Sedimentological characteristics of Ajali sandstone at Okigwe, Anambra basin,...Premier Publishers
The Ajali sandstones exposed along Enugu-Port Harcourt Express Road at Okigwe, Imo State, Nigeria were studied to evaluate textural parameters, mineralogy, and statistical measures to depict the depositional pattern of sediments. A total of eleven samples were collected for this study from five locations based on their stratigraphic position (i.e. from top to bottom). Results of grain size analysis reveal a unimodal frequency distribution which indicates a single provenance for the sandstones. Statistics reveals a graphic mean range from 1.5 to 2.8, sorting range from 0.45 to 1.58, skewness range from -0.58 to 0.32, and kurtosis between 0.38 and 2. The sandstones are false bedded and burrowed, medium to fine grained, poorly to moderately sorted, strongly coarsely skewed and platykurtic. The sandstones generally lack of microfauna and macrofossils. Mineralogically, the sandstones contain, on the average, 32.56% monocrystalline quartz, 9.33% polycrystalline quartz, 16.09% plagioclase, 25.91% potassium feldspar, 4.88% clay matrix and 14.27% opaque. The major framework composition classifies the sandstones as sub-feldspathicarenite. Bivariate and multivariate results reveal shallow the Ajali sandstones may have been deposited at fluvial deltaic to marine environments
Petrological Characterisitics and Paleodepositional Environment of the Sandst...iosrjce
Petrological characteristics of sandstones outcropping in Bende and Isimkpu areas was carried out
using sieve analysis and pebble morphometric studies in determination of the paleodepositional environment for
Sandstone facies of the Ameki Group. Lithostratigraphic studies show that the area is underlain by sandstones,
calcareous sandstone, shales, mudstones and clays. This has been organized into: Unit A: Idima junction shale;
B: Bende sandstone; C: Onuinyang calcareous siltstone and D: Isimkpu sandstone, from oldest to youngest.
Representative sandstone samples were collected from outcrops widely distributed in the area. Results show that
the sandstones are fine to coarse grained and the pebbles are rounded to sub-rounded and dominantly bladed to
elongate. Computed percentages indicate the sandstones are dominantly well sorted, negatively skewed and
extremely leptokurtic. Mean values for the flatness index, elongation and oblate-prolate index (OPI) are 0.47,
0.70 and 2.37 respectively. The synthesis and integration of these values indicated fluviatile with subordinate
littoral/shallow marine setting for sandstones of Ameki Formation in the study area.
Sedimentological and Palynological Approach for Determining the Depositional ...Md. Yousuf Gazi
Sitakund anticlinal structure exposes about 1.5 km of Surma group sediments and has been chosen for a comprehensive study of the
mudrocks depositional environment based on sedimentological and palynological evidences. Five mudrock facies have been identified in
this region. They are Mudstone Dominated, Sand/Silt Streaked Shale, Fissile Shale, Laminated Shale and Lenticular Bedded Shale. The
palynological assemblages from these samples have been analyzed qualitatively, and a variety of pollen, spores, algae and fungi identified.
The pollen and spores have been attributed to parent plants located at the immediate and more regional surrounding areas during the
deposition of these sediments. Palynological assemblages incorporates ample of Palmae grains such as spores in the Palmipollenites and
Proxaperites and predominance of pteridophytic spores. The occurrences and abundances of these pollens indicate that the deposition of the
Surma mudrocks took place at the proximity of the shore level. Coastal fluvial environment is also triumphed after the previous depositional
event which is apparent by the occurrence of palynomorphs of pteridophytes, angiosperms and algal origin.
Sedimentological characteristics of Ajali sandstone at Okigwe, Anambra basin,...Premier Publishers
The Ajali sandstones exposed along Enugu-Port Harcourt Express Road at Okigwe, Imo State, Nigeria were studied to evaluate textural parameters, mineralogy, and statistical measures to depict the depositional pattern of sediments. A total of eleven samples were collected for this study from five locations based on their stratigraphic position (i.e. from top to bottom). Results of grain size analysis reveal a unimodal frequency distribution which indicates a single provenance for the sandstones. Statistics reveals a graphic mean range from 1.5 to 2.8, sorting range from 0.45 to 1.58, skewness range from -0.58 to 0.32, and kurtosis between 0.38 and 2. The sandstones are false bedded and burrowed, medium to fine grained, poorly to moderately sorted, strongly coarsely skewed and platykurtic. The sandstones generally lack of microfauna and macrofossils. Mineralogically, the sandstones contain, on the average, 32.56% monocrystalline quartz, 9.33% polycrystalline quartz, 16.09% plagioclase, 25.91% potassium feldspar, 4.88% clay matrix and 14.27% opaque. The major framework composition classifies the sandstones as sub-feldspathicarenite. Bivariate and multivariate results reveal shallow the Ajali sandstones may have been deposited at fluvial deltaic to marine environments
Petrological Characterisitics and Paleodepositional Environment of the Sandst...iosrjce
Petrological characteristics of sandstones outcropping in Bende and Isimkpu areas was carried out
using sieve analysis and pebble morphometric studies in determination of the paleodepositional environment for
Sandstone facies of the Ameki Group. Lithostratigraphic studies show that the area is underlain by sandstones,
calcareous sandstone, shales, mudstones and clays. This has been organized into: Unit A: Idima junction shale;
B: Bende sandstone; C: Onuinyang calcareous siltstone and D: Isimkpu sandstone, from oldest to youngest.
Representative sandstone samples were collected from outcrops widely distributed in the area. Results show that
the sandstones are fine to coarse grained and the pebbles are rounded to sub-rounded and dominantly bladed to
elongate. Computed percentages indicate the sandstones are dominantly well sorted, negatively skewed and
extremely leptokurtic. Mean values for the flatness index, elongation and oblate-prolate index (OPI) are 0.47,
0.70 and 2.37 respectively. The synthesis and integration of these values indicated fluviatile with subordinate
littoral/shallow marine setting for sandstones of Ameki Formation in the study area.
Sedimentological and Palynological Approach for Determining the Depositional ...Md. Yousuf Gazi
Sitakund anticlinal structure exposes about 1.5 km of Surma group sediments and has been chosen for a comprehensive study of the
mudrocks depositional environment based on sedimentological and palynological evidences. Five mudrock facies have been identified in
this region. They are Mudstone Dominated, Sand/Silt Streaked Shale, Fissile Shale, Laminated Shale and Lenticular Bedded Shale. The
palynological assemblages from these samples have been analyzed qualitatively, and a variety of pollen, spores, algae and fungi identified.
The pollen and spores have been attributed to parent plants located at the immediate and more regional surrounding areas during the
deposition of these sediments. Palynological assemblages incorporates ample of Palmae grains such as spores in the Palmipollenites and
Proxaperites and predominance of pteridophytic spores. The occurrences and abundances of these pollens indicate that the deposition of the
Surma mudrocks took place at the proximity of the shore level. Coastal fluvial environment is also triumphed after the previous depositional
event which is apparent by the occurrence of palynomorphs of pteridophytes, angiosperms and algal origin.
The International Journal of Engineering and Science (The IJES)theijes
The International Journal of Engineering & Science is aimed at providing a platform for researchers, engineers, scientists, or educators to publish their original research results, to exchange new ideas, to disseminate information in innovative designs, engineering experiences and technological skills. It is also the Journal's objective to promote engineering and technology education. All papers submitted to the Journal will be blind peer-reviewed. Only original articles will be published.
The papers for publication in The International Journal of Engineering& Science are selected through rigorous peer reviews to ensure originality, timeliness, relevance, and readability.
The Wadi Sikait Complex:
A Fertile- Post-Collisionl Granite-Pegmatite Suite, Eastern Desert, Egypt.
The Pan-African, Wadi Sikait Complex (WSC), in the south Eastern Desert of Egypt, is a late-tectonic, subsolvus strongly peraluminous, S-type, post-collisionl granite in the Sikait area that features an unambiguous genetic linkage with a proximal, zoned cluster of Be-, REE- and Nb-Ta bearing pegmatites (Abu Rusheid and Nugrus-Sikait area). The WSC is an arcuate belt of orthogneisses, migmatites and other high-grade metamorphic rocks, which mark the boundary between the central Eastern and the south Eastern Deserts of Egypt. The WSC consists of seven internal units (WSC-1 to -3 and PL-1 to -4) that range from chemically primitive biotite, garnet and sillimanite granites (WSC-1 and –2) to a highly evolved, tourmaline- and muscovite- bearing pegmatite granite facies (PL-1 to –4) locally containing endogenous emerald/beryl, molybdinite and cassiterite. Salient petrochemical attributes include A/CNK molar which varies from 1.15 to 1.75, a wide range of SiO2 (68.7-76.9%), high Al2O3 (14.1-16.0%), low CaO (<2.35%) and FeOt+MgO+TiO2 (0.36-6.62%), and with increasing fractionation, enrichment of Na2O, K2O, B, F, Be, Rb, Ga and Li, and depletion of Ba, Sr, Zr, REE and LREE. Strong fractionation is also revealed by Al/Ga (1370-6789), Ba/Rb (<0.01-12), Ca/Sr (21-201), K/Ba (19-9545), Mg/Li (4.26-1421), Na2O/K2O (0.21-34), (Ce/Yb)CN (0.89-83.25), and Eu/Eu* (<0.05-2.29). REE distribution patterns of rare-element pegmatites are lower in REE contents and flatter with prominent negative Eu anomaly than those of the related granites. The REE concentration and the (Ce/Yb)CN ratio decrease from the WSC-1 and -2 through PL-1 and -2 (fine-grained leucogranite) and PL-3 (pegmatitic leucogranite) to the PL-4 (potassic pegmatites).
Genesis of the strongly peraluminous, S-type granite and the associated rare-element pegmatite in the Sikait-Nugrus area is explained by a complex interplay of petrogenetic processes. Rare-elements and boron were previously concentrated in (wackes and mudstone) pelitic sediments deposited in large basins. These rocks underwent step-wise rock dehydration reactions involving muscovite and biotite, under fluid-absent conditions, and successively released these elements to anatectic melt. Rare-elements and volatiles were progressively concentrated via crystal-melt fractionation, the Harker trends of which were obscured by two stages of extraction of residual melt and by episodic, subsolidus redistribution via base-cation leaching. The late magmatic history of the WSC is marked by widespread exsolution of a volatile-rich phase, dispersion of a rare-element- F-B-Be-rich fluid along shear zones and ensuing emigration of rare-element-rich melt-fluid systems upward from the cupola, which led to the regionally zoned Sikait-Nugrus area
Petrography, Geochemistry and Age of Volcanic Rocks in the Gurasada Area, Nor...Ikramullah Sultana
This paper proves for the first time the existence of a complex distribution of volcanic rock types occurring in the Gurasada region. At the base of these a bentonite deposit crops out in the Gurasada open pit, followed by pyroclastic deposits represented by pyroclastic breccia and rare tuff levels the youngest rocks are lava flows exposed in the Runcşor Hill. Thermometamorphic products represented by hornfels are described here for the first time within the outcrop area of the pyroclastic breccia. The site observations, petrographic, XRD, RAMAN spectroscopy and chemical analyses indicated the formation of the bentonite deposit by weathering of a vitroclastic tuff, probably of dacitic composition, belonging to a first (more felsic) eruptive stage consisting of Plinian-type explosive volcanism. The pyroclastic breccia, tuffs and lava flows are mainly of calc-alkaline andesitic composition and belong to a second stage of volcanism, which developed intermittently, over a longer period of time. Radiometric dating (K/Ar method) of the rocks indicates the formation of the volcanic-volcaniclastic deposits within a period of 69 to 80 million years ago. These ages confirm that these volcanics belong to the laramic cycle as inferred previously place them at the level of Upper Cretaceous (Senonian).
Sedimentology of the Turonian Ezeaku Sandstone in the Afikpo Basin, NigeriaPremier Publishers
Sedimentological studies, including outcrop logging, facies analysis and paleo-environmental studies were carried out in the Ezeaku Formation outcropping in Akpoha, Ibii, and Amasiri in order to determine the original depositional environment of these sandstone and associated concretions. The sandstone occurs as ridges; four facies were observed: which include bioturbated mudstone with randomly spherical concretions; ripple laminated, heterolithic, interbedded sandstone and mudstone; planar and trough cross-bedded facies; and swaley cross-stratified facies. Such a facies suite indicates that these bars and concretions were formed under a storm-influenced shelfal to shoreface environment. The paleo-current evidenced by the cross-bedding clearly shows a NE-SW paleo-flow indicating the Abakiliki and Oban massifs as provenance sources.
Geological and Geochemical Characterization of the Neoproterozoic Derudieb Me...Premier Publishers
The meta- volcano - sedimentary sequences in the northern part of the Red Sea Hills comprise a sequence of metamorphosed rocks at low green schist facies of metamorphism consisting of lava flows, tuffs to breccias and agglomerates range in composition from basalts and andesites to rhyolites. Geologically the meta volcano sedimentary sequences is divided into metavolcanic rocks and metasediments. The metavolcanic rocks range in composition from mafic to felsic. The metasediments are represented by banded schist, quartzite and marble. The samples collected for study lie within the field of sub-alkaline rocks except one mafic volcanic sample, which plot near the boundary in the alkaline field and thus follow a transitional tholeiitic to calc-alkaline trend (increasing FeO* relative to MgO). The behavior of the large ion lithophile element (LILE) in the studied metavolcanics confirms the early fractionation of plagioclase. These rocks display negative Nb anomalies, suggesting that the melt source was modified by subduction-related fluids. Tectonically all felsic samples fall in the field of volcanic arc granitoids whereas the mafic units plot firmly within the plate margin field.
Exploration in Deep Weathering Profiles, Supergene, R-mode factor analysis; Multi-element association geochemistry; Assessment of Au-Zn potentiality in Gossan; Rodruin-Egypt
Grossular bearing jadeite omphacite rock in the myanmar jadeite areaYMCA Mandalay
The Myanmar jadeitite deposits near Hpakant have attracted remarkable attention of geologists and gemologists not only for being the largest jadeite jade deposit in the world, producing high quality jade with the glassy imperial green for more then 300 years.
The International Journal of Engineering and Science (The IJES)theijes
The International Journal of Engineering & Science is aimed at providing a platform for researchers, engineers, scientists, or educators to publish their original research results, to exchange new ideas, to disseminate information in innovative designs, engineering experiences and technological skills. It is also the Journal's objective to promote engineering and technology education. All papers submitted to the Journal will be blind peer-reviewed. Only original articles will be published.
The papers for publication in The International Journal of Engineering& Science are selected through rigorous peer reviews to ensure originality, timeliness, relevance, and readability.
The Wadi Sikait Complex:
A Fertile- Post-Collisionl Granite-Pegmatite Suite, Eastern Desert, Egypt.
The Pan-African, Wadi Sikait Complex (WSC), in the south Eastern Desert of Egypt, is a late-tectonic, subsolvus strongly peraluminous, S-type, post-collisionl granite in the Sikait area that features an unambiguous genetic linkage with a proximal, zoned cluster of Be-, REE- and Nb-Ta bearing pegmatites (Abu Rusheid and Nugrus-Sikait area). The WSC is an arcuate belt of orthogneisses, migmatites and other high-grade metamorphic rocks, which mark the boundary between the central Eastern and the south Eastern Deserts of Egypt. The WSC consists of seven internal units (WSC-1 to -3 and PL-1 to -4) that range from chemically primitive biotite, garnet and sillimanite granites (WSC-1 and –2) to a highly evolved, tourmaline- and muscovite- bearing pegmatite granite facies (PL-1 to –4) locally containing endogenous emerald/beryl, molybdinite and cassiterite. Salient petrochemical attributes include A/CNK molar which varies from 1.15 to 1.75, a wide range of SiO2 (68.7-76.9%), high Al2O3 (14.1-16.0%), low CaO (<2.35%) and FeOt+MgO+TiO2 (0.36-6.62%), and with increasing fractionation, enrichment of Na2O, K2O, B, F, Be, Rb, Ga and Li, and depletion of Ba, Sr, Zr, REE and LREE. Strong fractionation is also revealed by Al/Ga (1370-6789), Ba/Rb (<0.01-12), Ca/Sr (21-201), K/Ba (19-9545), Mg/Li (4.26-1421), Na2O/K2O (0.21-34), (Ce/Yb)CN (0.89-83.25), and Eu/Eu* (<0.05-2.29). REE distribution patterns of rare-element pegmatites are lower in REE contents and flatter with prominent negative Eu anomaly than those of the related granites. The REE concentration and the (Ce/Yb)CN ratio decrease from the WSC-1 and -2 through PL-1 and -2 (fine-grained leucogranite) and PL-3 (pegmatitic leucogranite) to the PL-4 (potassic pegmatites).
Genesis of the strongly peraluminous, S-type granite and the associated rare-element pegmatite in the Sikait-Nugrus area is explained by a complex interplay of petrogenetic processes. Rare-elements and boron were previously concentrated in (wackes and mudstone) pelitic sediments deposited in large basins. These rocks underwent step-wise rock dehydration reactions involving muscovite and biotite, under fluid-absent conditions, and successively released these elements to anatectic melt. Rare-elements and volatiles were progressively concentrated via crystal-melt fractionation, the Harker trends of which were obscured by two stages of extraction of residual melt and by episodic, subsolidus redistribution via base-cation leaching. The late magmatic history of the WSC is marked by widespread exsolution of a volatile-rich phase, dispersion of a rare-element- F-B-Be-rich fluid along shear zones and ensuing emigration of rare-element-rich melt-fluid systems upward from the cupola, which led to the regionally zoned Sikait-Nugrus area
Petrography, Geochemistry and Age of Volcanic Rocks in the Gurasada Area, Nor...Ikramullah Sultana
This paper proves for the first time the existence of a complex distribution of volcanic rock types occurring in the Gurasada region. At the base of these a bentonite deposit crops out in the Gurasada open pit, followed by pyroclastic deposits represented by pyroclastic breccia and rare tuff levels the youngest rocks are lava flows exposed in the Runcşor Hill. Thermometamorphic products represented by hornfels are described here for the first time within the outcrop area of the pyroclastic breccia. The site observations, petrographic, XRD, RAMAN spectroscopy and chemical analyses indicated the formation of the bentonite deposit by weathering of a vitroclastic tuff, probably of dacitic composition, belonging to a first (more felsic) eruptive stage consisting of Plinian-type explosive volcanism. The pyroclastic breccia, tuffs and lava flows are mainly of calc-alkaline andesitic composition and belong to a second stage of volcanism, which developed intermittently, over a longer period of time. Radiometric dating (K/Ar method) of the rocks indicates the formation of the volcanic-volcaniclastic deposits within a period of 69 to 80 million years ago. These ages confirm that these volcanics belong to the laramic cycle as inferred previously place them at the level of Upper Cretaceous (Senonian).
Sedimentology of the Turonian Ezeaku Sandstone in the Afikpo Basin, NigeriaPremier Publishers
Sedimentological studies, including outcrop logging, facies analysis and paleo-environmental studies were carried out in the Ezeaku Formation outcropping in Akpoha, Ibii, and Amasiri in order to determine the original depositional environment of these sandstone and associated concretions. The sandstone occurs as ridges; four facies were observed: which include bioturbated mudstone with randomly spherical concretions; ripple laminated, heterolithic, interbedded sandstone and mudstone; planar and trough cross-bedded facies; and swaley cross-stratified facies. Such a facies suite indicates that these bars and concretions were formed under a storm-influenced shelfal to shoreface environment. The paleo-current evidenced by the cross-bedding clearly shows a NE-SW paleo-flow indicating the Abakiliki and Oban massifs as provenance sources.
Geological and Geochemical Characterization of the Neoproterozoic Derudieb Me...Premier Publishers
The meta- volcano - sedimentary sequences in the northern part of the Red Sea Hills comprise a sequence of metamorphosed rocks at low green schist facies of metamorphism consisting of lava flows, tuffs to breccias and agglomerates range in composition from basalts and andesites to rhyolites. Geologically the meta volcano sedimentary sequences is divided into metavolcanic rocks and metasediments. The metavolcanic rocks range in composition from mafic to felsic. The metasediments are represented by banded schist, quartzite and marble. The samples collected for study lie within the field of sub-alkaline rocks except one mafic volcanic sample, which plot near the boundary in the alkaline field and thus follow a transitional tholeiitic to calc-alkaline trend (increasing FeO* relative to MgO). The behavior of the large ion lithophile element (LILE) in the studied metavolcanics confirms the early fractionation of plagioclase. These rocks display negative Nb anomalies, suggesting that the melt source was modified by subduction-related fluids. Tectonically all felsic samples fall in the field of volcanic arc granitoids whereas the mafic units plot firmly within the plate margin field.
Exploration in Deep Weathering Profiles, Supergene, R-mode factor analysis; Multi-element association geochemistry; Assessment of Au-Zn potentiality in Gossan; Rodruin-Egypt
Grossular bearing jadeite omphacite rock in the myanmar jadeite areaYMCA Mandalay
The Myanmar jadeitite deposits near Hpakant have attracted remarkable attention of geologists and gemologists not only for being the largest jadeite jade deposit in the world, producing high quality jade with the glassy imperial green for more then 300 years.
Sedimentology and Geochemical Evaluation of Campano-Maastrichtian Sediments, ...Premier Publishers
The Cretaceous sediments in the Anambra Basin (SE Nigeria) consist of a cyclic succession of coals, carbonaceous shales, silty shales, siltstones and sandstones interpreted as deltaic deposits. Statistics reveals a graphic mean range from 1.5 to 2.8, sorting range from 0.45 to 1.58, skewness range from -0.58 to 0.32 and kurtosis between 0.38 and 2 for the Ajali Sandstone. From these results, the sandstones in the area are dominated by medium to coarse grains, poorly to moderately sorted, coarse skewed and very platykurtic sediments. Further sedimentological evaluation in six localities indicates fluvial-flood plain-marginally marine facies for the Mamu and Nsukka Formations and marine for the Nkporo and Enugu Shales. The geochemical evaluations show that total organic carbon (TOC) (8.95wt%) of the samples constitutes that of good to excellent source rock with oil, oil/gas, gas prones for kerogen types I, II/III, III indicated by Rock-Eval S2/S3 (9.13). The high oxygen index (OI) (42.61 mgCO2g-1TOC) suggest deposition in a shallow marine environment. The Tmax (430oC), indicate the immaturity to onset of maturity of these source rocks. Potential reservoir units occur in the fluvial sandstones of the Ajali Formation and in the marginal marine and flood plain sandstones of the Mamu Formation. The shales and claystones of the Nsukka and Imo Formations may provide regional seals.
The International Journal of Engineering and Science (The IJES)theijes
The International Journal of Engineering & Science is aimed at providing a platform for researchers, engineers, scientists, or educators to publish their original research results, to exchange new ideas, to disseminate information in innovative designs, engineering experiences and technological skills. It is also the Journal's objective to promote engineering and technology education. All papers submitted to the Journal will be blind peer-reviewed. Only original articles will be published.
The papers for publication in The International Journal of Engineering& Science are selected through rigorous peer reviews to ensure originality, timeliness, relevance, and readability.
The International Journal of Engineering and Science (The IJES)theijes
The International Journal of Engineering & Science is aimed at providing a platform for researchers, engineers, scientists, or educators to publish their original research results, to exchange new ideas, to disseminate information in innovative designs, engineering experiences and technological skills. It is also the Journal's objective to promote engineering and technology education. All papers submitted to the Journal will be blind peer-reviewed. Only original articles will be published.
Evidence of Clay Mineralization on Tropical Sediments from Afikpo Graben, SE ...Premier Publishers
Sedimentation in the Afikpo graben (SE Nigeria) thus commenced with the Campano-Maastrichtian marine and paralic shales of the Enugu and Nkporo Formations, overlain by the Mamu Formation. The fluviodeltaic and subtidal sandstones of the Ajali Formation lie on the Mamu Formation. The overlying deltaic Nsukka and marine shales of the Imo and Ameke Formations were deposited during the Paleocene. These two formations (Mamu and Nsukka) consist of a cyclic succession of coals, carbonaceous shales, silty shales and siltstones interpreted as deltaic deposits. The primary minerals are Feldspar, Quartz, Pyroxenes, Haematite. The secondary minerals are further classified into two major groups of 1:1 clay minerals and 2:1 clay minerals. The 1:1 clay minerals are kaolinite and halloysite, while the examples of 2:1 mineral are montmorillonite, vermiculite and illite. Clay fractions of shale samples obtained from the Cretaceous Mamu and Nsukka Formations in the Afikpo graben, South eastern Nigeria through the process of sedimentation technique were air – dried and analyzed using the empyrean diffractometer manufactured by Panalytical to determine the presence of clay mineralization in the area. The result shows that the bulk mineral composition of the shales comprises of quartz, clay minerals, carbonates and iron rich minerals, while the dominant clay mineral is kaolinite (70 – 80%) with minor amounts of illite (4 – 7 %) and smectite (10 – 20) as typical composition of tropical sediment.
Base Metal Mineralization in the Precambrian Rocks of Okemesi-Ijero Area, So...Scientific Review SR
The evaluation of base metals in the bedrocks of Okemesi / Ijero area, southwestern Nigeria has
been carried out to assess their potentials, level of accumulation and enrichment. The methodology included
systematic geological and geochemical mapping of the rocks using grid-controlled sampling method at a
sampling density of one sample per 500m. Ten rock samples were collected at different locations of the study
area. The results obtained showed that the major oxides such as SiO
2, Al2O3, TiO
2,
Fe
2O3, MnO, MgO, CaO,
Na2O, K2
O and P2O5 were detected in variable proportions. While SiO2 varied between 70.59% and 98.70%,
Al2O3 ranged between 15.73% and 0.61%. There is abundance of barium (Ba), silver (Ag) and gold (Au) with
concentration values of 1.6-9.8, 1.24-7.1 and 0.05-10.00 ppm respectively. Base metals such as Cu, Zn, Pb, Bi
and Cr enrichment factors and their geo-accumulation index indicates moderately significance to very high
enrichment of Cu (10 – 70%) , Pb (20 – 40%) and Bi (10 – 40%). The geo-accumulation indices suggest
geogenic concentration of the base metals in the host rocks rather than anthropogenic inputs. The PCA elements
loaded Au, As, Ag, Pt and Os on the same factor and they are pathfinder elements of Gold. Correlation
coefficients indicate strong positive correlations between the elements. This implies that they are strongly related
and therefore of the same source, also suggesting geogenic sources.
Lithofacies Analysis and Petroleum Potentials of Parts of Ikom-Mamfe Embaymen...Premier Publishers
An integrated study involving detailed lithofacies analysis and source rock evaluation were carried out to reconstruct the paleoenvironment and assess the petroleum potentials of the Ikom–Mamfe embayment, southeastern Nigeria. Sedimentological field mapping involving detailed description of lithologic characteristics and facies characterisation was carried out. Geochemical studies were carried out to determine the quantity of organic matter total organic carbon (TOC), soluble organic matter (SOM), the organic matter quality (organic matter type) and level of maturity. Results show that the dominant vertical succession of the various lithofacies indicate a general finning upward succession with basal massive pebbly sandstone, medium to coarse grained sandstones with intercalation of shale and mudstones. Seven lithofacies A to G, were identified. These include: conglomerates, massive pebbly sandstone, trough cross-bedded sandstone, planar cross-bedded sandstone, shale/mudstone facies. These facies were compared with established standard facies association for determining paleoenvironment of deposition. The facies analysis carried out pointed to fluvial (alluvial – braided) depositional system as the environment of deposition. TOC values range from 0.05 – 4.13 wt% indicating poor to excellent and SOM range from 200 – 6000 ppm indicating also poor to excellent. The amount of pyrolizable carbon derived as S1 and S2 peaks suggested that the source rocks possess organic matter capable of generating hydrocarbons. Hydrogen and oxygen indices (HI and OI) ranged from 0.24 to 656 and 0.53 to 61.90 mg/gTOC respectively. Analyses of the evaluated source rock shows that the hydrocarbon potential of the study area is lean and typically of a reworked terrestrial deposit of fluvial depositional system.
Lithofacies and palaeoenvironmental reconstruction new microsoft office word ...DrRalimonglaYaden
In the present investigation, an attempt has been made to elucidate the sedimentary facies and depositional environment of tertiary succession of Changki valley comprising of Barail Group, Changki Formation and Tipam Sandstone Formation.
Granomeric Analysis of Mamu Formation and Enugu Shale around Ozalla and Its E...iosrjce
The study area lies within the Anambra Basin which geologically made up of Enugu Shale and
Mamu Formation. This study aimed at determining the geology and depositional environments of these
Formations through field relationship and grain size distribution as well as morphometric studies. The field
data shows Enugu Shale as fissile, light grey with extraformational clast which graded into Mamu Formation
which is made up of alternating sequence of shale, siltstone, mudstone, coal and sand, it shows a fluctuating
environment. The granulometric study of sand member of Mamu Formation shows characteristic very well
sorted, fine to medium grains which were deposited in relatively turbulent well aerated marine environment
probably above wave base. The bivariate and the multivariate results reveal Aeolian/shallow marine deposit.
The fissility of Enugu Shale suggests that it was deposited in low energy environment, distal to proximal lagoon
environment and the presence of extraformatonal clast indicates fluvial incursion. However, it can be concluded
that Mamu Formation was deposited in fluctuating environment ranging from an oxygenated shallow marine to
acidic swampy environment. Hence is paralic Formation.
The name ophiolite derived from Greek root which means
Ophio : snake or serpent Litho : Stone
The green colour, structure and texture of sheared ultramafic rocks is similar to some serpents
Economically :
Massive Sulphide
It founded within pillow lava most of massive Sulphide associated in ophiolites have well developed Gossans (bright colored iron oxide, hydroxides, and sulfides) which is very rich in gold.
Chromite
Stratiform (be tabular or pencil shape) or podiform (irregular shape) within ultra-mafic rocks
These deposits are developed on serpentinite peridotite
Laterites (nickel and iron)
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Keys to paleoenvironmental interpretation of the nkporo formation, afikpo sub basin, nigeria
1. Journal of Environment and Earth Science www.iiste.org
ISSN 2224-3216 (Paper) ISSN 2225-0948 (Online)
Vol 2, No.6, 2012
Lithofacies and Pebble Morphogenesis: Keys to Paleoenvironmental
Interpretation of the Nkporo Formation, Afikpo Sub-Basin, Nigeria
Okoro Anthony. U*, Onuigbo Evangeline N., Akpunonu Eliseus O and Obiadi Ignatius I.
Department of Geological Sciences, Nnamdi Azikiwe University, P. M, B. 5025, Awka. Nigeria.
*anthonyuokoro@yahoo.com
Abstract
The Nkporo Formation in the Afikpo Subbasin, Nigeria, is dominantly shaly but contains two sandstone members
within it. These sandstones host vein quartz pebble beds and dispersed clasts which have been used for pebble
morphometric analysis. As independent functions and dependent variables, pebble morphometric indices of
Coefficient of Flatness, Elongation Ratio, Maximum Projection Sphericity, Oblate-Prolate Index, Roundness and
Form suggest deposition of the sandstones in fluvio-deltaic to littoral settings. Lithofacies analysis identified six
lithofacies, grouped into estuarine delta and marine offshore lithofacies associations. These include trough cross-
bedded sandstone, ophiomorpha burrowed, wave/rippled and planar cross-bedded lithofacies, Inclined heterolithic
lithofacies, fine grained, silty sandstone, lignite/coals, shales/mudstone, interbedded with limestones and oolitic
ironstones lithofacies. The estuarine lithofacies association shows a tripartite subdivision into meandering estuarine
and tidal point bars overlain by estuary funnel tidal creek sandstones, carbonaceous beds; and estuary mouth tidal
and barriers bars and shallow marine shales in a drowned incised valley. The fining upwards lithofacies pattern
suggests deepening and transgression of the sea in a tidal estuarine setting.
Keywords: Lithofacies, Lithofacies association, Pebble morphogenesis, Paleoenvironments, Tidal estuary
1. Introduction
The Afikpo Sub-basin in southeastern Nigeria was installed after the Santonian to early Campanian thermo- tectonic
event which folded and uplifted the Albian – Coniacian sediments of the Benue Trough into the Abakaliki
Anticlinorium/Afikpo Synclinorium. The Nkporo Formation (Campanian – Maastrichtian) is the basal
lithostratigraphic unit of the Afikpo Sub-basin (Figure 1) and comprises dominantly of dark grey to black shales,
sandstone, minor limestone and oolitic ironstone beds. The sandstones occur as two sandstone bodies (Simpson,
1954 and Reyment, 1965) representing the Afikpo Sandstone, embedded within the dominantly shaly sequence
(Figure 2). The stratigraphically lower member lies unconformably on the Eze-Aku Group (Figure 1, Table 1) and
underlies the hilly terrain of Afikpo town, trending eastwards across the Cross River at Ozizza and Ndibe Beach
areas. The Upper sandstone member outcrops in Owutu Edda area trending east – west but turns southwards to
Ohafia area (Figure 1). The Nkporo Formation and its sandstone Members in the Afikpo Sub-basin lie uncomfortably
on the Turonian Amasiri Sandstone of the Eze-Aku Group (Simpson, 1954).
The paleoenvironments of deposition of the Nkporo Formation has variously been interpreted grossly as shallow
marine and brackish water solely based on fossil and palynological evidences extracted from the shaly lithofacies of
the formation (Reyment, 1965; Simpson, 1954; Mode, 1991; Petters and Edet, 1996; Odebode, 1986). The sandstone
lithofacies designated as the Afikpo Sandstone by Shell D,arcy Geologist (Simpson, 1954) has hardly been
investigated with respect to its depositional environments.
The purpose of this study is to reconstruct the paleodepositional environment of the Nkporo Formation by
identifying and describing the different lithofacies and also analyze the shapes and forms of vein quartz pebbles in
the sandstone lithofacies with diameters between 5.00 mm – 2.25 mm, and to use the results to evaluate the
paleodepositional environment of the Nkporo Formation.
2. Geological Setting
The Anambra Basin and a smaller Afikpo Sub-basin was installed simultaneously as flexural basins relative to the
Abakaliki Anticlinorium after the Santonian squeeze. The study area generally referred to as the “Afikpo Syncline”
rests uncomfortably on the folded pre - Santonian Abakaliki Anticlinorium, filled with pre-Santonian sediments of
the Asu River Group and the Eze-aku Group (Murat, 1972). The syncline, a narrow asymmetrical depression, gently
plunging southwards, is aerially flanked in the north and northwest by the Abakaliki Fold Belt (Anticlinorium), in the
east by the Calabar Flank and in the south by the Niger Delta (Figure 2).
Reyment (1965) and Murat (1972) described the stratigraphy of the Anambra Basin and the Afikpo Syncline and
noted that sedimentation was controlled dominantly by transgressions and regressions which led to deposition in a
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2. Journal of Environment and Earth Science www.iiste.org
ISSN 2224-3216 (Paper) ISSN 2225-0948 (Online)
Vol 2, No.6, 2012
wide variety of environments ranging from fluvial through fluvio-marine to marine environments (Short and Stauble,
1967). The basal lithostratigraphic unit of the Afikpo Sub-basin is the Nkporo Formation, conformably overlain by
the Mamu Formation, Ajali Sandstone and the Nsukka Formation. Table 1 shows the Lithostratigraphic framework
of the sub-basin highlighting the sandstone members under study.
3. Methodology
Lithofacies characterization (analysis) method employed in this study involved the description and logging of well
exposed sections. The lithotypes, sedimentary structures, textures, bed thicknesses and contact types as well as fossil
contents were recorded. Lithologic logs of selected sections exhibiting important sedimentological features of the
rocks were arranged as composite lithologs, highlighting the different lithofacies used for paleoenvironmental
interpretation.
The pebble morphometric method of Sneed and Folk (1958) adopted by Dobkins and Folk (1970), Sames (1966),
Lutig (1962), Nwajide and Hoque (1982) have been used in this study. In this method, measurements of the three
mutually perpendicular diameters (axes) of each pebble using the veneer caliper were done. The method where the
long axis (L), intermediate axis (I) and short axis (S) are imagined to represent the internal diameters of a rectangular
box into which the pebble just fits into was used. Pebbles (vein quartz species 5.00 mm – 23.00 mm in size) collected
from logged outcrop sections of the Afikpo Sandstone Member of the Nkporo Formation were used in this study.
These pebbles were found to be very abundant as dispersed pebbles and thin beds in the pebbly, cross stratified
sandstone units and Ophiomorpha burrowed cross bedded sandstone units of the Formation. Sampling was done in
such a way as to represent all the two facies hosting pebbles (Figure3). Fifteen largest pebbles extracted from the
sandstone beds were sampled out of which the best ten were selected to form a batch for analysis. Three hundred and
forty (340) pebbles were assembled into thirty four (34) batches and studied for morphometric indices. Two hundred
(200) pebbles assembled into twenty (20) batches were studied from the lower sandstone unit at Afikpo while one
hundred and forty (140) pebbles (14 batches) were studied from the upper sandstone unit at Owutu Edda.
4. Results
4.1 Lithofacies Characterization
Walker (1984) defined facies as a body of rock showing lateral variations in the aspects of defined lithological
characteristics. On the basis of this, and to achieve simplicity, objectivity, repeatability and comprehensiveness,
seven (6) lithofacies have been recognized in the Nkporo Formation as follows (1) trough cross-bedded sandstone,
(2) Ophiomorpha burrowed, wave/rippled and planar cross-bedded lithofacies, (3) horizontal bedded/laminated
sandstones and heterolithics, (4) Very fine grained, silty sandstone (5) coals/carbonaceous beds, (6) shales/mudstone
with limestones and oolitic ironstones beds.. These lithofacies are described below with representative figures to
illustrate their main lithological characteristics and sedimentary structures.
4.1.1. Cross – Stratified Sandstone lithofacies A
This consists of fine to very coarse, but dominantly medium to coarse grained sandstones with thick cross–stratified
bedsets (Figures 3a & 3b). The main characteristic is cross-bedding and exhibits both upward fining grain size
motifs. In the fining upward parts, sharp and scoured erosive basal contacts, most often lined with vein quartz
pebbles and clay chips, are common. The cross-beds vary from trough to planar with graded foreset laminae and
scattered vein quartz pebbles. Occasionally, this lithofacies exhibits bi-directional foreset beds (herringbone
structures), clay draped foresets, graded foresets and reactivation structures with tidal bundles. Fine to very coarse
but dominantly very coarse grained, massive to poorly stratified sandstone beds with scattered pebbles are associated
with this lithofacies. They are poorly sorted with local admixed clay clasts. Internal erosional surfaces are common
with subtle fining upward motifs. This lithofacies has been interpreted as tidal channel point bars in bayhead delta.
This lithofacies dominates the lower sandstone body outcropping in Afikpo, Ndibe and Oziza areas.
4.1.2 Ophiomorpha burrowed, wave/rippled and planar cross-bedded lithofacies B
This lithofacies contains prominent Ophiomorpha isp burrows as well as cross-stratified bedsets (Figure 4). The
lithofacies is fine to very coarse grained with dispersed pebbles; poorly sorted and planar cross-bedded. Ripple
bedforms and sandwaves (megaripples) exhibiting symmetrical geometry are common. The Ophiomorpha isp
burrows vary from vertical to sub-horizontal with lengths from 5cm to 30cm and cross sectional diameter of 1.0 – 2.0
cm. This lithofacies exhibits both fining (with scoured basal contacts) and upward coarsening motifs. Occasionally, 5
– 30 cm thick lenticular-shaped claystone beds mark the rippled contacts of the sandstones. It has been interpreted as
27
3. Journal of Environment and Earth Science www.iiste.org
ISSN 2224-3216 (Paper) ISSN 2225-0948 (Online)
Vol 2, No.6, 2012
estuary mouth beach/barrier and tidal bar deposits. This lithofacies outcrops in Owutu area and characterizes the
stratigraphically upper sandstone body.
4.1.3 Inclined Heterolithic Stratified (sand – dominant heterolithic) lithofacies C
This comprises friable, well sorted, very fine to medium but dominantly very fine to fine grained sandstones
interbedded with thinner beds of dirty white and pinkish sand-dominant heterolithics. This lithofacies is dominantly
inclined with mm – cm scale claystone laminations/beds as well as flasers (Figure 5). Few Ophiomorpha isp burrows
were recorded in this lithofacies. The bed thicknesses vary from 0.10 m to 0.50 m. The lithofacies is interpreted as
tidal point bars in the proximal part of the estuarine funnel. Outcrops occur in the sandstone quarry at Ezi-Edda, near
Owutu Edda
4.1.4 Coal/carbonaceous lithofacies D
Coal beds are ubiquitous in the lower sandstone unit. They occur as sandstones - carbonaceous shale - coal cycles
sandwiched within the cross-bedded sandstone lithofacies at Ozziza and within a shaly facies at Wowo River (along
the Afikpo – Unwana road). The presence of carbonaceous beds in this association suggests deposition in a lagoonal
(or central) setting within the estuarine funnel.
4.1.5 Very fine grained, silty sandstone Lithofacies E
This lithofacies consists of 10 cm to 50 cm thick, poorly laminated, sometimes massive, silty to very fine grained
sandstone. Distinct monocreterion isp burrows occur in this lithofacies. The absence of laminations may be possibly,
due to reworking by wave/tides or burrowing by organisms (e.g monocretarion isp burrows). The lithofacies also
contains large spherical siderite concretions/nodules and plant rootlets (rhizoliths). A 1.60 m thick bed of very fine to
medium grained, grey to dark grey sandstone with intact bivalve and gastropod shells was described within this
lithofacies (Figure 6). This lithofacies has been interpreted as estuary funnel tidal bars and sand sheets.
4.1.6 Shale and Mudstone lithofacies with interbedded limestones and oolitic beds F
This lithofacies consists of dark grey to black laminated shales and mudstones with pyrite framboids and gypsum
veins and efflorescence (Figure7). They are fossiliferous, with dwarfed/juvenile bivalves, gastropods, ammonites and
abundant foraminifera in some horizons. Cm-scale siderite nodules, mostly elliptical in shape, occasionally occur as
nodular beds/lenses or sporadically scattered nodules within the bedding planes. Small burrows suspected to belong
to the Chondrites, Paleophycus and Teichichnus isp occur in this lithofacies. Beds of brown micritic limestones (10
– 25cm thick) and siderite cemented chamositic oolitite (10 cm – 33cm) occur within the dominant laminated
shale/mudstone lithofacies This facies outcrop in Asaga Amangwu, Itim Edda, Amaiyi, Akanu Ohafia and on the
lower slopes of Enugu – Okigwe Cuesta. This lithofacies is interpreted as product of shallow, open marine shelf
deposition in a transgressive setting
4.2. Pebble Morphogenesis
The results of pebble morphometric measurements of the vein quartz pebble suites of the Afikpo Sandstone are
shown on Tables 2 and 3. The methods used in analyzing and presenting results from primary particle shape data
have been controversial (Illenberger, 1991; Illenberger, 1992a and b; Benn and Ballantyne, 1992, 1993, 1995;
Howard, 1992, 1993; Woronow, 1992; Sneed and Folk, 1958; Illenberger and Reddering, 1993). However, the
precise method of result presentation is less important than the value of the results with respect to depositional
processes that shaped the particles and their geomorphic environments of deposition.
Dobkins and Folk (1970) used large particle properties (morphometric indices) of form, sphericity and roundness
from Tahiti Nui to characterize pebbles shaped in various sedimentary environments. Graham and Midgley (2000)
noted that morphometric parameter of form, roundness and sphericity provide means of differentiating facies,
providing clues about the transport history of the sediment, and characterizing depositional environments. In this
study, morphometric indices of maximum projection sphericity, oblate prolate index, coefficient of flatness and
elongation indices regarded as environment - sensitive have been employed in the interpretation of the
paleoenvironments of the Sandstone units of the Nkporo Formation. The relevant parameters used are:
- Coefficient of Flatness, S/L (Stratten, 1974; Els, 1988).
- Elongation Ratio, I/L (Sames, 1966; Lutig, 1962).
- Maximum Projection Sphericity (S2/LI) 1/3 (Sneed and Folk, 1958) .
- Oblate – Prolate Index. (OPI) 10{(L – I)/L – S) - 0.50} / {S/L} (Dobkins and Folk, 1970)
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4. Journal of Environment and Earth Science www.iiste.org
ISSN 2224-3216 (Paper) ISSN 2225-0948 (Online)
Vol 2, No.6, 2012
- Form, (L – I / L – S) (Sneed and Folk, 1958). The shapes were obtained using the triangular Sphericity -
Form Diagram of Sneed and Folk (1958).
- The roundness of each pebble was estimated using Sames (1966) Pebble Image Set.
- The mean and standard deviation for the morphometric indices were calculated using the statistical
formulae as follows
Pebble suites from the stratigraphically lower unit at Afikpo have coefficient of flatness ratio (FR) varying from 0.46
– 0.61 with a mean value of 0.51±0.08; elongation ratio (ER) of 0.62 – 0.81 with mean of 0.71±0.10; form with
dominant compact bladed (CB) shapes and values varying from 0.44 – 0.73 with a mean of 0.58±0.15. The
maximum projection sphericity (MPS) varies from 0.64 – 0.78 with a mean of 0.71±0.07; oblate- prolate index (OPI)
range from -1.42 – 3.26 with a mean of 1.67 while roundness (ρ) varies from 30% - 46% with a mean of 39.95%.
For the upper Sandstone Member at Owutu Edda, the pebble suites measured have coefficient of flatness (FR) of
0.35 - 0.50 with a mean of 0.42; elongation ratio (ER) of 0.67 - 0.78 with a mean of 0.73 and form index of 0.38 -
0.58 with a mean of 0.47 and dominant bladed (B) shapes. The maximum projection sphericity (MPS) varies from
0.56 - 0.70 with a mean of 0.63; the oblate-prolate index (OPI) varies from -3.13 - 2.04 with a mean of -0.69 while
roundness (ρ) ranges from 50% - 71% with a mean value of 56%.
5. Interpretation and Discussion
S5.1 Lithofacies Association
Based on the lithofacies and their characteristics, the entire Nkporo Formation has been grouped into two lithofacies
associations – the estuarine lithofacies association and partially anoxic shallow marine shelf association. Figure 8
shows a composite lithologic log (450 m thick) with the lithofacies and the associations. The estuarine lithofacies
association clearly shows a tripartite subdivision into a lower section of estuary tidal channels and point bars, middle
section of estuary funnel dominated by estuarine subtidal point bars, silts and lagoonal (carbonaceous) shales and an
upper section of estuary mouth complex and inlet deposits (Dalrymple et al., 1992; Allen and Posamentier, 1993;
Miall, 2000; Shanmugam et al, 2000; Catunuanu, 2006 and Nicols, 2009). The lower sandstone units have been
interpreted as tidal channel point bars in upper estuarine delta setting. The presence of herringbone and tidal bundles
with reactivation structures support this interpretation. The inclined bedded / laminated sand –dominant heterolithic
lithofacies (IHS), the carbonaceous/coals and very fine silty sandstone facies were deposited in the estuarine funnel
(Nicols, 2009, p. 210). The Ophiomorpha isp burrowed and planar cross-bedded lithofacies with wavy beds, ripples
and dunes bedforms were deposited as beach/barrier and tidal sand bars deposits in the estuary mouths (Catenuanu,
2006, p. 149). The presence of wave and tide structures is noteworthy in this lithofacies. The coal and carbonaceous
beds association, with the very fine grained and silty lithofacies belong to central estuarine funnel setting. The
association of dark grey to black shales with micritic limestone and oolitic (sideritic) ironstone is interpreted as
products of shallow marine shelf deposition in a transgressive setting (Nwajide and Reijers, 1996). The presence of
siderite nodules, pyrites, dwarfed ammonites and chamosite oolitic ironstones, supported deposition in partially
anoxic marine settings (Maynard, 1983, p. 42, 46).
5.2. Pebble Morphometric interpretation.
Several authors have demonstrated the usefulness of pebble morphometric parameters in paleoenvironmental
interpretations (Dobkins and Folk, 1970; Lutig, 1962; Sames, 1966; Stratten, 1974; Els, 1988; Illenberger and
Reddering, 1993 and Barret, 1980). As independent functions, the coefficient of Flatness (FR), Elongation Ratio
(ER), Maximum Projection Sphericity (MPS), Oblate-Prolate Index (OPI), Roundness (ρ) and Form have been used
as indices for environmental diagnosis. As dependent variables, scatter plots of maximum projection sphericity
(MPS) versus oblate-prolate index (OPI) and roundness (ρ) versus elongation ratio (ER) are also useful in
discriminating the environments of deposition.
Dobkin and Folk (1970) studied pebbles shaped by river and beach processes in Tahiti-Nui and noted that the mean
sphericity of fluvial pebbles is 0.684 while mean sphericity of pebbles in low energy and high energy beaches are
0.0.640 and 0.584 respectively. On the basis of this study, they suggested that pebble suites with mean sphericity of
0.65 and less indicates beach processes while those with sphericity values above 0.65 are shaped by fluvial
processes. The pebble suites from the lower unit of the Afikpo Sandstone with maximum projection sphericity
varying from 0.67 – 0.78 and a mean of o 0.71 are therefore interpreted as product of a fluvial process.
The OP-Indices ranging from -1.02 – 5.06 are also suggestive of fluvial transport. Stratten (1974) used coefficient of
flatness (% Flatness ratio) to discriminate between fluvial and beach pebbles. He noted that fluvial pebbles have
coefficient of flatness of 45% and above. On this basis, the coefficient of flatness for the Afikpo Sandstone pebble
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5. Journal of Environment and Earth Science www.iiste.org
ISSN 2224-3216 (Paper) ISSN 2225-0948 (Online)
Vol 2, No.6, 2012
suites range from 45% - 61% with a mean of 51% corroborate fluvial action as the dominant depositional process.
Dobkin and Folk(1970) identified shape classes (Form) of Sneed and Folk (1958) that are diagnostic of certain
environments. Compact (C), compact bladed (CB), compact elongate (CE) and elongate (E) pebbles are diagnostic of
fluvial environments, while platy (P), bladed (B), very bladed (VB) and very platy (VP) are more common in beach
environments. The mean form index of 0.58 and compact bladed (CB) forms (and Table 2) of the pebble suites
studied in the Afikpo Sandstone further support dominant fluvial shaping with for the grains.
Roundness is a poor indicator of environment. The roundness of pebbles under hydrodynamic transport has been
observed to be a function of both inherited and acquired (environmental) factors (Sneed and Folk 1958; Lutig, 1962;
Sames, 1966 and Dobkins and Folk, 1970). Sneed and Folk (1958) observed that pebble roundness increases
downstream from rivers to the beaches for vein quartz pebbles. Roundness of less than 35% typifies fluvial
environments while roundness greater than 45% characterizes littoral environments (Sames, 1966). Therefore an
upper limit for roundness index in fluvial environments has been placed at 45%. The mean roundness index for the
lower unit of the Afikpo Sandstone pebble suites is 39.95% with 80% of the pebble suite having roundness varying
from 30 – 43%. This strongly suggests deposition in fluvial a environment (see Table 2).
Dobkin and Folk (1970) and Sames (1966) used plots of maximum projection sphericity (MPS) versus oblate -
prolate index (OPI) and roundness (Ρ) versus elongation Index (ER) respectively to discriminate environments. Plot
of MPS versus OPI confirms that the lower sandstone unit was deposited in essentially fluvial setting (Figure 9a).
The plot of roundness (Ρ) versus elongation ratio (ER) indicates deposition in transitional environment (Sames,
1966) (Figure 9b), possibly suggesting some marine influence. In all, morphometric indices show that the
stratigraphically lower unit of the Afikpo Sandstone was essentially deposited by fluvial processes.
For the upper sandstone unit outcroping in Owutu Edda area, the maximum projection sphericity (MPS) of 0.56 –
0.64 with a mean of 0.63± suggest that the pebbles were largely shaped by surf (beach) processes. The coefficient of
flatness (% FR) of 35% - 45% and all bladed (B) suites of pebbles confirm deposition in environments dominated by
beach processes (Stratten, 1974; Dobkins and Folk, 1970). The mean roundness index (Ρ) indicated for the sandstone
is 56% (Table 3). According to Sames (1966), this indicates deposition in littoral (beach) environment.
Plot of roundness (Ρ) versus elongation ratio (ER) supports deposition of the sandstone in littoral (beach)
environment (Figure 10b). However, plot of maximum projection sphericity (MFS) versus oblate - prolate index
(OPI) is not diagnostic but indicates that 36% of the pebble suites were shaped by beach processes, 36% by fluvial
processes while 28% are non-diagnostic (Figure 10a).
6. Depositional Model
Based on the depositional environments interpreted from pebble morphometry, lithofacies/associations, and their
vertical facies distribution, an estuarine delta depositional model is proposed for the Nkporo Formation. The
stratigraphically lower sandstones buried in the estuary muds represent tidal channel point bar and tidal creeks.
The stratigraphically upper sandstones interbedded within marine shales represent beach/barrier bars, tidal sand bars
and inlet deposits in a tide-wave influenced estuary mouth Complex (Figure 11). The dark grey to black shales
interbedded with limestones and oolitic beds were deposited as partially anoxic shallow marine shelf deposits.
The Nkporo estuarine delta may have developed, possibly due to falling eustatic sea levels and basin-ward shift of
base level resulting in fluvial incision and erosion of the sub-aerially exposed shelf, following the Santonian uplift
(Murat, 1972). The transgressions (base level rise) during the late Campanian resulted in submergence of the incised
valleys and deposition of estuarine facies of the Nkporo Formation. As base-level rise slowed, the net rate of
sediment supply dominated over eustatic rise, and coarse sediments were trapped at the estuary mouths while the
shelf was starved of sediments. The Afikpo Sandstone Member and indeed the entire Nkporo Formation therefore
represents estuarine and tidal point bars, tidal inlets, carbonaceous beds, estuary mouth barriers and tidal sand bars in
a submerged/drowned river valley system (Figures 3 & 4) (Nicols, 2009).
7. Conclusions
Pebble morphometric indices of sphericity (MPS), oblate-prolate index (OPI), flatness index (FR), elongation index
(ER), roundness (Ρ) and form have proved useful, together with lithofacies characteristics, in deciphering the
depositional environments of the sandstone lithofacies of the Nkporo Formation. The stratigraphically lower
sandstone Member was deposited dominantly by fluvial/tidal systems with minor marine influence, possibly as
estuarine tidal/fluvial point bars in the lower delta plain setting. The upper sandstone Member, on the other hand,
was deposited under marine environmental conditions, possibly in the surf zone or littoral setting as beach/barrier
bars and tidal delta sandbodies. The upper Sandstone Member exhibits finer grain size for its pebbles than those of
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the lower Sandstone unit. This may support deposition in a more distal environmental setting, downstream of rivers
that transported the pebbles from the hinterland source regions.
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Fig. 1 Fig. 2
Figure 1: Geological Map showing the Nkporo Formation with the sandstone members
Figure 2: Structural framework of southeastern Nigerian sedimentary basin (After Murat, 1972)
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Lithostratigraphic Unit
Age Basin
Formations Members
Nsukka Fm.
Late Maastrichtian
Middle
Afikpo Sub- basin
Ajali Fm.
Maastrichtian
Mamu Fm.
Early
Late Cretaceous
Maastrichtian Nkporo Shale
Afikpo Sandstone
Nkporo Fm. Nkporo Shale.
Late Campanian
Afikpo Sandstone
Santonian angular unconformity
Turonian Ezeaku Group
Benue/ Abakaliki
Cenomanian Odukpani Basin/ Calabar Flank
Early
Albian Asu River Group
Cretaceous
Precambrian Precambrian Basement Complex
Table 1 shows a lithostratigraphic framework for the Afikpo Sub-basin, southeast Nigeria
b
Figure 3a: Planar cross bedded sandstones with reactivation structures and tidal bundles (3b) and
herringbone structures are sandstones on the Amaorie Beach road, Ozziza, Afikpo.
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Thicknes Lithology
24.0m
Sandstone, Ophiomorpha
burrowed; m – crs
grained, pebbly on lower
contacts. Mod – poorly
Sandstone, Trough &
planar cross bedded;
med. – crs grained
with pebbles
Figure 4: Outcrop section of Afikpo Sandstone on Mcgregor Hill
20.0m
with vein quartz pebbles
Parallel & wavy bded;
sst; f – m gr
Heterolithic
unit
Covered Section
V.crs sst; trough
x-beds, pepply
lower contact
SSt, fine gr.,
parallel bedded
16.0m & lam.
Ezeaku Group
C f m cs vcs
Fig. 5 Fig. 6
Figure 5: Sand-dominant heterolithic unit with wavy and ripple laminations, flaser structures, low angle
cross-beds and rare Ophiomorpha isp burrows at the Ezzi Edda Sandstone quarry.
Figure 6: Fossiliferous Sandstone with intact bivalves and gastropod shells along Ndibe Beach Road
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Figure 7: Dark grey to black shale with beds of brownish micritic limestone.
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