The Geology of the Paleozoic Era

The Geology of the
Paleozoic Era
The Paleozoic Era.
• Geologic periods in Paleozoic record 7% of
Earth’s history
• Cambrian, Ordovician, Silurian, Devonian
Carboniferous (Miss., Penn.) Permian
• Boundaries in the major divisions originally
defined by changes in the fossil record
• Start of the Paleozoic used to be defined by
appearance of first easily visible fossils; later
lowered to include small shelly fauna; then
lowered further to first appearance of complex
branching trace fossils.
Base of the Cambrian system
Trace fossil Phycodes pedum
New modes of locomotion
Welsh Lower Paleozoic
Prof Adam Sedgwick (Cambridge) studied the
Cambrian (including the Ordovician) based on
superposition and structural geology.
Roderick Murchison described and mapped the Silurian
based on fossils. Together they defined the Devonian
System in Devon and Cornwall.
Murchison established the Permian in Russian.
Charles Lapworth separated the Ordovician.
Review: Origin of names
Paleozoic Overview
• Global tectonic theme of the Paleozoic assembly of the supercontinent, Pangaea.
• Deposition due to transgressions (and
disconformities due regressions) of shallow
continental (epeiric) seas. Interiors of continents
were frequently flooded.
• Formation of mountain belts at edges
– tectonic activities associated with the assembly of
Pangaea.
Transgression and Regressions
Extinctions:
Paleozoic Era key events
http://www.fmnh.helsinki.fi/users/haaramo/Meteor_Impacts/Middle_Paleozoic_impacts.htm
Rifting raises water, moves plates, which later collide.
Assembly of
Pangea
Gondwana/Laurasia
Catskill Clastic Wedge
Continues subd Iapetus South docks rest Avalonia
Old Red SS
Iapetus floor subducted Scotl Scan NE Can
Lauentia and Baltica collide - Laurasia
Avalonia collides with Laurentia
Paleozoic Global Geology
• Six major Paleozoic continents are
recognized after Rodinia breakup
• Gondwana - S. continents, India
• Laurentia - North America, Greenland,
part Gr. Britain
• Baltica – Northern Europe
• Siberia – Most of Northern Asia
• Kazakhstania – part Central Asia
• China - All of SE Asia and SE China
Paleogeographic
Reconstructions and Maps
• Geologists want to create maps of the
Earth as it was in the past,
• correctly position the continents for
different time periods, and
• reconstruct geography on the continents.
What data are used to do this as
accurately as possible?
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Paleomagnetism Latitude
Biogeography - Distribution of flora and fauna.
Climatology - Climate sensitive sediments
Tectonic Patterns – continuation of mountains
Can’t use Magnetic Stripes on ocean floorMesozoic and later
Global paleogeography for the
Cambrian period
All six continents occur at low paleolatitudes
Ocean waters circulate freely/ poles appear ice-free
Epeiric seas cover much of continents except Gondwana
Highlands in N Gondwana, Eastern Siberia, Central Kazakhistan
Six major Paleozoic continents are recognized after Rodinia breakup
Laurentia - North America, Greenland, Scotland Rotated 90o
Baltica - Russia (W of Urals), Scandinavia
Siberia - Russia (E of Urals), Part Asia
Kazakhstania - Kazakhstan
China - All of SE Asia and SE China
Gondwana - S. continents, India
Ordovician - Silurian
SILURIAN
– Silurian collision of Baltica/Laurentia
Caledonian Orogeny, suturing forms Laurasia
----------------------------------ORDOVICIAN
– Ordovician Gondwana moved 40o S to a South Pole
location (Glaciers formed, we find L. Ord. tillites)
– Baltica moved S, then N
– Microcontinent & Island Arcs collided with Laurentia
(led to Taconic Orogeny) narrowing Iapetus
How do we know?
L. Ordovician biogeography of Carolinites genacinaca
Confirms paleomagnetic latitudes
From McCormick & Fortey 1999.
J. Paleontol. 73(2):202-18.)
Trilobite Paleogeography
Global paleogeography
Mid Ordovician to Silurian
Siberia moved from equatorial
to northern temperate latitudes
Small piece of
Avalonia hits in
Ordovician
Baltica moved S, then N
and collided with Laurentia, rotated 30o
Remember Hawaiians
And Emperor Chain
Evidence of changing directions
Varying rifting pushes
Gondwana moved 40o S to a
South Pole location (Late Ord. tillites)
http://www.geodynamics.no/Platemotions/500-400
M. Ordovician
http://www.gl.rhbnc.ac.uk/seasia/Bio
eog_pdfs/Fortey_Cocks.pdf
Saucrorthis
Mostly distinct faunas
Continents were not close
Devonian
– Acadian Orogeny in the Appalachian
– Other orogenies: Antler (Cordillera) and
Ellesmere (north margin of Laurentia)
– Gondwana moves to higher southern
latitudes. All other continents at low northern
latitudes.
Paleogeography Early Devonian
Continued collision of Baltica/Laurentia formed Laurasia, closed Iapetus Ocean
Caledonian Orogeny in B/L finishes E. Dev
Acadian Orogeny in the Appalachians
folds older rocks M. Dev.
Other orogenies: Antler (Cordillera) and Ellesmere (north margin of Laurentia)
Gondwana moves to higher southern latitudes.
All other continents at low northern latitudes.
Oklahoma and Morocco Trilobites from the Devonian
Looks like Oklahoma was close to Morocco
Dalmanitidae
Reedops
Devonian Faunal Similarities
Dicranurus
Final Assembly of Pangea
• Laurasia collides with Gondwana to form
Hercynian Mts. Late Paleozoic forms Europe
• Pennsylvanian – Siberia collided with
Kazakhstania, forming Altai Mts.
• Permian – Kazakhstania collided with Baltica,
forming the Urals
• Single continent surrounded by Panthalassa
Ocean w Tethys Sea
Gondwana – Laurasia collision
Hercynian orogeny
North and South Europe suture
Hercynian Orogeny continuous w Allegheny
Orogeny about 300 mya
Final Assembly of Pangaea
• After the suturing of Gondwana and Laurasia
(includes Hercynian and Allegheny Orogenies),
• Then:
• Siberia collided with Kazakhstania in the
Pennsylvanian, forming the Altai Mountains.
• Kazakhstania collided with Baltica in the
Permian, forming the Ural Mountains.
Paleogeography Late Permian
Allegheny Orogeny
Hercynian
N Eur-S Eur
Next let’s look closer at the Orogenies
Paleozoic Era key events
Rifting raises water, moves plates, which later collide.
Assembly of
Pangea
Gondwana/Laurasia
Catskill Clastic Wedge
Continues subd Iapetus South docks rest Avalonia
Old Red SS
Iapetus floor subducted Scotl Scan NE Can
Lauentia and Baltica collide - Laurasia
Avalonia collides with Laurentia
Tectonics Paleozoic North America
• In the Cambrian, several small terranes
lay to the south of Laurentia as it
separated from Baltica. The shores were
passive margins.
• In the Ordovician, about 500 mya, the
direction of plate motion reversed and
Iapetus began to close.
Global paleogeography for the
Cambrian period
Terranes
The Taconic orogeny
Rodinia breaking up
Avalonia Terrane E. Cambrian
Plates reverse, in E. Ordovician
Laurentia moves toward Avalonia
Africa moves toward both
Taconic orogeny (cont)
Mid – L. Ordovician, N.Avalonia
and an island arc dock with
Laurentia, beginning the
Appalachians
Rocks thrust up over margin of Laurentia
Interior of Laurentia, Ord.-Silurian
• Inland, the Taconic collisions caused the
crust to be warped down, forming the
Appalachian FORELAND BASIN
• Deep water sediments were deposited in
the basin, until sediments eroded from the
Taconic mountains filled the basin, and
shallow water deposits prevailed.
• The Queenston Clastic Wedge.
Cambrian paleogeography
Pre –collisions
Note equator
Paleogeography N. Am. M Ord-Sil.
Post collisions
Barrier Reefs Highstand
Evaporites Lowstand
Queenston Clastic Wedge
Queenston clastic wedge
(Martinsburg Shale)
Hardyston Fm
downfolded
(Allentown Dm., Jacksonburg Ls.)
The Caledonian Orogeny
• Baltica sutured onto Laurentia
– Mountains - Nova Scotia to Scandinavia
– Erosion resulted clastic wedge
– Devonian Old Red Sandstone
• Result called Laurasia
Late Silurian - Early Devonian
Caledonian Orogeny-Laurasia forms
Caledonian Orogeny
To our North
The Acadian Orogeny
• Continued subduction of Iapetus ocean floor
in Devonian
• Additional parts of Avalonia docked with Laurentia
– Re-folding of Old Mountains – Virginia to Maritimes
– Old rocks even more folded and metamorphosed
– Erosion resulted Catskill clastic wedge
– Facies change in foreland basin – shallow marine to
streams in Middle Devonian as basin fills
– Field trip Marcellus to Mahantango Centerfield Reef
– Catskill delta as push stopped and basin filled
Early - Mid Devonian
Acadian Orogeny-Laurasia forms
Acadian Orogeny
Southern Avalonia into Laurasia
BIG Collision with Gondwana
The Allegheny Orogeny
• Initial contact Late Mississippian
• Northwest Africa collided
• Folding of Pennsylvanian rocks proves
long duration
• Deformation much more extensive than
the Taconic or Acadian – New York to
Alabama
Transgression and Regressions
Paleozoic Era key events
Rifting raises water, moves plates, which later collide and fold. Folding makes deep basin. If fold basin sediments, uplift.
Assembly of
Pangea
Low
High
ABS: Sea level rise (cyclic) due Gondwana glaciation Penn-Pm regression due
slowdown spreading, assembly of Pangaea, drained continent L Pm
KS: filling in of the Appalachian foreland basin by Late Devonian time
TC: glacial melting and accelerated sea-floor spreading
Sauk: High rates of sea-floor spreading
Time-transgressive Cambrian
rocks Grand Canyon
Sauk Sequence
WEST
Transgression
Middle
Cambrian
http://www.geo-tools.com/trilobites.htm
Lower
Cambrian
http://www.wmrs.edu/projects/trilobites/images/trilo7-2.jpg
Note how western BAS is older than eastern BAS
EAST
Climate/Sedimentation
Paleozoic Era key events
Rifting raises water, moves plates, which later collide and fold. Folding makes deep basin. If fold basin sediments, uplift.
Assembly of
Pangea
Next: Paleozoic Climates
•
Paleozoic mostly warm, but two glacial times,
Ordovician and Pennsylvanian to Late
Permian.
•
Cool Middle Ordovician
– CO2 tied up in carbonates – no greenhouse
– Extensive Gondwana tillites and
striations
– Sea level retreats as glacier holds
water
Late Paleozoic Climates
(1) Cool Pennsylvanian – M Permian
– CO2 tied up in carbonates
– Extensive Gondwana tillites and
striations – sea-level fluctuations due
glacial (slow regression) and
interglacial (fast melt) “cyclothems”
– Generated Coal deposits, carbon reservoirs,
low CO2
Pennsylvanian Glacier -Gondwana
Sea-level falls/rises as glaciers grow/melt
Pennsylvanian Cyclothems
Rapid transgressions
cover swamp as ice
melts
Coal Swamp
swamp
estuary
Slow regression as
ice sheet grows
Coal formation Pennsylvania cyclothems
Highland
source to
east
Pennsylvanian-age coal deposits
Late Paleozoic Climates - 2
(2) The Late Permian WARM
• Pangaea was ice-free
• Warm equatorial waters from the Panthalassa
Ocean reached both poles.
• No glaciers = no coal (need rapid transgression)
• The Gondwana landmass had drifted north into
warmer climates.
• reduced coal formation caused carbon dioxide
levels to rise
• Greenhouse effect
L. Permian Pangaea
Ice-free, dry interiors, no coal
Much of land +/- 30 degrees
Pangaea is assembled, sea-level low
Hot, dry climate
Note evaporites
PERMIAN N. America
• Inland sea limited to w Texas & s NM
• Extensive evaporite deposits KS – OK
• Redbeds over interior – strong seasons