GEOL 102 Historical Geology

Spring Semester 2012
The Early Paleozoic I: Cambrian Geology

So now we are at the Phanerozoic:

Starting with the Paleozoic:

Phanerozoic Eon: 542 - 0 Ma

Base of Cambrian (and thus of the Paleozoic, and Phanerozoic):

The "Long Fuse" of the Cambrian Explosion:

More on Cambrian life later.

The Cambrian Substrate Revolution
Evidence for microbial matgrounds in shallow marine sediments (siliciclastic & carbonate) during Neoproterozoic:

During Cambrian, rise of some bioturbators, with limited vertical mining abilities.

Presence of surviving mat scratchers (diverse ancestral mollusks, esp. diverse monoplacophorans and polyplacophorans), and some probable mat-sticking echinoderms (helioplacoids). As rise of deeper burrowers and grazing increases in late Cambrian, increasingly Phanerozoic-style substrates:

Paleogeography and Tectonics of the Cambrian
Pannotia (supercontinent) breaks apart at or near the base of the Cambrian. Breaks up into:

Global (eustatic) transgressions in Middle & Late Cambrian:

Paleogeography and Geology of the Ordovician:
Gondwana moves poleward

During Late Ordovician, major (but brief) glaciations.

In eastern Laurentia, Early & Middle Ordovician huge stable carbonate platform (continuation of Cambrian).

During Middle-Late Ordovician, the Taconic Orogeny (first of the Appalachian orogenies):

Collision and suturing between Avalonia and Laurentia possible in northern part of Appalachian region; however, still seem to have been separate further south.

Glaciers at end of Ordovician produce pulses of extinction.

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Last modified: 9 January 2012