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Sedimentological consequences of two floods of extreme magnitude in the late Wisconsinan Wabash Valley

By
Gordon S. Fraser
Gordon S. Fraser
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Ned K. Bleuer
Ned K. Bleuer
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Published:
January 01, 1988

Two floods of extreme magnitude occurred in the Wabash Valley during late Wisconsinan time. The First flood occurred when meltwater that was stored in disintegrating ice to the north was rapidly released into the valley at a point near Delphi Indiana. During the period of gradually increasing flow, a coarsening- and thickening-upward sequence was deposited, and at peak flow, crossbedded cobble gravels accumulated in sets as much as 5 m thick. Trough crossbeds were deposited along narrow reaches of the valley where flow depths and velocities were greatest. Along wider reaches, however, where velocities and depths were less, tabular and convex upward crossbeds were deposited, and in the widest parts of the valley, where the flow was too shallow to maintain equilibrium bedforms, planar-bedded gravels accumulated.

The second flood occurred when a morainal dam was breached and glacial Lake Maumee drained out of the Lake Erie basin and into the valley at Fort Wayne. During initial stages the flood eroded a deep trench in older outwash in the valley, sculpted bedrock outcrops in the valley floor, and carved flutes in uplands where the flow topped valley margins. Deposition occurred during the waning stage, when disorganized cobble gravels in lee-eddy, pendant, and expansion bars were deposited, a train of megaripples was established, and sediments accumulated in the lee of large-scale obstructions on the channel floor.

During both floods, flow strength declined quickly. Waning stage of the first flood is marked only in the uppermost parts of the sequence, where increased sand content, channel-Fills of sand and Fine gravel, and diminished bed-set thickness occur. In the upper parts of the bars deposited during the second flood, sediments fine upward markedly and are organized into well-defined planar beds.

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Contents

GSA Special Papers

Sedimentologic Consequences of Convulsive Geologic Events

H. Edward Clifton
H. Edward Clifton
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Geological Society of America
Volume
229
ISBN print:
9780813722290
Publication date:
January 01, 1988

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