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Early Paleozoic

Early Paleozoic. Periods of the Early Paleozoic. Cambrian: 570-505 mya Ordovician: 505-438 mya Silurian: 438-408 mya. Overview of Paleozoic. Broad Sequence of Events Gradual Marine invasion of low continents Wide epeiric (shallow) seas; moderated climate

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Early Paleozoic

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  1. Early Paleozoic

  2. Periods of the Early Paleozoic • Cambrian: 570-505 mya • Ordovician: 505-438 mya • Silurian: 438-408 mya

  3. Overview of Paleozoic • Broad Sequence of Events • Gradual Marine invasion of low continents • Wide epeiric (shallow) seas; moderated climate • Wide shallow habitats for marine organisms • Epeiric seas retreated; instability occurred • Thick sedimentary layers and Volcanic deposits developed • Collisional Mountain ranges built

  4. Plate Tectonic Events • Break-up of Rodinia • Oceanic closing and orogeny to form Pangaea • Taconic orogeny • Acadia orogeny • Alleghenian orogeny • Caledonian Orogeny • Hercynian Orogeny

  5. Clues to Paleogeography • Paleomagnetic evidence • Lithologic evidence • Limestone (shallow marine) • Evaporites (equatorial dry conditions) • Lithic Sandstone and greywacke (mountain uplift) • Arkose (arid conditions) • Tillites • Quartz sandstone • Shales

  6. Laurentia (N. America) and Gondwanaland (first stage of Pangaea ) • Gondwanaland • formed in southern hemisphere • consists of S. America, Africa, and other shields • Drifter south to polar position • Laurentia • Lay on equator • rotated counter clockwise

  7. Continental framework • Stable interior • Arches • Synclines • Basins • Domes • Orogenic Belts • Cordilleran Mtn • Franklin Mtn • Appalachian Mtn • Caledonian mnt

  8. Paleogeography of Laurentia • Equator: North-central Mexico to Ellsmere Island, Canada • Vast epeiric Sea (30o Latitude; vast carbonate deposits) • Vast lowlands of Canada Shield were exposed (desert) • Volcanic Mnts: Texas and New England

  9. Seaways • Appalachians (on east) • Cordilleran (on west) • Franklinian (on north) • Caledonian (on northwest) • Extensive Sediment belts • Shales in seaways • limestone in empieric seas • Quartz sand on shoreline and deserts

  10. Base of Cambrian • Sedgwick’s original base (1835) • At top of nonconformity in Wales • At the first trilobite bearing fossiliferous beds • Later dated at 560 my • New concept: Tommotian Stage (1970) • Base of Cambrian set at 570 my • New stage included fossiliferous rocks above Vendian and some fossiliferous rocks • Fossils in new stage: porifera, brachiopods, and organisms of unknown affinity

  11. Cratonic Sequence of Paleozoic • Sauk Sequence: Late Proterozoic to early Ordovician • Tippecanoe Sequence: Early Ordovician to early Devonian • Kaskakia Sequence: Early Devonian to end of Mississippian • Absaroka Sequence: Pennsylvanian to Early Jurassic

  12. Early Paleozoic History • Synopsis of Sauk Transgression • Canadian Shield eroded for 50 my prior to transgression • Gradual transgression covered shield • Transcontinental Arch (highlands) became island chain in shallow epeiric sea • Transcontinental Arch: Ontario to Mexico, parallel to Cambrian equator • As a Result: • Late Cambrian seas: MT to NY • Cordilleran deposits of Grand Canyon • Tapeat Sandstone (oldest) • Bright Angel Shale • Mauv Limestone (youngest)

  13. Time and Facies (Slight tangent) • Bright Angel Shale: good example of temporal transgression of facies • Early Cambrian (CA) • Middle Cambrian (AZ)

  14. Arches and Basins

  15. Back to the Sauk Sequence • By the early Ordovician sea regresses and deposition ends • Vast continental-scale uncomformity • Karst topography on carbonates rocks

  16. Tippecanoe Sequence • Massive unconformity separates the Tippecanoe from the Sauk Sequence • Known for: • the “Super Mature” Sandstone, St. Peter Sandstone • What could “Super Mature” mean? • Carbonate deposits contain abundant marine fauna

  17. Fauna found in Tippecanoe • Shallow Marine limestones with vast fauna • Brachiopods • Bryozoans • Echinoderms • Mollusks • Corals • Algae

  18. Close of the Tippecanoe • Landlocked, reef-fringed basins develop in Great Lake region

  19. Evaporite region • In some areas evaporites accumulated to 750 meters • If this occurred due to evaporation of a single body of water, the water would have to have been ~1000 kilometers deep Barred Basin

  20. Cordilleran Region History • Sauk Interval • Passive Margin on opening ocean; deep marine basin on west • Western ocean opened; block rotated out; included Siberian region of Asian continent • Arms of rift filled with thick sediments • Belt supergroup (MT, ID, BC) • Uinta Series (UT) • Pahrump Series (CA) • Canadian Rockies (BC, Alberta)

  21. Tippecanoe Interval • Conversion to active margin with subduction (Wilson Cycle) • Volcanic Chain formed along western trench • Trench deposits; greywacke and volcanics • Western ocean deposits: Siliceous black shales and bedded cherts with graptolites (graptolite facies) • East of subduction zone: shelly facies- deposited in back arch basins (fossiliferous carbonates)

  22. Appalachian History • Appalachian Trough: Deformed three times during Paleozoic • Subdivisions of trough: • Eastern sediment belt: greywacke, volcanic siliceous shale • Western sediment belt: Shale, sandstone, limestone • Physiographic region of today • Eastern belt: Blue Ridge and Piedmont • Western Belt: Valley and Ridge and Plateau

  23. Sauk Interval • Trough was a passive margin on opening ocean • Shelf sediments: sandstone and limestone • Oceanic sediments: shales • Transgression spread deposits westward across craton; thick carbonates formed on subsiding shelf • Abrupt end with onset of subduction and ocean closure during Middle Ordovician

  24. Tippecanoe Interval • Carbonate sedimentation ceased; platform downwarped by subduction • Thick graptolite black shale and shoreline immature sands spread west • Volcanic flows and pyroclastic beds formed when volcanoes emerged on coast • Rapid closing of eastern ocean (Iapetus); coastal and volcanic arc developed • Millerburg Volcanic ash bed formed (454 my; 1-2 m thick)

  25. Taconic Orogeny • Appalachian Mountains built in collision with part of western Europe • Compression folded shelf sediments into mnt and Logan’s Thrust formed (48 km displacement)

  26. Taconic Orogeny

  27. Giant granitic batholiths produced by Taconic melting • Taconic Mountains weathered to form vast sandstones of PA, WY, OH, and NY • Great clastic wedges spread westward (age tracts deformation)

  28. Climates • Transgressions= Mild Climates, windswept low terrains • Regressions and Orogenic Episodes= Harsher more diverse climates; winds diverted by mountains • Earth Rotation was faster (shorter days, greater tidal effects)

  29. Climate • No land Plants • Solar Radiation reflected, not absorbed • Sever temperature differences resulting • End of Late Proterozoic Glacial Cycle: Cool beginning for Early Paleozoic • Melting Polar Caps= Rising sea levels and warming • Equitorial Position= tropical climates for Laurentia, Baltica, and Antarctica • No Ice caps= warm polar seas

  30. Climate • Cross Bedding in Desert Sand Deposits • Shows wind blew NE to SW across eastern

  31. Ordovician • Sea Levels and Biotic Extinctions • African Glaciation lowered sea levels and cooled global temperatures • End-Ordovician extinctions in many families • Bryozoans • Tabulate corals • Brachiopods • Sponges • Nautiloid cephalopods • Crinoids

  32. Silurian Climate • Temperature Zonation • Glacial deposits above 65o latitude • Reefs, evaporates, eolian sands below 40o latitude

  33. Late Paleozoic • Devonian (480-360 m.y.a.) • Mississippian (360-320 m.y.a.) • Pennsylvanian (320-286 m.y.a.) • Permian (286-245 m.y.a.)

  34. Pangea • During Silurian Iapetus sea closes - joins Baltica and Lauretia (Caledonian Orogeny) • Devonian-Orogeny continues to south forming Laurussia • Pennsylvanian collision joins Gondwanna Land and Laurussia (Hercynian in Europe, the Alleghenian in N. America • By the Late Permian Pangea is complete

  35. Kaskaskia Sequence • Oriskany sandstone- initial transgression • Devonian Clastics- material shed off rising Appalachians • Upper Devonian-Mississippian • Massive marine deposits • Late Mississippian- Regression • Widespread erosion and development of Karst topography

  36. Absaroka Sequence • Yet another transgression • Unique cyclical sediments • Cyclothems • Shale • Limestone • Shale • Limestone • Coal • Caused by either eustatic rise in sea level (Glacial melting) or by subsidence.

  37. Climate • Zonation paralled latitude • Warm to hot within 40o of equator • Reduced CO2 in late Paleozoic causes cooling and then late Paleozoic Ice Age

  38. Mineral Deposits • Fossil Fuels • Coal • Present in all post Devonian rocks • Oil and Gas • Devonian Reefs Alberta, MT, SD • Appalachian basin PA, WV

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