Early Paleozoic

Periods of the Early Paleozoic ► Cambrian: mya ► Ordovician: mya ► Silurian: mya

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

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 marine) ► Evaporites (equatorial dry conditions) ► Lithic Sandstone and greywacke (mountain uplift) ► Arkose (arid conditions) ► 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

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

Cratonic Sequence of Paleozoic ► : Late Proterozoic to early Ordovician ► Sauk Sequence: Late Proterozoic to early Ordovician ► : Early Ordovician to early Devonian ► Tippecanoe Sequence: Early Ordovician to early Devonian ► : Early Devonian to end of Mississippian ► Kaskakia Sequence: Early Devonian to end of Mississippian ► : Pennsylvanian to Early Jurassic ► 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)

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

Arches and Basins

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, reef-fringed basins develop in Great Lake region

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 65 o latitude  Reefs, evaporates, eolian sands below 40 o latitude

Late Paleozoic ► Devonian ( m.y.a.) ► Mississippian ( m.y.a.) ► Pennsylvanian ( m.y.a.) ► Permian ( 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

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 40 o of equator ► Reduced CO 2 in late Paleozoic causes cooling and then late Paleozoic Ice Age

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