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Geologic History of Alabama's River Systems. (Abstracts).

GEOLOGIC HISTORY OF ALABAMA'S RIVER SYSTEMS.

Andrew K. Rindsberg, Geological Survey of Alabama.

Alabama's rivers have a high degree of endermism that can be attributed in part to long separation of drainage basins. However, the riverine faunas are also interrelated in ways that suggest that the river systems have been connected at times.

The geologic record sheds some light on this problem. Based on stratigraphy and geomorpliology, the upland basins of the Chattalnoochee, Coosa, Cahaba, Black Warrior, and middle Tennessee Rivers were already established by the Late Cretaceous sea-level highstand. As the shore receded, rivers extended themselves across the Coastal Plain arid some may have interconnected inn the Paleocene and Eocene before the next extreme highstand in the Oligocene. The Oligocene highstand isolated the upland basins from one another and greatly reduced the river systems' area, presumably leading to high rates of extinction and speciation. During the Tertiary, upland basins were probably' repeatedly filled with allurvium arid then exhumed, shifting between soft arid hard bottoms. Only a few streams at high elevations, such as Talladega Creek, could nave maintained relatively corrstant conditions.

Unusually extensive alluviation during the Miocene may nave allowed rivers to wander out of their usual basins before becoming reestablished; notably, the Tennessee River may have drained across tire Warrior basin into Mississippi. During the Pliocene, the Alabama arid Tombigbee Rivers greatly expanded their drainage basins. When the Alabama captured the Cahaba and Coosa Rivers, all these diverse faunas intermingled -- arid simultaneously the lower courses of the captured rivers iii southeastern Alabama were isolated. During the Pleistocene, the on major rivers eroded downward about 200 to 250 feet, making the Black Belt into a trough and scooping out the unpland basins once again.
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Publication:Journal of the Alabama Academy of Science
Article Type:Author Abstract
Geographic Code:1U6AL
Date:Apr 1, 2002
Words:285
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