GEOL 102 Historical Geology

Spring Semester 2011
The Late Paleozoic Era I: Carboniferous Geology

Phanerozoic Eon: 542 - 0 Ma

In traditional non-North American geology the (North American) Mississipian and Pennsylvanian Periods were not recognized; the Mississippian Period is thus the same as the traditional European Early Carboniferous Epoch and the Pennsylvanian Period is equivalent to the traditional European Late Carboniferous Epoch. In the latest international time scale, a compromise was reached, and the Mississippian and Pennsylvanian are "sub-periods" of the Carboniferous (each has three Epochs).

Paleogeography and Geology of the Mississippian:
Tabulate-stromatoporoid reefs disappear; related to switch from calcite seas to aragonite seas:

During Mississippian, no reef complexes of significance.

Huge carbonate banks in most shallow seas: crinoid meadows produce limestones whose main clasts are crinoid columnal elements.

Continued decline of CO2 -- sucked up into soils, and eventually coals -- lowers greenhouse effect, start of new series of Gondwanan glaciations. Non-reduced oxygen accumulates in the atmosphere.

During Late Mississippian, the Variscan Orogeny:

End of Mississippian: major regression, associated with mass extinction of some groups of stalked echinoderms and ammonoids.

Paleogeography and Geology of the Pennsylvanian:
Continued decline of CO2 (to just about modern levels!). O2 levels reach their maximum in Earth history (around or above 30%). Since N2 levels (which represent the majority of the atmosphere) would have likely remained constant, total atmospheric density reaches its highest in the age of blue skies (i.e., since the reducing atmosphere was oxidized).

As a consequence of this, forest fires become EXTREMELY easy to trigger. Also, higher O2 levels may have been the reason that very large terrestrial arthropods could live in the Carboniferous.

Continued glaciation in Gondwana: southern continents remain largely emergent.

Continued Collision of Gondwana and Euramerica:

Alleghanian Orogeny produced the direct "ancestor" of the modern Appalachians: the current mountains are the erosional remnants of the fold-and-thrust belt of the Alleghanian Appalachians.

Unusual cratonic deformation in southwestern Laurentia:


Formation of cyclothems

Some minor reefs formed by sponges, bryozoans, and algae.

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Last modified: 14 January 2011