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 ► ► Epeiric seas retreated; instability occurred ► Wide epeiric (shallow) seas; moderated climate Wide shallow habitats for marine organisms Thick sedimentary layers and Volcanic deposits developed Collisional Mountain ranges built Plate Tectonic Events ► ► Break-up of Rodinia Oceanic closing and orogeny to form Pangaea Taconic orogeny Acadia orogeny Alleghenian orogeny Caledonian Orogeny Hercynian Orogeny Clues to Paleogeography ► ► Paleomagnetic evidence Lithologic evidence Limestone Shallow Sea Equatorial Drying conditions ► Evaporites ► Lithic Sandstone and greywacke Mountain Building Arid conditions-deserts ► Arkose ► Tillites ► Quartz sandstone ► Shales ► 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 Continental framework ► Stable interior ► ► ► ► ► Arches Synclines Basins Domes Orogenic Belts ► ► ► ► Cordilleran Mtn Franklin Mtn Appalachian Mtn Caledonian mnt 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 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 ► 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 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) Back to the Sauk Sequence ► By the early Ordovician sea regresses and deposition ends Vast continental-scale uncomformity Karst topography on carbonates rocks 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 Fauna found in Tippecanoe ► Shallow Marine limestones with vast fauna Brachiopods Bryozoans Echinoderms Mollusks Corals Algae Close of the Tippecanoe ► Landlocked, Lake region reef-fringed basins develop in Great 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 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) 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) 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 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 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) 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) Taconic Orogeny ► 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) 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) 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 Climate ► Cross Bedding in Desert Sand Deposits Shows wind blew NE to SW across eastern 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 ► Silurian Climate ► Temperature Zonation Glacial deposits above 65o latitude Reefs, evaporates, eolian sands below 40o latitude 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.) 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 Forming Pangea Pennsylvannian Silurian Mississippian Devonian Permian 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 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. Climate ► Zonation paralled latitude Warm to hot within 40o of equator ► Reduced CO2 in late Paleozoic causes cooling and then late Paleozoic Ice Age Mineral Deposits ► Fossil Fuels Coal ►Present in all post Devonian rocks ► Limestone- used to produce cement’ ► Silica- glass production ► Silver, gold- mountain building events