Early Paleozoic

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Early Paleozoic
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Periods of the Early Paleozoic

• Cambrian 570-505 mya
• Ordovician 505-438 mya
• Silurian 438-408 mya

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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

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Plate Tectonic Events

• Break-up of Rodinia
• Oceanic closing and orogeny to form Pangaea
• Taconic orogeny
• Acadia orogeny
• Alleghenian orogeny
• Caledonian Orogeny
• Hercynian Orogeny

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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

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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

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Continental framework

• Stable interior
• Arches
• Synclines
• Basins
• Domes
• Orogenic Belts
• Cordilleran Mtn
• Franklin Mtn
• Appalachian Mtn
• Caledonian mnt

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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

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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

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Base of Cambrian

• Sedgwicks 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

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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

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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)

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Time and Facies (Slight tangent)

• Bright Angel Shale good example of temporal
  transgression of facies
• Early Cambrian (CA)
• Middle Cambrian (AZ)

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Arches and Basins
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Back to the Sauk Sequence

• By the early Ordovician sea regresses and
  deposition ends
• Vast continental-scale uncomformity
• Karst topography on carbonates rocks

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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

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Fauna found in Tippecanoe

• Shallow Marine limestones with vast fauna
• Brachiopods
• Bryozoans
• Echinoderms
• Mollusks
• Corals
• Algae

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Close of the Tippecanoe

• Landlocked, reef-fringed basins develop in Great
  Lake region

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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
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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)

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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)

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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

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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

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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)

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Taconic Orogeny

• Appalachian Mountains built in collision with
  part of western Europe
• Compression folded shelf sediments into mnt and
  Logans Thrust formed (48 km displacement)

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Taconic Orogeny
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• 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)

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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)

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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

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Climate

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

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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

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Silurian Climate

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

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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.)

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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

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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

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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.

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Climate

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

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Mineral Deposits

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