Bichan, (the first one, who concentrated his study principally on the basement rocks of the Socotra archipelago) made as part of an expedition sponsored by the British 241
  • 242. Middle East Command in 1967, are summarized in a report published in 1970. (Beydoun, Z. R. & Bichan, H. R., 1970) 4. On The Forth Stage or The Yemeni Geologists Stage, (1968-Until Today): In the middle of 1975, Siebencs Oil and Gas Ltd. (after known as Dome Petroleum Ltd.) obtained a production- sharing contract area of offshore waters located south and southwest of Socotra. A reconnaissance aeromagnetic survey of the area indicated the presence of at least 2,000 meters of sedimentary rocks above basement. The basement topography was shown to be complex, with series of deep basins separated by high areas. The magnetic survey was immediately followed by a seismic survey and on November 1978, Siebens Samah-1 commenced, reaching a total depth of 2,620 meters. 7.3 GEOLOGY OF SOCOTRA ISLAND Beydoun, Z. R. & Bichan, H. R., 1970 describes a maximum thickness of 300 meters of Lower and Middle Cretaceous limestones, with some basal sandstones, deposited on an igneous and metamorphic basement peneplain, followed without an apparent break by 400 meters of cliff forming shelf limestones of Paleocene and Eocene age. Oligocene-Miocene chalky deposits are preserved only in structural depressions. Siebens geologists report finding Paleozoic Permian (?) limestone and sands below the Cretaceous unconformity in southeastern Socotra. Based on the similarity of the composition of the Cretaceous section, Beydoun supports the hypothesis by Laughton (Laughton, A. S., 1966) and others that pre-rift Socotra was situated along the Arabian coast, close to Oman. He furthers postulates (Beydoun, Z. R., 1970) that the Socotra region may be ‘the eastern prolongation of the North Hadramawt Arch’’. The structure of Socotra is dominated by three main uplifts, oriented in an east-west direction, involving the basement and overlying sediments. North-east-southwest faulting separates these. In the western part of the island, west-northwest-east-southeast block faulting becomes dominant. South of the Socotra continental shelf, and east, off the Somalia coast, lies the deep North Somali basin. In the offshore continental shelf region, Siebens’ seismic work shows a series of narrow uplifts separated by deep troughs, all trending in an east-west direction. The island of Samha and Darsa are situated on another block, Abd al Kuri is on a separate block. South of Samha and Darsa, and separated from them by a highly faulted trough area, an 242
  • 243. east-west-trending uplifted fault block, or horst, occupies the central part of the contract area. Structural movement along a series of north-south faults, accompanied by doming of the sediments, resulted in a series of high and low areas superimposed on the uplift. Siebens mapped three prominent seismic events: • A limestone layer between sequence of claystones believed to be at the top of the Paleocene. • A shale-limestone interface believed to occur at the top of the Cretaceous. • And an event at the base of the Cretaceous section correlating with a thick layer of volcanics at the well location. A basement reflection was also mapped locally. The Siebens seismic interpretation is questionable. Line location was determined by satellite navigation. At this latitude and longitude, satellite passes are infrequent and distant, and precise vessel location cannot always be accurately fixed. Bathymetric data in the area are not precise, and velocity determinations difficult. Serious misties with, intersecting lines were found throughout the area. 7.4 STRATIGRAPHIC SUMMARY OF SAMAH-1A Siebens, Samah-1A was located on the most prominent of the structurally high features on the indicated horst block in a water depth of 115 meters. The well penetrated 938 meters of bedded clays, marls, and marly limestones identified as Eocene and Paleocene in age, and 1.334 meters of interbedded limestones, marls, and dolomites, with sandstone beds near the base, all of Cretaceous age. At the base of the Cretaceous section, 22 meters of volcanic tuff and lava were penetrated. Beneath the Cretaceous, 125 meters of sandstone and dolomitic marl were assigned a Triassic age, and 152 meters of granite wash with thin dolomite stringers were determined to be of Permian age. A total of 46 meters of pink granite, cut by altered basic dike material, were penetrated in the basement. No beds of Oligocene or Miocene age were identified, but it is possible that the uppermost shales in the Eocene section may be of later age. 7.5 OIL AND GAS PREDICTION Patchy minor oil shows were encountered in the lower Cretaceous section between 1,880 and 2,275 meters. Dolomitic beds within the Permian granite wash section had poor to fair porosity and displayed moderate dry gas shows. These shows increased within the basement, and were interpreted as fracture production. Log analysis indicates that the Permian section is gas saturated. 243
  • 244. Sedimentological and geochemical analysis of samples and cores from the Samah well indicate that good reservoir beds are present in the Permo-Trias continental sandstones, in carbonate reef flank and shoal deposits, in secondary dolomites, and in sandstone interbeds, particularly in the lower Cretaceous section. The well contained no thick, continuous sequence of potential source beds, although thin shales between 2,240 and 2,290 meters were determined to be fair to good source rocks for oil. And it is entirely possible that adequate oil sources can be expected to exist in Cretaceous and possibly Jurassic beds in deeper parts of the basin where their maturity can also be anticipated. Other structural feature is present on the horst block where the Samah-1A well was drilled. Reef buildups along the south side of the uplift are suggested by the seismic mapping, and an expand Paleozoic –Triassic section may be present along the flanks of the uplifted area. A large structure is present in the southern part of the area. Its location closer to the margin of the North Somali Basin, together with its size, are positive factors enhancing its favorability for further exploration? In any case, the geology of the Yemeni Island of Socotra with Siebens, Samah-1A well has not just demonstrated that a sedimentary section with considerable petroleum potential is present in the Socotra area, but also put a big question on the presence of Eocene (? Upper Eocene), Triassic (? Middle and Upper Triassic) Fig. (7.1): Socotra Island (Republic of Yemen) 244
  • 245. Fig. (7.2): Socotra Island (Republic of Yemen); 1886. 245
  • 246. CHAPTER 8: OIL AND GAS PROSPECT IN THE YEMENI SECTOR OF RUB AL-KHALI BASIN 242 8.1 INTRODUCTION 243 8.2 THE YEMENI SECTOR OF RUB AL KHALI BASIN GEOLOGICAL RESEARCH HISTORY WORK 244 8.3 THE RUB AL-KHALI SAND DESERT 246 8.4 THE YEMENI SECTOR OF RUB AL-KHALI BASIN 247 8.5. SATELLITE IMAGES INTERPRETATION 247 8.6 NEW LOOK TO THE AREA 248 8.7 CONCLUSION 249 8.8 RECOMMENDATION 249 246
  • 247. CHAPTER 8 OIL AND GAS PROSPECT IN THE YEMENI SECTOR OF THE RUB AL-KHALI BASIN 8.1 INTRODUCTION It is known that one of the world's largest exploration successes of the 1980s was the discovery, by Canadian Occidental and partners, of constellation of oil pools in the Masila region, Sayun Al-Masilla Basin, of Yemen (Fig. (2.3)). The presence of several hundred million barrels of recoverable oil has been proved by drilling within reservoirs ranging in age from Jurassic to Cretaceous, with most reserves in Lower Cretaceous sandstone of the Qishn Formation (Peter E. Putnam, George Kendall, and David A. Winter, 1997). The discovery of commercial oil and gas in several interior Mesozoic rift basins of Yemen in the late of 1980s and in the early 1990s after the Yemeni unification, spurred many oil companies to enter the exploration race and carry out detailed seismic surveys. This led to intensive explorations drilling in many areas (Figs. (2.1A), (2.1B) and (2.2)). The Yemeni sector of the Rub al Khali Basin, (Fig. (2.3)) the main subject of this chapter, is one of those areas, which found some care in the past and attracts many oil companies in the present time. Note (1): This area must took more care, due to: 1. Al-Ghawar oil field one of the world's largest oil fields has been found in the Rub al Khali Basin. 2. Oil, which is exploited in that's area is of excellent quality. 3. Oil Companies, which drilled exploration wells in the Yemeni sector of Rub al Khali basin (in Qinab, Hathout and Shahr area), had penetrated Paleozoic clastic reservoirs with core porosity ranging between 5% and 25%, 120 md to 3,2 d (Darsi) permeability and age from Middle Cambrian to Early Permian (Nani A.S.O., 1998). 4. The Qusayba (lower Silurian) shales, which is the principal source rock for Paleozoic discoveries in Saudi Arabia is present in the above mentioned areas. 5. Much of the southern flank of the basin lies within northeastern Yemen, with the regional Paleozoic Hadramawt Arch forming the southern basin margin onto which all Paleozoic and Early Mesozoic sedimentary sequences pinch out. 247
  • 248. 6. Northward into the basin, the flank slopes gently but in a step-like manner and the sedimentary column thickness increases from about 2 km near the crest of the Hadramawt Arch to over 4 km by the Yemeni-Saudi border (Powers, et al.,1966; Beydoun, et al., 1998). On this Chapter, I am going to introduce my research study work with Professor Wang Xi Kui. That work led to a new look to the area. That’s new look to the area depends on our study to: 1. The geological research history work in the area, 2. The neotectonic and the new crust movement. 3. A collection of satellite images, which had been taken of the Republic of Yemen during the period from 1994 to 1997 (Fig. (8.1; 8.2; … 8.27) ) with hundreds of airophotos and satellite images, taken to different part of the Peoples Republic of China. (As an exemplars to find a case study to the Yemeni Sector of the Rub al Khali Basin). And this led us to introduce a new idea for a new project, which we hope is going to help future petroleum exploration activities and attract foreign exploration investment to work in the Yemeni sector of the Rub al Khali Basin. 8.2 THE YEMENI SECTOR OF RUB AL KHALI BASIN GEOLOGICAL RESEARCH HISTORY WORK According to my new division to the geological research history work of the Republic of Yemen to four stages (Nedham M. Darsi, 2000) It is so clear now, that: 1.On the First Stage (The First Systematic Geological Observation Stage or Carter's Stage), 1852-1901: No kind of geological studies had been detected in the Yemeni sector of Rub al Khali basin. 2. On the Second Stage or the Hinterland Studies Stage, (1902-1946) and the Third Stage (The First Systematic more detailed Stratigraphic and Geological Studies Stage or Beydoun, Z.R.'s Stage, (1947-1967): Geological field investigation, supplemented by photogeologic and ground mapping covering the entire territory, were carried out by the Petroleum Concessions Ltd, one of the Iraq Petroleum Company and associated companies (IPC and Associated companies) between 1937 and 1960. 248
  • 249. 3. On The Third Stage (The First Systematic more detailed Stratigraphic and Geological Studies Stage or Beydoun, Z.R.'s Stage), 1947-1967: Bunker, D.G. wrote about the southwest Borderlands of Rub al Khali, in 1953. From 1961 to early 1967, Pan American International Oil Company through a subsidiary, Pan American Hadhramawt Oil Company (PAHOC) drilled four wells (Hoowarin, Tarfayt and Core Hole 88 reached Precambrian basement and the forth was abandoned in the Cretaceous sediments). 4. The Fourth Stage or The Yemeni Geologists Stage (1968 - until Today): 4.1 It is known that, the Petroleum and Minerals Board (the PMB) was established, in 1970 in former South Yemen. During the period from 1970 to 1973, the joint of former South Yemen-Algerian Petroleum Company (SYAPCO) drilled Taur-1 in 1974 and Taur-2 was commenced. In 1974, a group of experts from Cuba assumed the drilling operation from SYAPCO and with former PMB completed Taur-2, Taur-3 and drilled Thamud-1 and Hathout-1. In September 1976, the functions of the PMB were broadened and the Petroleum Exploration Board (the PED) was created (The Petroleum Exploration and Production Board, Aden Branch, as known now), led different activities on studying the geology of this area. As a result of their work on the Yemeni sector of Rub al Khali basin, wells as Taur-2, Taur-3 and Hathout-1 was drilled. A group of the P.E.D.'s Engineers, Technician and workers, work hard on this area, and their work is highly appreciated. On Mar. 27 1979, B. Kuzin and Mohammed Ba'abad made a Stratigraphic Correlation, for wells drilled in that area correlative with wells located in the adjacent area at that time. Note (2): The Petroleum Exploration and Production Board (P.E.P.B.) is responsible for all petroleum exploration and related activities and is interested with the exploration for oil and gas in the Republic of Yemen on its own, or in association with foreign companies through production sharing agreements. The P.E.P.B. has a professional staff and other administrative personnel. 4.2 Between 1975 and 1979, as a part of its assistance program, TechnoExport, the former Soviet Technical Assistance Organization, had recorded aeromagnetic surveys covering most of former South Yemen and also a gravity survey had been conducted over specific areas of interest. CDP reflection and refraction seismic had been concentrated in the Yemeni sector of Rub al Khali basin and as a result of their work in the area, wells as Hathout-2 Shahr-1 were drilled in 1981-82. 249
  • 250. Note (3): The field investigation had been augmented from time to time by Czechoslovakian and German technical personnel. 4.3 In the Yemeni sector of the Rub Al-Khali basin, first Bahad flower structure was detected from the seismic interpretation and then later Qinab flower structure had detected from the seismic interpretation by Elf Acquitaine Petroleum B.V, during the first phase of exploration in their ex-block 11, in 1989. 4.4 A group of professional staff and other administrative personnel of the Petroleum Exploration and Production Board (P.E.P.B.) made a Geological Review of North Hadhramaut Basin (the Yemeni sector of Rub al Khali basin). (Faisal M.S. Haitham, Mohammed A. Abdellah, Hussain A. Fadel, Nagib S. Thabet, Sulaiman Khamis, Nabeel A. Saeed, Saleh A. Al-Dahi, Tareq Abdulrahman and Abdul Hakim Saroor, 1998). 8.3 THE RUB AL-KHALI SAND DESERT: The Rub al Khali sand desert or the Empty Quarter (as also known) is a huge region of sand covering about c.225, 000-sq. mi. (582,750 sq. km). It is one of the largest sand deserts in the world and the great desert of the Arabian Peninsula. The desert occupies much of the southern interior of the peninsula, from the highlands of the Nejd (to the north) to the plateaus of Hadhramawt (to the south); it slopes from an altitude of 3,300-ft (1,006 m) in the west to near sea level in the east. The sand dunes in the Rub al Khali sand desert rise to over 660 ft (200 m) in the southwest (The Columbia Encyclopedia, 1993). The dunes are mainly distributed in parallel to sub parallel ridges (called uruq), separated by narrow flat stretches of gravel, gypsum, or silt (shuquq). The trend of the southern border of the desert is east-northeast, which is also roughly the trend of the dune ridges. Slip faces of the dunes are generally south, but some north-facing slip faces have been observed. Some migration of dunes takes place; however, the migration seems to be up by seasonal wind directions, so that migration in any specific direction is difficult to detect (World Bank, 1983).There are salt marshes and pans in the southeast. Rub al Khali is connected to the Nafud desert in the north by the Dahna, a narrow corridor, 800 mi. (1,287 km) long southwest. The desert comprises more than 25% of Saudi Arabia. It is extremely dry and virtually uninhabited. Only the southernmost fringe of which reaches into the Republic of Yemen (The Columbia Encyclopedia, 1993). A much smaller area is the Ramlat Sabatayn sand desert. It stretches eastward from the foothills in the north part of the Republic of Yemen and in Bayhan province, where it is some 100 kilometers wide, into the Hadhramawt drainage basin, occupying roughly the western extension of the Wadi Hadhramaut structural trough. The dunes lose both height and lateral extent eastward, until they die out as low isolated 250
  • 251. patches of sand some five kilometers in width near Shibam in Wadi Hadhramaut. The Ramlat Sabatayn area is again one of dune ridges which, however, are less regular than those of the Rub al Khali with a trend roughly east-northeast in the west, are some 50 meters in the height, and are eastward and become irregular toward the east. Migration of the sand is largely offset by seasonal changes in the prevailing winds and by thermal disturbances (World Bank, 1983). 8.4 THE YEMENI SECTOR OF THE RUB AL-KHALI BASIN Several depressions are superimposed on the Arabian Shelf and at one time for another have received thick deposits relative to adjacent parts of the platforms. Such basinal sags have formed in the northeastern Rub al Khali, northern Persian Gulf, Dibdibah, and Sirhan Turayf areas. Seismograph and structural drill work in the Rub al Khali Basin have outlined an elongate basin. Width of the basin is relatively uniform throughout its length, eraging about 300 km (Powers, B. W., Ramirez, L. F., and Redmond, C. D.,1966). It is known that the Yemeni sector of the Rub Al-Khali basin forms the southern flank of this huge structural downwarp, which originated in the early Paleozoic as intracratonic sag later in the Paleozoic (Sykes, R.M. and Abu Risheh, A.K., 1989; Beydoun, 1988, 1989, 1991; Husseini, 1989). This feature is bounded on the north by the sand dunes of the Rub al Khali and on the south by the Ramlat Sabatayn sand desert. Much of the southern flank of the basin lies within northeastern Yemen, with the regional Paleozoic Hadramawt Arch forming the southern basin margin onto which all Paleozoic and Early Mesozoic sedimentary sequences pinch out. Northward into the basin, the flank slopes gently but in a step-like manner and the sedimentary column thickness increases from about 2 km near the crest of the Hadramawt Arch to over 4 km by the Yemeni-Saudi border (Powers, et al.,1966; Beydoun, et al., 1998). 8.5 SATELLITE IMAGES INTERPRETATION According to (Prof. Wang Xi Kui and Me) study on a collection of satellite images, which had been taken to the eastern part of the Republic of Yemen during the period from 1994 to 1997 (Figs (8.1), (8.2), … (8.27) ) and hundereds of airophotos and satellite images, which had been taken to different part of the People’s Republic of China. We concentrated our attention onto the following more important satellite images, (Figs. (8.16) and (8.22)), due to: 1. Those satellite images were related to the Yemeni sector of the Rub Al-Khali basin. 2. The very clear images of different faults types shown on the surface, which we classified them according to their directions and trend, to: First type: Faults with a NE–SW directions (very clear on the satellite images). 251
  • 252. Second type: Faults with E–W and ENE-WSW directions (clear to very clear on the satellite images). Third type: Faults with an N–S and NNE-SSW directions (clear to very clear on the satellite images) Forth type: Faults with a NW–SE directions (clear to a little clear on the satellite images). 3. According to the character of the Satellite images, we found a black material filling these faults on the surface, which looks like natural asphalt (?). Here we want to drew People, who are interested in this field on the following fact: The same example was found in Kelamayi oil field, a famous oil field in the Northwest of the Peoples Republic of China, located to the margin of Zhunger Basin (Jurassic Formation Ð oil and gas bearing layer, oil and gas stored in overthrust structures). This oil field first time discovered by the local villagers, who found that black material on the surface and then known as asphalt. 8.6 NEW LOOK TO THE AREA Based on our study to the geological research history work, the neotectonic movement, the new crust movement, and our interpretation for the satellite images, we have a new look to the area. This new look to the area depending on our new thinking, that during the successive rift phases, (The Karroo Rift Phase; The Somali Rift Phase; The Mascarene Rift Phase; The Yemen Rift Phase), the expected main extensional faults trend and the minor extensional faults trends changed their direction. Especially, during the recent time, where we find that: 1. The first type of faults, which has the NE-SW directions, is a normal and oblique normal fault. 2. The second type of faults, which has the EÐW and ENE-WSW directions, is a divergent sinistral wrench faults and has the same trend of the southern border of the desert, which is also roughly the trend of the dune ridges. 3. The third type of faults, which has the N-S and NNE-SSW directions, is divergent dextral wrench faults. Note (4): The second type of faults and the third type of faults are a share faults type, with right and left hands. 5. The forth type of faults, which has NW-SE directions, is over thrust faults. 8.7 CONCLUSION 1. As a result of our study, we think that a new rift phase started in the area during the recent time. 252
  • 253. 2. On this new rift phase: a. The first type of faults, which has the NE-SW directions, is a normal and oblique normal fault. They are parallel to the direction of the largest principle stress of the Arabian plate. b. The forth type of faults, which has NWÐSE directions, is over thrust faults. Their extensional fault trend resulted by the largest principle stress of the Arabian plate. 3. We think, that this new stage has the same main rift trends like the Karroo rifts phase (?). 4. The natural asphalt (?) shown on the surface of this area by the satellite images might be a very clue for looking for a new petroleum discoveries. 8.8 RECOMMENDATION 1. It is recommended that a very highly qualified team study the Yemeni sector of Rub al Khali basin for recognition of crustal zones of weakness, their trend and origin is thus of vital importance in the interpretation of rift structures. We believe that this area, which took some care in the past and attracts many experts in the present time, is not going just to surprise all with its oil and gas discoveries, but also with its very rich geological data in the future. 2. The most important thing, that we want to drew the Ministry of Oil and Mineral Resources, foreign companies and all who are interested in this area to concentrate their exploration attention on the following two coordinate points and the adjacent area around them: First Point: N 18.46O / E 51.05O Second Point: N 18.22O / E 49.67O 253
  • 254. Fig. (8.1) Satellite Images No.1: Arabian Sea (N19.25-E58.71) Fig. (8.2) Satellite Images No.2: Arabian Sea (N19.15-E58.77) 254
  • 255. Fig. (8.3) Satellite Images No.3: Yemen 14, Sanaw (N18.17-E50.78) Fig. (8.4) Satellite Images No.4: Yemen 15, (N17.51-E51.23) 255
  • 256. Fig. (8.5) Satellite Images No.5: Yemen 16, (N17.38-E51.31) Fig. (8.6) Satellite Images No.6: Yemen 17, (N18.46-E51.05) 256
  • 257. Fig. (8.7) Satellite Images No.7: Yemen 18, Wadi Rakhawt (N17.79-E51.50) Fig. (8.8) Satellite Images No.8: Yemen 19, (N17.69-E51.57) 257
  • 258. Fig. (8.9) Satellite Images No.9: Yemen 20, Desert (N17.69-E50.28) Fig. (8.10) Satellite Images No.10: Yemen 1, Desert (Latitude Longitude at Image center N17.11- 50.67) 258
  • 259. Fig. (8.11) Satellite Images No.11 Yemen 2, Desert (N16.66-E50.96) Fig. (8.12) Satellite Images No.12: Yemen 3, Al Mujaza’ah (N17.28-E49.65) 259
  • 260. Fig. (8.13) Satellite Images No.13: Yemen 4, (N16.36-E50.08) Fig. (8.14) Satellite Images No.14: Yemen 5, (N16.52-E50.16) 260
  • 261. Fig. (8.15) Satellite Images No.15: Border Saudi Arabia-Yemen (N18.57-E49.43) Fig. (8.16) Satellite Images No.16: Yemen 6, (N18.22-E49.67) 261
  • 262. Fig. (8.17) Satellite Images No.17: Yemen 7, (N17.90-E49.89) Fig. (8.18) Satellite Images No.18: Yemen 8, (N17.58-E50.12) 262
  • 263. Fig. (8.19) Satellite Images No.19: Yemen 9, (N17.25-E50.36) Fig. (8.20) Satellite Images No.20: Yemen 10, Jabal Mahrat (N16.93-E50.57) 263
  • 264. Fig. (8.21) Satellite Images No.21: Yemen 11, Jabal Mahrat (N16.77-E50.67) Fig. (8.22) Satellite Images No.22: Border Saudi Arabia-Yemen (N18.64-E51.36) 264
  • 265. Fig. (8.23) Satellite Images No.23: Yemen 12, (N17.97-E51.81) Fig. (8.24) Satellite Images No.24: Yemen 13, (N17.85-E51.88) 265
  • 266. Fig. (8.25) Interpreted satellite Images No.6: Yemen 17, (N18.46-E51.05) 266
  • 267. Fig. (8.26) Satellite Images No.25: show first projected point 267
  • 268. Fig. (8.27) Satellite Images No.26: show second projected point 268
  • 269. CHAPTER 9: THE (3D.Y.G.M. – TIN FOR ALL): THE THREE DIMENSION YEMENI GEOLOGICAL MODEL – TIN FOR ALL 277 269
  • 270. CHAPTER 9 THE (3D.Y.G.M. – TIN FOR ALL): THE THREE DIMENSION YEMENI GEOLOGICAL MODEL – TIN FOR ALL In 1985, I was admitted to the Patrice Lumumba Peoples’ Friendship University decorated with the order of friendship among Peoples and in 1991 completed the full course of the same University having specialized in ‘’Geology and Exploration of Mineral Deposits (Oil and Gas Fields).By the resolution of the state Examination Commission of May 29, 1991, I am qualified as: Petroleum Engineer, Geologist and by the special of the state Examination Commision I am awarded the degree of master of science in geology. During my studing in the Patrice Lumumba Peoples’ Friendship University decorated with the order of friendship among Peoples and especially when I finished my fourth course. I had a new modest idea for a new project on a new portable tin, which can be used in the field of geology. And as a result of my work done on improving this modest project, the above mentioned idea is already regestered in Yemen, in1995. I called the above mentioned Project Tin, The 3DYGM For All Tin.. The Term 3DYGM- For All Tin means (the Three Dimention Yemeni Geological Model For All Tin). This Projected Tin will be used to construct the following kind of models: 1. Geological Wells Sections models 2. Cross Sections models. 3. 3D (three Dimension) geological models. This new Projected Tin, which look like a mathimatical set is going to be used by secondry school students, and by the students of institutes, colages and universities as well as by the researchers and those working in the field of oil. This Projected Tin, which born in Moscow (Russia), grew, improved and registered in Aden (Yemen), published and introduced in brief, as a part of my Ph.D. Thesis, discussed for the first time outside Yemen, here in Changchun (China) is going to find a wild application in the near future. (See attached Figs. (9.1), (9.2), (9.3) and (9.4)) And then, the most interesting results and most important facts, we are going to receive as a result of using the 3DYGN For All Projected Tin in the field of geology is that, most of it users are going to like it and to ask for more and more specific serials of the above mentioned Tin. (For more information, I would like to ask interested reders in this Projected Tin to read the interview held by the 14TH October Newspaper correspondent, (this newspaper is one of the most famous and more public newspapers in Yemen), with me on the 25th of August 1994). 270
  • 271. Fig. (9.1): The 3DYGM-For All Tin; (Outer View) 271
  • 272. Fig. (9.2): The 3DYGM-For All Tin; (Inner View) 272
  • 273. Fig. (9.3): The 3DYGM-For All Tin; (A Column Construction) 273
  • 274. Fig. (9.4): Using the 3DYGM-For All Tin to make a Geological Well Section 274
  • 275. CHAPTER 10: THE (T.G.T.C.): AL-TOHAITA (SER YA KAOS) GEOLOGICAL TIME CLOCK 283 275
  • 276. CHAPTER 10 THE (T.G.T.C.): AL-TOHAITA (SER YA KAOS) GEOLOGICAL TIME CLOCK Suppose that you have a wall clock in your house. This wall clock tell and show you the whole scenario of earth history evolution supported with animated pictures and voices two times per day. The First Hour on this clock introduce the Origin and the Early Evolution of the Earth; the Mountain Building and Drifting Continents, the Deep-Sea Floor and Plate Tectonics, the Pre Paleozoic History as an introduction to understand the Origin of the Continental Crust and the Organic Evolution. (This First Hour show, can be seen from 00:00 a.m. to 01:00 a.m., and from 00:00 p.m. to 01:00 p.m. every day). The remaining hours on this clock show the Earliest, the Middle and the Late Paleozoic History; the Pangea its Makeup and Breakup; the Mesozoic Era; the Cenozoic History, the Pleistocene Glaciation and the Rise of Man and at the end the best of all possible worlds? I believe in, that listening and looking to this kind of clock every where we go, two times per day, is going to make the Evolution of Earth History known by all. This new clock, (My new project), I called it Al-Tohaita Geological Time Clock (T.G.T.C.). (See Figs. (10.1) and (10.2)) * Al-Tohaita (or Ser Ya Koas) is the name of a small Yemeni historical village 10 km (ENE) from the famous Yemeni city, Zabid. I gave its name to the new projected clock to show our same origin. I am shore, that using the above mentioned clock, the Al-Tohaita Geological Time Clock, in the near future is going to make it easy to produce another types of this clock with different functions. 276
  • 277. Fig. (10.1): Al-Tohaita Geological Time Clock (TGTC); (Type No.1) 277
  • 278. Fig. (10.2): Al-Tohaita Geological Time Clock (TGTC); (Type No.2) 278
  • 279. CHAPTER 11: DISCUSSION, CONCLUSION AND RECOMMENDATION 287 11.1 Discussion 288 11.2 Conclusion 289 11.3 Recommendation 290 279
  • 280. CHAPTER 11 DISCUSSION, CONCLUSION AND RECOMMENDATION 11.1 DISCUSSION 1. Based on my new classification and division to the Geological Research History Work of the Republic of Yemen to four stages and my pervious published papers on the Yemen Times Newspaper I can confidently assume, that: • it is easy now to wrote a book about the first and the most famous Geologists, who play a great role in the geological research history work in the Republic of Yemen during the period from 1852 until Today. • it is easy now to teach our student in the university, this bright part of our geological research history work • There are many Peoples, Researchers, and Foreigners, who are interested in this field, who would like to work in Yemen, at the same time they would like to know more about the geological research history work of the Republic of Yemen. • It is so necessary now for every one, who would like to publish a book or a work on the geology of Yemen to mention the Four Stages of the Geological Research History Work in the Republic of Yemen. • This study led to significant improvement in imaging about the geological research history in the Republic of Yemen, particularly about the first and the most famous geologists, who worked visits, worked and this has been key to understanding. • On the whole, it is my belief that it is broad in scope so as to serve both the beginning geology major and the under graduate seeking to learn about or to make him read about the geological research history work in the Republic of Yemen. 2. It is known, that the main aim of my new table for the whole Yemeni Lithostratigraphic Units and Nomenclature is to solve chronic problem related to the Yemeni Lithostratigraphic Units and Nomenclature. I planned to use the same table as a whole or partly to introduce many interested geological issues in the near future. 3. A quick look to my work done on mapping and modelling the whole eastern part of Yemen (from the basemenent to the surfase), show the huge conclusions and recommendation we can resieve from such work. In my opinion, I must continue this work and with one main aim to discover a new promising 280
  • 281. geological structures. This well lead to an increase in the Yemeni production, the reserve and oil prospects as well. 4. Using the two new projected patent methods, the (3D.Y.G.M. – Tin For All): The Three Dimension Yemeni Geological Model - Tin.For All and the (T.G.T.C.): Al-Tohaita (Ser Ya Kaos) Geological Time Clock are going to ease studing and understanding Modelling and the Whole.Evolution of Earth History. 11.2 CONCLUSIONS This Work, lead finally to the following new modest suggestions: 1 A new classification and division to the Geological Research History Work of Yemen.. 2 A new table for the whole Yemeni Lithostratigraphic Units and Nomenclature. 3 A new explanation to the anomaly in the Yemeni Lithostratigraphic Units and Nomenclature, having the same geological time line (the same age), by relating such anomaly to the geological history of the area, especially the anomaly in tectonics. activities and the process of sedimentation. 4. A new subdivision to the Yemeni Paleozoic sediments, into two depositional sequences, i.e. from young to old: b. UPPER PALEOZOIC (Devonian – Permian) / TRIASSIC (Lower Triassic) (?) a. LOWER PALEOZOIC (Cambrian (?) - Lower Silurian (Llandoverian)) 5. A new subdivision to the whole Phanerozoic sedimentary sequence of the Republic of Yemen into five depositional sequences, i.e. from young to old: e. OLIGOCENE / MIOCENE-RECENT d. CRETACEOUS (Lower Hauterivian to Maastrichtian) / PALEOCENE – MIDDLE EOCENE c. JURASSIC – CRETACEOUS (Lower Berriasian to Lower Valanginian) b. UPPER PALEOZOIC (Devonian – Permian) / TRIASSIC (Lower Triassic) (?) a. LOWER PALEOZOIC (Cambrian (?) - Lower Silurian (Llandoverian)) 6. A new lithostratigraphic column suggested for the Whole Yemeni Phanerozoic sequence. 7. A new suggestion, implies that the North Hadhramawt Arch became pronounced during the Lower Paleozoic as a result of uplift in Cambrian (?) - Lower Silurian (Llandoverian) times. 281
  • 282. 8. My personal field notices and records show, that the Yemeni Lithostratigraphic Units characterised by some important factors, such as Lithology changes, Rate of Penetration (increase and decrease), background gas (increase and decrease) and the chromatographic analysis. 9. A new work done on mapping and modelling the whole eastern part of Yemen (from the basemenent to the surfase). The above mentioned conclusions are the result of my work for 8 years in the Petroleum Exploration and Production Board (Aden Branch), Ministry of Oil and Mineral Resources (Yemen) and my research study work on my Ph.D. Thesis in Jilin University (Changchun City, Jilin Province, China). It is clear now, that this work gave, give and well give a new look to the Yemeni geology, It is time to say thank you for allowing me to contact you this past years. I have appreciated hearing from many of you. Your input and suggestions have been very helpful. Hope, it is the first step in right direction. 11.3 RECOMMENDATIONS 1. We in the Republic of Yemen must give a high attention to the Environmental Geosciences. It is known that the global warming issue poses a number of potential challenges and opportunities for the oil industry. Ongoing negotiations are defining not only targets for greenhouse gas reduction but also mechanisms to enable countries and companies to respond. A broad range of options exists to reduce or sequester emissions. So it is recommended to discuss some of the important technical, economic, and political questions that surround the ultimate viability of this option. 2. If we really want The Geological Research History Work in the Republic of Yemen to be easy to read and to understand. We must make a restudy on the history of the Exploration Activities, a restudy on the history of Companies 's Work and a restudy on the history of Scientific Expedition Work in the Republic of Yemen. And. This entire things in accordance to my classification and division to the Geological Research History Work in the Republic of Yemen to four stages. 3. It is recommended that a very highly qualified team study the Yemeni sector of Rub al Khali basin and the Yemeni Island of Soqatra. 4. Presence of gypsum on the surface of the Yemeni sector of Rub al Khali basin, give us the right to recommend for a new study on the presence of Uranium in the above mentioned area. 282
  • 283. 5. Looking to the future and with a long-term vision in mind, I am deeply confident of the great efforts needed to inter the Fifth Stage or (the Yemeni Geologists Golden Stage) as I hope. In that respect I would like to mention two of the steps that we must do: (A) We in Yemen are highly in need to rebuild the National Crew or Team, who is already ready to solve any problem related to any branch of earth science. (B) We in Yemen also are highly in need to make a restudy on the entire most famous Yemenis Geologists Job. First, to encourage the local work. Second, to connect the theoretical part with the practical part and by the way to answer the most interesting question, which I am shore every Yemeni geologist ask himself always, who is the suitable person, whom we can call the father of Geology in Yemen? 6. I believe in that Yemeni Geology, which took some care in the past and attracts many experts in the present time, is not going just to surprise all with its oil and gas discoveries, but also with its rich and useful data in the near future. 7. Interested people in Yemeni geology must contact the Petroleum Exploration and Production Board (P.E.P.B.). It is responsible for all petroleum exploration and related activities and is interested with the exploration for oil and gas in the Republic of Yemen on its own, or in association with foreign companies through production sharing agreements. 283
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