The Late Paleozoic Era

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The Late Paleozoic Era

• Geology 103

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Sea level changes

• Kaskasia transgression starts in Devonian,
  continues to the end of the Mississippian
• Absaroka transgression begins in Pennsylvanian,
  continues to Triassic

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Late Paleozoic plate configuration

• Basically, Pangea is assembling
• Gondwana still exists (over South Pole for most
  of this) and Laurentia is equatorial

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End Paleozoic plate configuration

• At end of Paleozoic, Pangea is complete
• Tethys ocean begins opening in the east

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Acadian orogeny continues through Devonian

• To the north, Laurentia Baltica Laurasia
• To the south, an island continent called Avalonia
  accretes onto southern Laurentia

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Catskill clastic wedge and some crystalline rocks
are all that remain

• When the 4000 meter mountains are eroded away,
  all that remains are
• their crystalline roots, both metamorphic and
  intrusive igneous
• Their erosion products in the clastic wedge

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Roots of mountain ranges
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Alleghenian/Ouchitan orogeny Miss. - Permian

• Alleghenian orogeny is a result of a collision
  between parts of northern Laurasia and Gondwana,
  which spread southward to present-day Oklahoma,
  Texas, Louisiana, Venezuela (Ouchitan orogeny)

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Ancestral Rockies orogeny

• Around the same time (Miss. Permian),
  compressive forces in the middle of Laurasia
  created a series of ranges and basins (the
  ancestral Rockies)
• Many basins become oil-producing regions (Big
  Horn Basin), not just in North America (Perm
  Basin, Russia)

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Western North America has been quiet since the
Antler orogeny, but in Permian, Sonoma orogeny
begins
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Late Paleozoic life diversifies but is marked by
two extinctions

• End of Mississippian
• End of Permian (greatest of all extinctions)
  90 of marine species and 70 of land species go
  extinct

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Mississippian in Laurentia was characterized by
extensive limestones
Crinoids (modern sea lilies), blastoids,
bryozoans and fusilinid forams
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Reconstruction of Mississippian sea floor
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Tetrapod evolution

• Some fish had developed lungs
• Changes to fin structure led to feet land
  animal
• Transitional form Tiktaalik (375 my)

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Amniote egg evolution

• Amnion membrane around fetus
• Group within tetrapods that produce eggs that are
  surrounded by membrane(s)
• First of this type around 340 my
• Synapsids (which lead to mammals) and sauropsids
  are part of these

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Tetrapod cladogram
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Pennsylvanian in Laurentia was a time of
extensive coal deposition

• To make so much coal, lots of carbon dioxide was
  scrubbed from the air
• Atmospheric CO2 drops to a tenth of previous
  (about modern day values)

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Massive CO2 drop may have removed some greenhouse
warming, resulting in mid-Carboniferous ice age
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Deposition of cyclothems

• Cyclic sedimentary package of rocks, ranging
  from coal to limestone
• Each cycle represents about 400,000 yr
• The standard interpretation is that there are
  small transgressions and regressions at coastal
  regions where there are swamps

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Permian in Laurentia was a time of extensive
deserts

• Pangean continental interiors were dry, so
  extensive deserts and dunefields formed
• Result are arenites with huge (meter-scale)
  cross-beds

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Therapsids, ancestors of mammals

• Division of synapsids
• Still are reptiles but have some mammalian
  characteristics like hair, lactation and erect
  posture
• apsid arch, typically over a hole in the
  skull (fenstra)

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Almost for naught Permian extinction which
occurs in less than 1 million years
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Causes of P/T extinction climate change

• Supercontinent interior generates extremes in
  temperature 50C average temperature in the
  interior
• Habitable areas reduced

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Causes of P/T extinction climate change

• At Hallett Cove, South Australia, among other
  sites, extensive glacial striations exist in
  exposed bedrock of end Permian times
• Worldwide glaciation was already occuring
  regularly during Permian
• Regressions caused by glaciations remove habit on
  continental shelf

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Causes of P/T extinction massive vulcanism

• Siberian traps are a region of huge outpourings
  of basaltic lava around the end of the Permian
• Increase CO2 in atmosphere, as well as dust

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How does a massive volcanic eruption cause enough
climate change for a mass extinction?

• Initial temperature rise due to eruption CO2
  increase warms oceans enough to exsolve trapped
  methane from ocean floor, which increases the
  warming

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Causes of P/T extinction - impacts

• Potential impact sites of the right timing in
  Australia and Antarctica
• Identified through presence of shocked quartz and
  stishovite, a high pressure form of quartz