505-438 my
Paleogeography & Tectonics
High sea level. Cratons flooded.
North America covered by shallow epicontinental seas.
Several sea level fluctuations (trans & regr)
Baltica nears Laurentia causing Taconic Orogeny & volcanism.
Collapse of Cambro-Ordovician carbonate platform and
deposition of clastic wedge in eastern North America.
First "tectonic cycle" in Appalachians:
- SS molasse (red SS)
- SH flysch (black shale & turbidites)
- LS shallow shelf deposits (carb. platform)
Evidence for volcanism found in GA - layer of volcanic ash -
bentonite - interbedded with carbonates; has caused
silicification of underlying beds (green chert)
Paleoclimatology
Evidence for climatic cooling -
major glaciation in Gondwanaland near end of Ord.
glacial depo. in NW Africa
rapid sea level drop in Late Ord
Life
- Early Ord - a time of adaptive radiation of many faunal
groups, following the mass extinction of trilobites and
nautiloids at end of Cambrian.
150 families -> 400 families
- Representative fauna:
brachiopods, rugose & tabulate corals, bryozoans,
crinoids, conodont animals, JAWLESS fishes
- Most marine organisms were epifaunal; few infaunal
- Predators
Evolution of increasing effective predators.
Major predators were invertebrates
- Decline of stromatolites
- New kinds of reefs appeared
bryozoans, stromatoporoids, tabulate corals
- Plants probably colonized the land; land plants were
well established by the Silurian.
- Mass extinctions of tropical marine faunas at end of
Ord.
100 families extinct
more than half of the bryozoan and brachiopod species
died out
Causes?
- climatic cooling
- major glaciation
- sea level drop
- Iapetus Ocean (proto-Atlantic) closed, eliminating
habitats
- Cambro-Ord platform collapsed
- Taconic Orogeny
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This page created by Pamela J. W. Gore
DeKalb College, Clarkston, GA
October 1995.
Last modified November 12, 1996