Transcript Early Paleozoic - This Old Earth

Early Paleozoic
Periods of the Early Paleozoic
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Cambrian: 570-505 mya
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Ordovician: 505-438 mya
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Silurian: 438-408 mya
Overview of Paleozoic
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Broad Sequence of Events
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Gradual Marine invasion of low continents
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Wide epeiric (shallow) seas; moderated climate
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Epeiric seas retreated; instability occurred
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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
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Taconic orogeny
Acadia orogeny
Alleghenian orogeny
Caledonian Orogeny
Hercynian Orogeny
Clues to Paleogeography
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Paleomagnetic evidence
Lithologic evidence
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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 )
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Gondwanaland
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formed in southern hemisphere
consists of S. America, Africa, and other shields
Drifter south to polar position
Laurentia
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Lay on equator
rotated counter clockwise
Continental framework
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Stable interior
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Arches
Synclines
Basins
Domes
Orogenic Belts
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Cordilleran Mtn
Franklin Mtn
Appalachian Mtn
Caledonian mnt
Paleogeography of Laurentia
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Equator: North-central Mexico to
Ellsmere Island, Canada
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Vast epeiric Sea (30o Latitude; vast
carbonate deposits)
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Vast lowlands of Canada Shield were
exposed (desert)
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Volcanic Mnts: Texas and New England
Seaways
Appalachians (on east)
► Cordilleran (on west)
► Franklinian (on north)
► Caledonian (on northwest)
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Extensive Sediment belts
Shales in seaways
► limestone in empieric seas
► Quartz sand on shoreline and deserts
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Base of Cambrian
Sedgwick’s original base (1835)
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At top of nonconformity in Wales
At the first trilobite bearing fossiliferous
beds
Later dated at 560 my
New concept: Tommotian Stage
(1970)
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Base of Cambrian set at 570 my
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New stage included fossiliferous
rocks above Vendian and some
fossiliferous rocks
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Fossils in new stage: porifera,
brachiopods, and organisms
of unknown affinity
Cratonic Sequence of
Paleozoic
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Sauk Sequence: Late Proterozoic to early
Ordovician
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Tippecanoe Sequence: Early Ordovician to early
Devonian
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Kaskakia Sequence: Early Devonian to end of
Mississippian
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Absaroka Sequence: Pennsylvanian to Early
Jurassic
Early Paleozoic History
Synopsis of Sauk Transgression
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Canadian Shield eroded for 50 my prior to transgression
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Gradual transgression covered shield
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Transcontinental Arch (highlands) became island chain in
shallow epeiric sea
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Transcontinental Arch: Ontario to Mexico, parallel to Cambrian
equator
As a Result:
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Late Cambrian seas: MT to NY
Cordilleran deposits of Grand Canyon
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Tapeat Sandstone (oldest)
Bright Angel Shale
Mauv Limestone (youngest)
Time and Facies (Slight tangent)
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Bright Angel Shale: good example of temporal
transgression of facies
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Early Cambrian (CA)
Middle Cambrian (AZ)
Arches and Basins
Back to the Sauk Sequence
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By the early Ordovician sea regresses and
deposition ends
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Vast continental-scale uncomformity
Karst topography on carbonates rocks
Tippecanoe Sequence
► Massive
unconformity separates the Tippecanoe
from the Sauk Sequence
 Known for:
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the “Super Mature” Sandstone, St. Peter Sandstone
 What could “Super Mature” mean?
► Carbonate
deposits contain abundant marine fauna
Fauna found in Tippecanoe
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Shallow Marine limestones with vast fauna
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Brachiopods
Bryozoans
Echinoderms
Mollusks
Corals
Algae
Close of the Tippecanoe
► Landlocked,
Lake region
reef-fringed basins develop in Great
Evaporite region
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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
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Passive Margin on opening ocean; deep marine basin on west
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Western ocean opened; block rotated out; included Siberian
region of Asian continent
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Arms of rift filled with thick sediments
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Belt supergroup (MT, ID, BC)
Uinta Series (UT)
Pahrump Series (CA)
Canadian Rockies (BC, Alberta)
Tippecanoe Interval
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Conversion to active margin with subduction (Wilson Cycle)
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Volcanic Chain formed along western trench
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Trench deposits; greywacke and volcanics
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Western ocean deposits: Siliceous black shales and bedded cherts
with graptolites (graptolite facies)
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East of subduction zone: shelly facies- deposited in back arch basins
(fossiliferous carbonates)
Appalachian History
Appalachian Trough: Deformed three times
during Paleozoic
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Subdivisions of trough:
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Eastern sediment belt: greywacke, volcanic siliceous shale
Western sediment belt: Shale, sandstone, limestone
Physiographic region of today
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Eastern belt: Blue Ridge and Piedmont
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Western Belt: Valley and Ridge and Plateau
Sauk Interval
Trough was a passive margin on opening ocean
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Shelf sediments: sandstone and limestone
Oceanic sediments: shales
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Transgression spread deposits westward across craton;
thick carbonates formed on subsiding shelf
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Abrupt end with onset of subduction and ocean closure
during Middle Ordovician
Tippecanoe Interval
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Carbonate sedimentation ceased; platform downwarped by
subduction
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Thick graptolite black shale and shoreline immature sands spread
west
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Volcanic flows and pyroclastic beds formed when volcanoes emerged
on coast
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Rapid closing of eastern ocean (Iapetus); coastal and volcanic
arc developed
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Millerburg Volcanic ash bed formed (454 my; 1-2 m thick)
Taconic Orogeny
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Appalachian Mountains built in collision
with part of western Europe
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Compression folded shelf sediments into
mnt and Logan’s Thrust formed (48 km
displacement)
Taconic Orogeny
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Giant granitic
batholiths produced by
Taconic melting
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Taconic Mountains
weathered to form vast
sandstones of PA, WY,
OH, and NY
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Great clastic wedges
spread westward (age
tracts deformation)
Climates
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Transgressions= Mild Climates, windswept low
terrains
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Regressions and Orogenic Episodes= Harsher
more diverse climates; winds diverted by
mountains
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Earth Rotation was faster (shorter days, greater
tidal effects)
Climate
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No land Plants
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Solar Radiation reflected, not absorbed
Sever temperature differences resulting
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End of Late Proterozoic Glacial Cycle: Cool beginning
for Early Paleozoic
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Melting Polar Caps= Rising sea levels and warming
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Equitorial Position= tropical climates for
Laurentia, Baltica, and Antarctica
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No Ice caps= warm polar seas
Climate
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Cross Bedding in Desert Sand Deposits
 Shows wind blew NE to SW across eastern
Ordovician
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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
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Temperature Zonation
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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
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During Silurian Iapetus sea closes - joins Baltica and
Lauretia (Caledonian Orogeny)
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Devonian-Orogeny continues to south forming Laurussia
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Pennsylvanian collision joins Gondwanna Land and
Laurussia (Hercynian in Europe, the Alleghenian in N.
America
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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 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
 Oil and Gas
►Devonian
Reefs Alberta, MT, SD
►Appalachian basin PA, WV