Transcript The Late Paleozoic Era

The Late Paleozoic Era
Geology 103
Sea level changes
• Kaskasia transgression
starts in Devonian,
continues to the end of
the Mississippian
• Absaroka transgression
begins in Pennsylvanian,
continues to Triassic
Late Paleozoic plate configuration
• Basically, Pangea is assembling
• Gondwana still exists (over South Pole for most of
this) and Laurentia is equatorial
End Paleozoic plate configuration
• At end of Paleozoic, Pangea is complete
• Tethys ocean begins opening in the east
Acadian orogeny continues through Devonian
• To the north, Laurentia
+ Baltica = Laurasia
• To the south, an island
continent called
Avalonia accretes onto
southern Laurentia
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
Roots of mountain ranges
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)
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)
Western North America has been quiet
since the Antler orogeny, but in Permian,
Sonoma orogeny begins
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
Mississippian in Laurentia was
characterized by extensive limestones
Crinoids (modern sea lilies), blastoids, bryozoans and fusilinid forams
Reconstruction of Mississippian sea floor
Tetrapod evolution
• Some fish had developed lungs
• Changes to fin structure led to feet – land animal
• Transitional form – Tiktaalik (375 my)
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
Tetrapod cladogram
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)
Massive CO2 drop may have removed some
greenhouse warming, resulting in midCarboniferous ice age
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
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
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”)
Almost for naught – Permian extinction which
occurs in less than 1 million years
Causes of P/T extinction – climate change
• Supercontinent interior generates extremes in
temperature – 50°C average temperature in the interior
• Habitable areas reduced
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
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
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
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