Cambrian-Ordovician Periods


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Paleozoic Climate, Fauna, Flora, Tectonics and Paleoclimate, Cambrian, Ordovician,Trilobites,Graptozon,Mass Extinction

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Cambrian-Ordovician Periods

  1. 1. Stratigraphical Macropaleontology
  2. 2. What is Stratigraphical Macropaleontology ? Unit III Unit IV Unit V Unit VI Unit VII Eocene Carbonates
  3. 3. Course Title: Stratigraphical Macropaleontology
  4. 4. Course Content Introduction to the Mesozoic Era The Triassic World The Jurassic World The Cretaceous World Introduction to the Cenozoic Tertiary -Paleogene Tertiary - Neogene Upper Paleozoic World Permian Carboniferous Middle Paleozoic World Devonian Silurian. Lower Paleozoic World Ordovician Cambrian Introduction to the Paleozoic Era
  5. 5. Paleozoic Stratigraphy eon era period when began myrs ago ICS duration myrs ICS Phanerozoic Mesozoic Triassic 251 51 Paleozoic Permian 299 48 Carboniferous 359 60 Devonian 416 57 Silurian 444 28 Ordovician 488 44 Cambrian 542 54 Proterozoic Neoproterozoic Ediacaran ("Vendian") 630 88
  6. 6. Paleozoic Climate • The Cambrian climate was probably moderate at first, becoming warmer over the course of the period, as the second-greatest sustained sea level rise in the Phanerozoic got under way. However, as if to offset this trend, Gondwana moved south with considerable speed, so that, in Ordovician time, Most of West Gondwana (Africa and South America) lay directly over the South Pole. The Early Paleozoic climate was also strongly zonal, with the result that the "climate", in an abstract sense became warmer, but the living space of most organisms of the time -- the continental shelf marine environment -- became steadily colder. However, Baltica (Northern Europe and Russia) and Laurentia (eastern North America and Greenland) remained in the tropical zone, while China and Australia lay in waters which were at least temperate. The Early Paleozoic ended, rather abruptly, with the short, but apparently severe, Late Ordovician Ice Age. This cold spell caused the second-greatest mass extinction of Phanerozoic time. • The Middle Paleozoic was a time of considerable stability. Sea levels had dropped coincident with the Ice Age, but slowly recovered over the course of the Silurian and Devonian. The slow merger of Baltica and Laurentia, and the northward movement of bits and pieces of Gondwana created numerous new regions of relatively warm, shallow sea floor. As plants took hold on the continental margins, oxygen levels increased and carbon dioxide dropped, although much less dramatically. The north-south temperature gradient also seems to have moderated, or metazoan life simply became hardier, or both. At any event, the far southern continental margins of Antarctica and West Gondwana became increasingly less barren. The Devonian ended with a series of turnover pulses which killed off much of Middle Paleozoic vertebrate life, without noticeably reducing species diversity overall. • The Late Paleozoic was a time which has left us a good many unanswered questions. The Mississippian Epoch began with a spike in atmospheric oxygen, while carbon dioxide plummeted to unheard-of lows. This destabilized the climate and led to one, and perhaps two, ice ages during the Carboniferous. These were far more severe than the brief Late Ordovician Ice; but, this time, the effects on world biota were inconsequential. By the Cisuralian, both oxygen and carbon dioxide had recovered to more normal levels. On the other hand, the assembly of Pangea created huge arid inland areas subject to temperature extremes. The Lopingian is associated with falling sea levels, increased carbon dioxide and general climatic deterioration, culminating in the devastation of the end-Permian extinction.
  7. 7. • Geologic Time! (mya = million years ago) Navigating Our Geology Wing Precambrian (4,500 to 543 mya) • Hadean (4500 to 3800 mya) Archaean (3800 to 2500 mya) Proterozoic (2500 to 543 mya) Vendian (650 to 543 mya) • Phanerozoic (543 mya to today) • Paleozoic Era (543 to 248 mya) • Cambrian (543 to 490 mya) Tommotian (530 to 527 mya) • Ordovician (490 to 443 mya) Silurian (443 to 417 mya) Devonian (417 to 354 mya) Carboniferous (354 to 290 mya) • Mississippian (354 to 323 mya) Pennsylvanian (323 to 290 mya) • Permian (290 to 248 mya) • Mesozoic Era (248 to 65 mya) • Triassic (248 to 206 mya) Jurassic (206 to 144 mya) Cretaceous (144 to 65 mya) Cenozoic Era (65 mya to today) • Tertiary (65 to 1.8 mya) Paleocene (65 to 54.8 mya) Eocene 54.8 to 33.7 mya) Oligocene (33.7 to 23.8 mya) Miocene (23.8 to 5.3 mya) Pliocene (5.3 to 1.8 mya) Quaternary (1.8 mya to today) Pleistocene (1.8 mya to 10,000 years ago) Holocene (10,000 years ago to today)
  8. 8. The Paleozoic systems may be defined in terms of Some distinctive form of life: Permian = primitive reptiles. U. Paleozoic Pennsylvanian = Lycopod plants(scale trees) and amphibians. Mississipian = Brachiopods and Bryzoa. Devonian = Tetracorals and Fishes. Silurian = Tabulate Corals. L. Paleozoic Ordovician = Graptozon & Cystoids. Cambrian = Trilobites. The Paleozoic is divided into two:- Upper Paleozoic = Age of Ferns and Vertebrates. Lower Paleozoic = Age of Algae and invertebrates.
  9. 9. The Cambrian Period 543 to 490 Million Years Ago • The Cambrian Period marks an important point in the history of life on earth; it is the time when most of the major groups of animals first appear in the fossil record. This event is sometimes called the "Cambrian Explosion", because of the relatively short time over which this diversity of forms appears. It was once thought that the Cambrian rocks contained the first and oldest fossil animals, but these are now to be found in the earlier Vendian strata.
  10. 10. The Cambrian Period (from a Latin form of the Welsh name for Wales) begins the Paleozoic Era about 544 mya, and comes to a close about 490 mya. it was during the Cambrian that life "exploded," developing almost all of the major groups in a relatively short time. Originally, the bottom of the Cambrian was defined as the point where fossils began. Subsequently, older fossils have been found, and this definition is no longer valid. Now, it is roughly determined to be the point at which there is the first appearance of numerous fossil shells Duration: 54 millions years Maximum thickness : 40,000 feet. Cambrian ( SEDGWICK 1835) from Cambria = Wales. The Pre-Cambrian ended with the Huronian orogeny which raised the land into dominant mountains, after this formation , these Huronian mountains were subjected to prolonged period of intensive erosion lowered them into a peniplain ., over this , the lower Paleozoic (Cambrian) are gradually transgressed.
  11. 11.  Cambrian: Facies The Cambrian exposures are well represented in the basin ranged of Utah and Nivada. The Lower Cambrian deposits consists chiefly of Quartzite. Some zones are shally, other are calcareous, but the sandy sediments are remarkable. These sands derived from the crystalline Pre-cambrian rocks.Most of these deposits are marine due to the presence of Trilobites and other annelid fossils . The Middle Cambrian formations are mainly L.s The Upper Cambrian series is largely dolomitic L.S. with Trilobites Significant Events • The Cambrian Explosion • There is currently some debate concerning the rapidity of life form developments during the Cambrian Period but, regardless, it was during this time that almost all of the major life form types appeared on Earth. • Mass Extinction • The Cambrian ended with a mass extinction of about 75% of the trilobite families, half the sponge families, and many brachiopods and snails. The cause of the extinction is not known
  12. 12. Cambrian Graphics ArthropodTrilobiteBrooksella
  13. 13. EldoniaDinomischsTrilobite
  14. 14. Subdivisions of the Cambrian: -The chart at left shows the major subdivisions of the Cambrian Period for North America (Laurentia during the Cambrian). -International ages (subdivisions) have not been established. -The size of the bars does not correlate with the length of time for each age. The oldest unnamed age is 543 to 520 million years ago, while the remaining six ages are from 520 to 490 million years ago, each approximately 5-6 million years long. This chart is mapped to allow you to travel back to the Vendian, or forward to the Ordovician. You may also click to see our close-up look at the Tommotian. The Cambrian Period is part of the Paleozoic Era. The Paleontological classification of the system is based upon the vertical distribution of Trilobites. -Three stages have been distinguishes in two geographic provinces:- -------------------------------------------------------------------------------------------------------------- Stages Atlantic Provinces Pacific Provinces -------------------------------------------------------------------------------------------------------------- • Upper Cambrian= Potsdamian Olenus Dikellocephalus • Middle Cambrian = Acadian Paradoxides Ptychuparia • Lower Cambrian = Georgian Olenellus Olenellus -----------------------------------------------------------------------------------------------------------------
  15. 15. Cambrian:Stratigraphy 1. A lot can happen in 40 million years, the approximate length of the Cambrian period. Animals showed dramatic diversification during this period of Earth's history. This has been called the "Cambrian Explosion". When the fossil record is scrutinized closely, it turns out that the fastest growth in the number of major new animal groups took place during the Tommotian and At dabanian stages of the Early Cambrian, a period of time which may have been as short as five million years! In that time, 2. the first undoubdted fossil annelids, arthropods, brachiopods, echinoderms, molluscs, onychophorans, poriferans, and priapulids show up in rocks all over the world. Perhaps we should call this bit of time the "Tommotian Explosion".
  16. 16. Cambrian: Life • The dominant creatured of the Cambrian seas were Trilobites (60% of the fauna). Next to the Trilobites in importance , came Brachiopods(30% ). • More than 1.5oo species of the invertebrates are known in the Cambrian, all marine, of which 60% are trilobites, and 30% brachiopods. Calcareous Sponges were also reef building organisms. Vertebrates and land plants were not represented. Blue – green algae were abundant, they form limy reefs. • Life was entirely marine during the Cambrian Period. It includes representatives of all groups of the animal kingdom except vertebrates and thus the Cambrian does not mark the down of life on the Earth. • The most characteristic animals of the Cambrian period were the trilobites, a primitive form of arthropod remarkable for it's highly developed eyes (unusual  Fauna: • Archiocyathids: They are reef building organisms , characteristic • of the upper part of Cambrian( Archaeocyatha The Archaeocyatha or archaeocyathids were sessile, reef-building marine organisms of warm tropical and subtropical waters that lived during the early Cambrian period • Calcareous Algae: were widely spread reef builders,e.g. Creptozoon • Calcareous Sponges: were also reef building organisms characteristics of the upper part of the Lower Cambrian. • Brachiopods: abundant inarticulate Brachiopods such as Lingula and Obelus in sandy litteral facies indicating old beaches. • Trilobites: they are the most important fossils in Cambrian rocks,e.g. Paradoxides, Olenellus, Olenus • Gastropods: recorded since the lower Cambrian becoming important by the end of the period
  17. 17. Paleogeography of the Cambrian • The Cambrian rocks are separated from the older ones by on of the most remarkable unconformities. • The Paleogeographic picture for the beginning of the lower Paleozoic is as follows: • A number of continental masses corresponding to the various shields which were folded in the Huronian movement were lowered down after prolonged period of erosion. Over these folded Pre- Cambrian rocks, the sea of the Paleozoic advanced. • The Cambrian sea expanded continously and flooded the low-land. It is the first system to contain fossils that allow correlation between distant regions. • The Cambrian ocean was covering what are now Pacific Ocean, central and northern Australia, eastern and central Asia and nearly all Europe :but the northern part of the Atlantic ocean being communicated with pacific ocean across panama. • A southern continent Gondwana Land was existing comprising what are now south America, Africa, Arabia, the western half of India and west Australia, all having in connection.
  18. 18. • Cambrian: Localities • Rocks of Cambrian age are distributed in the Great Basin of the western United States, parts of the northeastern United States, Wales, Scandinavia and the Baltic region, Siberia, and China, among other places. These localities were not where they are now: the position of the continents was very different. It may seem strange to imagine California on the equator, or Venezuela near the South Pole, but that's how things were! Check out this map to learn more! • Cambrian localities on this server: (see map above) • Aldan River - Lower Cambrian fauna from this site in Yakutia, Siberia, trace the early evolution of animals with skeletons. • Burgess Shale - One of the greatest fossil finds ever made is the Burgess fauna of British Columbia. Thousands of soft-bodied animal fossils paint us a picture of early marine life. • House Range, Utah - A varied array of Cambrian critters has been found in the Wheeler Shale and the Marjum Formation, both of which are exposed in the House Range. • Marble Mountains - In the hottest part of the Mojave Desert of California is the rich Latham Shale where Olenellid trilobites are numerous. • White-Inyo Mountains - You can visit ancient reefs in the mountains of eastern California. • Information about Cambrian localities from other websites: Paleontology Portal: the Cambrian - Learn more about the Cambrian paleontology and geology of North America. • Burgess Shale fossils - This Middle Cambrian site in present-day British Columbia is known for its excellent preservation of soft-bodied invertebrates. The website is maintained by the University of Calgary. • Strange Creatures - A Burgess Shale Fossil Sampler - Another website about these unusual critters, this one from the Smithsonian. Cambrian: Localities
  19. 19.  The Cambrian rocks are known as a-Continental facies b-Geosynclinal facies They are found in the following areas:- • The border zone of the in Baltic shield • The border zone of the in Hebrides • In N. Europe in the geosynclinal zone. • N. America around the Canadian shield • In Mediterranean geosynclinal zone (Moracoo, Sardinia,..) • In Atlantic area • In Pacific area • In Egypt • Um Bogma-Abu Durba----Sinai • Western Desert (Northern part)[ Gib Afia, Ghazalat; • Betty, Bhariya Wells} the most important fauna is Trilobites
  20. 20. Cambrian: Tectonics and Paleoclimate • The Cambrian follows the Vendian period, during which time the continents had been joined in a single supercontinent called Rodinia (from the Russian word for "homeland", rodina). As the Cambrian began, Rodinia began to fragment into smaller continents, which did not always correspond to the ones we see today. The reconstruction below shows the rifting of Rodinia during the Tommotian. Green represents land above water at this time, red indicates mountains, light blue indicates shallow seas of the continental shelves, and dark blue denotes the deep ocean basins. (For clarity, the outlines of present-day continents have been superimposed on the map.) • Zones of climate were poorly defined. The temperature of the seas were mild, temperate or warm i.e higher and much ore uniform over great distances north and south of the equator than it is now.
  21. 21. This reconstruction shows the rifting of Rodinia. Green represents land above water at this time, red indicates mountains, light blue indicates shallow continental shelf seas, and dark blue denotes the deep ocean basins. (For clarity, the outlines of present-day continents have been superimposed on this map.)
  22. 22. • As you can see, the Cambrian world was concentrated in the southern hemisphere. The largest landmass (lower right) was Gondwana (a collection of today's southern continents). The second largest continent, Laurentia is just left of center in the map below, and includes most of North America (the southeastern US can be seen wedged between Africa and South America as part of Gondwana). Between Gondwana and Laurentia lie Siberia (just south of the equator) and Baltica (Scandinavia, eastern Europe, and European Russia). The rest of Europe and much of what is today Asia lay in fragments along the north coast of Gondwana. • These landmasses were scattered as a result of the fragmentation of the supercontinent Rodinia that had existed in the Late Proterozoic. Laurentia stradled the equator, while Baltica and Siberia were southeast of that continent. Tectonism affected regions of Gondwana is what are presently Australia, Antarctica, and Argentina the most. This is evident because of the presence of volcanic island arcs, which show that seafloor spreading and crustal subduction occurred. The continental plate movement and collisions during this period generated pressure and heat between continents. this resulted in the folding, faulting, and crumpling of rock which formed large mountain ranges. • The Cambrian world was bracketed between two ice ages, one during the late Late Proterozoic and the other during the Ordovician. During these ice ages, the decrease in global temperature led to mass extinctions. Cooler conditions eliminated many warm water species, and glaciation lowered global sea level. However, during the Cambrian there was no significant ice formation. None of the continents were located at the poles, and so land temperatures remained mild. In fact, global climate was probably warmer and more unifrom than it is today. With the beginning of the Cambrian at the retreat of Proterozoic ice, the sea level rose significantly. Lowland areas such as Baltica were flooded and much of the world was covered by epeiric seas. This event opened up new habitats where marine invertebrates, such as the trilobites, radiated and flourished. • Plants had not yet evolved, and the terrestrial world was therefore devoid of vegetation and inhospitable to life as we know it. Photosynthesis and primary production were the monopoly of bacteria and algal protists that populated the world's shallow seas. • Also during the Cambrian, oxygen first mixed into the world's oceans in significant quantity. Although there was plentiful atmospheric oxygen by the opening of the Cambrian, only in the Cambrian did the numbers of oxygen- depleting bacteria reduce in numbers sufficiently to permit the high levels we know today. This made dissolved oxygen available to the diversity of animals, and may have triggered the "Cambrian Explosion". This was when most of the major groups of animals, especially those with hard shells, first appear in the fossil record
  23. 23. The Tommotian Age 530 Million Years Ago • The Tommotian Age, which began about 530 million years ago, is a subdivision of the early Cambrian. Named for rock exposures in Siberia, the Tommotian saw the first major radiation of the animals, or metazoans, including the first appearance of a great many mineralized taxa such as brachiopods, trilobites, archaeocyathids, molluscs, echinoderms, and more problematic forms. Soft-bodied members of many other phyla were also appearing and diversifying at this time. A few million years before the Tommotian, in the Vendian, the continents had been joined in a single supercontinent called Rodin (from the Russian word for "homeland", rodina.) As the Cambrian began, Rodinia began to fragment into smaller continents which did not always correspond to the ones we see today. Much later, in the Permian, the continents came back together to form a new supercontinent, called Pangaea.
  24. 24. All fossils in the Cambrian • Emeraldella © 2002 Acrothele subsidua © 2005 Lingulella © 2003
  25. 25. Stromatolite © 1998 Albertella cf. longwelli Albertella © 2003
  26. 26. Altiocculus harrisi © 2005 Asaphiscus wheeleri © 1998
  27. 27. Asaphiscus wheeleri © 2005 Bathyuriscus fimbriatus © 2005
  28. 28. Cedaria minor © 2002 Modocia © 2003
  29. 29. Dikelocephalus © 2003 Modocia weeksensis © 2005
  30. 30. Olenellus (Paedeumias) clarki © 2004 Olenoides nevadensis © 2005
  31. 31. Extinction Processes • Extinction strikes in both the land and the sea. • On the land, while animals suffer repeatedly, plants tend to be highly resistant to mass extinctions. • Preferential disappearance of tropical forms of life during mass extinctions. • Tendency of certain groups of animals to experience them repeatedly (for example, trilobites and ammonoids). • Alleged equal spacing, or periodicity in geological time (occurring about every 26 million years). • These similarities between distinct extinction occurrences aid paleontologists in determining the agents the agents that perpetuated the disappearances of species in each extinction event. Such agents are currently divided into two types: • Catastrophic Agents- such as meteorite impacts and comet showers, • Earth Agents- such as volcanism, glaciation, variations in sea level, global climatic changes, and changes in ocean levels of oxygen or salinity • Although these agents can explain mass extinction, the causes of mass extinction events remains relatively unknown.
  32. 32. The Precambrian and Vendian Mass ExtinctionsFast Facts • - Precambrian period • (4.500 million to 523 million years ago) - Vendian period (4.500 to 543 million years ago) . • - Both Precambrian and Vendian periods host to at least one mass extinction each -Speculated Causes of the Precambrian and Vendian Extinctions • The first extinction of the Precambrian, which largely affected stromatolites and acritarchs, has been correlated with a large glaciation event that occurred about 600 million years ago. This event was of such severity that almost all micro-organisms were completely wiped out. • The Vendian extinction, occurring near the close of the Vendian period, is currently under debate as to whether an extinction event occurred or not. Many paleontologists believe that the Vendian fauna were the progenitors of the Cambrian fauna. However, others believe that the Vendian fauna have no living representatives. Under this latter hypothesis, the Vendian fauna is believed to have an undergone an extinction, after which the Cambrian fauna evolved. Until more information can be collected, details on the Vendian extinction event will remain open to debate • The Cambrian Mass Extinction -The Cambrian period ranges from 543-488 million years ago - The most important animal group of the Cambrian were the trilobites -Three mass extinctions occurred during the course of the Cambrian
  33. 33. The Cambrian Mass Extinction • Fast Facts • The Cambrian period ranges from 543-488 million years ago • The most important animal group of the Cambrian were the trilobites • Three mass extinctions occurred during the course of the Cambrian
  34. 34. Speculated Causes For the Cambrian Extinction • The two most accepted current hypotheses for the Cambrian extinction are: 1-Glaciation in the early Ordovician 2-Cooling and depletion of oxygen in marine waters
  35. 35. 1-Glacial Cooling Hypothesis • The advancement of the theory of glaciation as the predetermining agent for the Cambrian extinctions has been developed by James F.Miller of Southwest Missouri State University. Through research undertaken by Miller, evidence of early Ordovician sediment of glacial origin has been uncovered in South America. • Miller suggests in his hypothesis that this evidence of continental glaciation at the Cambrian-Ordovician boundary is responsible for a decrease in global climatic conditions. Such a decline in temperature is implied by Miller to destroy Cambrian fauna which are intolerant of cooler conditions, producing a mass extinction of mostly warm water species. • He also suggests that a significant continental glaciation would bring large amounts of ocean water onto the land in the form of frozen glacial ice. This trapping of ocean water inevitably results in the decrease of sea-level and the withdrawal of shallow seas. Miller implicates that this reduction in sea-level would produce reduced habitat for marine species as continental shelves are obliterated. Ecological competition would consequently ensue, perhaps acting as a driving agent for extinction. • 2-Oxygen Depletion Hypothesis • The development of a hypothesis invoking the cooling and depletion of water in marine waters as a causative agent for the Cambrian extinctions has been advanced by several geologists, primarily Allison Palmer and Michael Taylor of the U.S. Geological Survey and James Stilt of the University of Missouri. • The cooling and oxygen depletion would occur when cool waters from deep zones of the ocean spread up onto the continent, eliminating all organisms not able to tolerate cool conditions. The cooling would also result in stratification of the water column. • Thus, species would ultimately perish due to their inability to tolerate dramatic shifts in such limiting factors as temperature and oxygen availibility. Further research is required to more fully test the validity of the above outlined Cambrian extinction hypotheses
  36. 36. • Duration: 44 million years • Maximum thicknes: 60,000 feet • The Ordovician Period (from the name of an ancient British tribe, the Ordovices) extended from 488 mya until 444 mya. • The Ordovician rocks cover wider areas than Cambrian, on which they commonly lie conformably. • At the end of the Cambrian, sea levels fell, causing extinctions. • The continents were moving together during this period, and mountain-building was taking place in the northeastern North American continent. The rest of the continent was relatively quiet. • Ordovician periods, thick accumulation of shallow water sands and deep water black muds were deposited in a gradually sinking floor of some seas,while carbonates were chemically or organically deposited in warm seas
  37. 37. Ordovician: Facies Deposits are mainly marine, conglomerates, grits, sandstones, shales, slates mudstones and radiolarian chets. Zoned by means of graptolite faunas. Four different facies representing different areas are well exhibited:- • Shelly facies : sandy and calcareous indicating shallow water deposits, very fossilliferous, containing Trilobites, brachiopods, corals, cystoids, and gastropods. • Dolomitic facies: being formed chemically or organically in warm and closer seas, giving rise to thick limestone and dolomite. • Graptolitic( shaly ) facies: thinner and finer sediments laid down far from the shore, containing common graptolites and abundant trilobites. • Volcanic facies: chiefly lava flows, may be interstratified with deposits of other facies, often deposited upon the ocean floor.
  38. 38. Ordovician: Significant Events • First Vertebrates • It was in the Ordovician that the first animals with backbones arose. The Agnatha, the jawless fishes, were the first animals with true bony skeletons. • Mass Extinction • The Ordovician Period ended with a mass extinction. About 25% of all families did not make it into the Silurian.
  39. 39. Ordovician Graphics Trilobite Cephalopod
  40. 40. Echinoderm Ordovician Sea
  41. 41. Mollusk Snails
  42. 42. Maclurites Endoceras Endoceras
  43. 43. The Ordovician period began approximately 490 million years ago, with the end of the Cambrian, and ended around 444 million years ago, with the beginning of the Silurian. At this time, the area north of the tropics was almost entirely ocean, and most of the world's land was collected into the southern super-continent Gondwana. Throughout the Ordovician, Gondwana shifted towards the South Pole and much of it was submerged underwater. The Ordovician 490 mya to 444 mya Million Years Ago
  44. 44. • The Ordovician is best known for the presence of its diverse marine invertebrates, including graptolites, trilobites, brachiopods, and the conodonts (early vertebrates). A typical marine community consisted of these animals, plus red and green algae, primitive fish, cephalopods, corals, crinoids, and gastropods. More recently, there has been found evidence of tetrahedral spores that are similar to those of primitive land plants, suggesting that plants invaded the land at this time. • From the Early to Middle Ordovician, the earth experienced a milder climate in which the weather was warm and the atmosphere contained a lot of moisture. However, when Gondwana finally settled on the South Pole during the Late Ordovician, massive glaciers formed causing shallow seas to drain and sea levels to drop. This likely caused the mass extinctions that characterize the end of the Ordovician, in which 60% of all marine invertebrate genera and 25% of all families went extinct.
  45. 45. Ordovician: Stratigraphy • The Ordovician was named by the British geologist Charles Lapworth in 1879. • He took the name from an ancient Celtic tribe, the Ordovices, renowned for its resistance to Roman domination. The epochs and series of the Ordovician each have a type location in Britain, where their characteristic faunas may be found. • The age of the Ordovician boundaries were determined using potassium-argon and uranimum radiometric dating. • Graptolites, extinct planktonic organisms, are most often used to correlate Ordovician strata.
  46. 46. Ordovician: Subdivisions • The boundary between the Cambrian and the Ordovician is marked by the appearance of planktic dictyonemid graptolites. • The boundary between the Ordovician and the Silurian has been designated as the base of the Parakidograptus acuminatus graptolite zone by international agreement. Dobs Linn, near Moffat, in southern Scotland is the type locality for that boundary. There, black graptolite- bearing shales are exposed Ordovician: Subdivisions The general classification of the Ordovician rocks both in Europe and North America is as follow: N.America Europe Upper Ordovician= Clincinatian = Cardocian Middle Ordovician=Champlanian =Llandelian Lower Ordovician= Canadian = Arenigian
  47. 47. Life of the Ordovician
  48. 48. Life of the Ordovician Fauna: Nearly all the important groups of the marine animals are represented. The most important members of the Ordovician fauna are the Trilobites, graptolites, and brachiopods. The fauna of the Ordovician time are much richer in species and individuals than that of the Cambrian of these the most important are: Trilobites :forming the most important Ordovician fauna attaining their climax of development in number and species e.g. Agnostus, Trinucleus, Asaphus Graptolites: widely distributed, reached their climax of development, used for zoning of Ordovician few species sediments e.g. Diplograptus, Phyllograptus, Didymograptus, Diplograptus, Tetragraptus. Brachiopods : much more abundant than the Cambrian ones, e.g. Lingula, Strophomena. Orthis. Some genera are used in subdividing the system. Corals: first appeared , both Rugose and Tabulates few species widely distributed in Late Ordovician. Mollusca: gastropods are of little stratigraphical value. Cephalopods are abundant and better represented by loosell coiled shells. Echinoderms: represented by a variety of cystoides and by numerous crinoides and the earliest known blastoides.
  49. 49. Ordovician: Climate • Rather hot and dry nearly uniform temperature condition prevailed over large portions of the globe. • No glacial formations are known Ordovician: Orogeny • Towards the close of the Ordovician , a great Taconic mountains building revolution in N. A merica . In Western Europe, the Caledonian movement which is to continue in the Silurian and Devonian makes its debut as mountain builders. . Main vlocanic activity begins in wales. Extensive submarine and subaerial volcanic activity in the British area.
  50. 50. Ordovician: Localities Ordovician localities on this server: (see map above) Canning Basin, Australia - A great diversity of fossil gastropods has been uncovered in the Canning Basin. Lake Winnipeg, Manitoba, Canada - The limestones of this region have preserved many spectactular fossils of macroalgae. In Egypt: Ordovician deposits occur : -Um Bogma-Abu Durba---Central Sinai -Western Desert (Northern part)[ Gib Afia, Ghazalat; -Betty, Bhariya Wells} the most important fauna is Trilobites
  51. 51. Paleogeography of the Ordovician • Towards the close of the Cambrian period, the seas began to retreat. The Ordovician began with a new spreading of the sea and thus the two system are separated in as in North America, there was nearly a continent sedimentation. • The distribution of Ordovician deposits clearly show that during these times, there was four continents: North Atlantic continents, Arctic Continent, Asiatic (Angara) Continent, Equatorial (Gondwana) continent. • The geography of Cambrian and Ordovician systems seems to proof the existence of what is known as • N. Alantic continent ----this was the land extending from N. America to N. Europe. • Asiatic continent was that part forming North and Central Asia. • Africa was possibly a continent. • An Arctic continent is supposed to be existed in Nort of Greenland • Brazile, Central africa , Madgascar, India and W. Australia were in connection forming an equatorial continent of great extent ; that is Gondwana-land
  52. 52. All fossils in the Ordovician Diceromyo nia © 2004 Dinorthis © 2003 Platystrophi a acutilirata © 1998
  53. 53. Prasopora falsei © 2006 Rhynchotrema © 2003 Prasopora falsei © 2006
  54. 54. Orthoceras amplicameratum © 2003 Foerstiphy Orthoceras amplicameratum © 2003 llum vacua 1998
  55. 55. Grewingkia canadensis © 2004 Rugose coral © 2004
  56. 56. Eotomaria © 2003 Flexicalymene meeki © 2004
  57. 57. Isoteloides flexus © 2005 Homotelus florencevillensis © 2005
  58. 58. Isotelus maximus © 1906 Xylabion © 2006
  59. 59. Isotelus mafritzae © 2006 Paratrinucleus acervulosus © 2005
  60. 60. The Ordovician Mass Extinction • Fast Facts • -Ordovician period (488- 444 million years ago). - Ordovician extinction (444 million years ago). - Ordovician extinction was second most devastating in earth history. • Geological Setting • The Ordovician period was an era of extensive diversification and expansion of numerous marine clades. Although organisms also present in the Cambrian were numerous in the Ordovician, a variety of new types including cephalopods, corals (including rugose and tabulate forms), bryozoans, crinoids, graptolites, gastropods, and bivalves flourished. Ordovican communities typically displayed a higher ecological complexity than Cambrian communities due to the greater diversity of organisms. However, as in the Cambrian, life in the Ordovician continued to be restricted to the seas
  61. 61. Speculated Causes of the Ordovician Extinction  Glaciation and Sea-Level Lowering Hypothesis • The Ordovician mass extinction has been theorized by paleontologists to be the result of a single event; the glaciation of the continent Gondwana at the end of the period. Evidence for this glaciation event is provided by glacial deposits discovered by geologists in the Saharan Desert. By integrating rock magnetism evidence and the glacial deposit data, paleontologists have proposed a cause for this glaciation. When Gondwana passed over the north pole in the Ordovician, global climatic cooling occured to such a degree that there was global large-scale continental resulting in widespread glaciation. This glaciation event also caused a lowering of sea level worldwide as large amounts of water became tied up in ice sheets. A combination of this lowering of sea-level, reducing ecospace on continental shelves, in conjunction with the cooling caused by the glaciation itself are likely driving agents for the Ordovician mass extinction