was Rodinia rifting apart
Early Paleozoic
Cambrian-Silurian
Laurentia
Baltica
Kazakhstania
Siberia
China
Gondwana
Iapetus Ocean open
then closed
RODINIA to PANNOTIA
North America & Europe
Cambrian
to Silurian
Domes and basins
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Vendian to Ordovician
Cratonic sequences
World was undergoing an eustatic
transgression.
This is called the SAUK SEA.
Flooded nearly entire North America ~500
myr ago.
Also, N.A. was on the equator.
What was going on with the diversity of
life?
Sauk sea
Sauk sea
Evidence of ripple marks, oolites, and
stromatolites indicate that the Sauk sea
was probably <200ft.
How do we know this? The photic zone
can be no deeper than 150-200ft in clear
waters.
First Paleozoic transgression (Cambrian).
Early Paleozoic Sediments
Importance of Quartz-rich
sediments
Continent was eroding for 0.5byr.
No definite land fossil records exist older than Late
Ordovician and without plants to hold soil down,
weathering must have been much more widespread
than today.
These sandstones are among the most mature in the
world, they are exceptionally round and are
composed of 99% quartz.
This implies tectonic stability and low
topography.
2
Well sorted sand grains
Where did the Clay go?
Many minerals (NOT QTZ) erode into
various clays.
Transported into deep ocean environments.
Lowest Cambrian based on a
fossil!
Phycodes
A trace fossil.
542 myr ago.
Marine
There wasnt any
life on land yet!
Tippecanoe sequence
Tippecanoe Sea
Second major Paleozoic transgression.
Ordovician through Silurian.
Another period of mature sandstones.
Outcrops can be found in Niagara Falls.
Niagara Falls
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Importance of Evaporites
Formation of evaporites
Within the craton, a different story emerges.
There was low diversity of fauna.
Evidence of evaporite minerals indicate
above normal salinity.
Circulation had become restricted and
produced a high rate of evaporation and
produced a hypersaline environment.
In the Ordovician
TACONIC OROGENY
Clastic limestones began to accumulate
over the sandstone.
This indicates
Beginning in the Ordovician, eastern
margin the became tectonically active.
This is the Taconic orogeny.
Obduction occurred.
Resulted from the closing of the Iapetus ocean
by eastward subduction of a volcanic arc or a
microcontinent.
Zone of ultramac rocks formed along the
Appalachian belt (the suture zone).
Shallow seas
Warm environments
Evidence of agitated, well-oxygenated
clear water with plenty of sunlight for
growth.
N.A. in Ordovician
Taconic orogeny
4
Taconic rocks
OPHIOLITES
Fossils associated with Taconic
Orogeny
Formation of Taconics
Taconic suture
Graptolites
GRAPTOLITES.
Often found in shales.
NOT shallow marine,
but planktic .
Related to Chordates!
5
Ordovician N.A.
Ouachita trough
Located at the southernmost section of
Appalachian chain.
Northernmost Appalachian is in northern
Europe.
Rocks now found in southern margin of
N.A.
Represent volcanic and deep marine
environments.
Silurian N.A.
Shawanagunks
Caledonian Orogeny
Taconic and Acadian histories
A twin of the northern Appalachian-east
Greenland orogeny.
The Caledonian orogeny is Silurian, only
10myr before the Acadian orogeny in N.A.
(which is Devonian).
Structurally the 2 margins of the North
Atlantic Ocean are almost mirror images.
This collision resulted with the closing of
the Iapetus Ocean.
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Early Paleozoic Earth
Early food web
Faster rotation.
Shorter days.
Moon was closer.
Stronger tides.
No vascular plants yet!
Only macrobiotic crusts on land.
More erosion.
Brachiopods
Orthids and Strophomenids
Inarticulate CaPO4
Articulate CaCO3
Bryozoans
Stromatoporoids
not stromatolites!
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Corals
Tabulates and Rugose
receptaculites
Trilobites
Euypterids
Eurypterid
Ostrocods
Early arthropod.
Great index fossil.
NY state fossil!
Found in sandstones and fossil limestones
on continental shelves NOT FOUND
WITH GRAPTOLITES.
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Molluscs
Ordovician top predator
-a cephalopod
-up to 10m in length!
Gastropods
Ordovician Cephalopod
Top predator
-up to 10m in
length!
oldest jawless FISH!
Why so much diversity?
High SL.
O2 increasing
Evolution of predators.
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