Paleogeography of the Late Paleozoic World

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Paleogeography of the Late Paleozoic World
186-233A Earth Life History (Fall 2001)
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Recommended reading STANLEY Earth System
History Chapter 15, pp. 414-431.
Keywords Carboniferous (Mississipian,
Pennsylvanian) and Permian periods, coal
cyclothems, concretions, Ancestral Rocky
Mountains, seasonal climate,
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In Europe, the Carboniferous system is split in
Early, Middle and Late intervals. (The right hand
side names as stages defined on the basis of
biozones.
In North America, the Carboniferous system is
split in the Mississipian and Pennsylvanian
periods.
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The Mississipian strata are separated from the
younger Pennsylvanian strata by a 4-million year
gap. This discomformity is an interval of
non-deposition. Bedding is parallel in strata
below and above it. Many genera of crinoids and
ammonoids disappear at that level.
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A disconformity separates two sequences that are
flat-lying (unlike an angular unconformity) but
shows evidence of erosion at the top of the older
formation.
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In Pennsylvanian (or Carboniferous) strata, coal
beds occur between other rock types. The
different rock types form remarkably repetitive
cycles at any one locality.
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Sea level fluctuations caused these cycles
Predominantly marine section covers the coal.
Coal covers a predominantly non-marine section
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Coal forms from plant remains accumulating in
swamps found between channels of river deltas.
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Part of the non-marine sequence within cyclothems
is due to the movement of delta lobes, flooding
the swamps with coarser sediment (sands) carried
by the meandering river.
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Ice caps grew and shrank repeatedly... Sea level
changes caused the cyclothems.
During the Carboniferous,Gondwanaland joins
Euramerica.
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When glaciers shrank, during the Upper
Carboniferous, lycopods and seed ferns were
replaced by spore ferns, which were better
adapted to moister conditions.
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Joggins, Nova Scotia.
Cliffs are washed by the tides of the Bay of
Fundy. New material is constantly eroded and
exposed.
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Joggins has also yielded fossils of - insects -
plant fossils - footprints
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Dendrerpeton skull, Joggins (NS). Its limbs and
skull structure suggest a more terrestrial than
most amphibians.
Calamites trunk and its modern relative, a
horsetail.
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This tree trunk was buried in sediment on the
floodplain. Some tree trunks contain complete
skeletons of small animals, like this Hylonomous.
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A 2-meter long myriapod (as drawn by Dawson,
above), left trackways (right) at Joggins. The
same arthropod is known from other localities.
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Spectacular fossils of Carboniferous age are also
found south of Chicago, Illinois, in an area
named from a local river, Mazon Creek. By 1979,
320 species had been described from the deposit.
Most Mazon creek fossils can be assigned to
either a marine fauna or a freshwater-terrestrial
fauna.
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myriapod
Tully monster
insect
The best fossils are found by cracking open
siderite (FeCO3) concretions that stick out from
the weathered siltstone.
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Coal balls are rounded masses of limestone or
siderite. These concretions can form in coal
beds during early burial. A carbonate mineral
(CaCO3) is dissolved and redistributed within the
sedimentary layers. The carbonate mineral
reprecipitates as tiny crystals around an intact,
dead animal. This produces a hard envelope which
preserves delicate fossils from being crushed
during deeper burial.
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The reassembly of continents into the
supercontinent Pangea continued throughout the
late Paleozoic.
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Uplift and downfaulting in southwestern U.S.
along deep, nearly vertical faults. This suggests
that the crust was being stretched rather than
compressed. The exact cause is unclear...
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above ground underground
Carlsbad caversn
The Permian Reef complex
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reef model
encrusting algae under microscope
fusulinid foraminifer under microscope (below)
reef rock with sponge
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High sea level reef growth. Low sea level
clastics eroded from land are deposited.
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Limestone layers become interbedded with red
sandstones during periods of lower sealevel.
Sandstones fill channels dug in the basinal shale.
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Top evaporites were deposited in the shallow
lagoon. Dark layers are CaCO3 and the white
layers are gypsum (CaSO4 . 2H2O). Thin varves
(layers) correspond to yearly cycles of wet and
dry seasons. Bottom Gypsum crystal in the
basinal shale.
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The magnitude and suddenness of the Permian
extinction are unique in the fossil
record. Tectonic movements are slow... The drier
climates of Pangea and the glaciations did not
develop particularly abruptly. What other
mechanisms could have dealt a fatal blow to
marine communities that were already under
significant stress?
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Flood basalts are caused by mantle plumes
(right). Similar episodes occurred several
times through Earths history.
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On this map of igneous provinces of the world,
interpreted as mantle plume events, the late
Permian Siberian Traps stand out by their
extent.
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Complete late Permian sequences are rare.
Meishan, China, contains ash beds, critical for
dating the two pulses of extinction that mark the
late Permian.