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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 927

Last Page: 927

Title: Sedimentology of Terrace Deposits at Bend Area of Wabash River: ABSTRACT

Author(s): Gordon S. Fraser, Ned K. Bleuer, David A. Fishbaugh

Article Type: Meeting abstract


Late Pleistocene terrace deposits lining the valley walls of the Wabash River record the change in fluvial regime imposed on the river by the advance and disintegration of the Trafalgar (East White Sublobe) ice sheet.

In the lower part of the terraces, sediments accumulated in a shallow braided stream environment where fluctuating flow was controlled by storms and by diurnal and seasonal melt cycles. The sediments consists of: (1) horizontally bedded cobble gravels deposited as longitudinal bars and channel lags; (2) planar cross-bedded pebble gravels that accumulated as transverse bars and lateral accretionary wedges on bar margins; (3) trough cross-bedded pebbly sands deposited in channels during low flow stages; and (4) thin ripple-bedded sands and silts, and laminated muds deposited by spillover into abandoned channels and irregularities on bar surfaces.

Short-term flow variations are recorded by thin alternating bar and channel sediments, which were deposited during waning flow, when channels were cut and filled on surfaces of bars formed during flood stage. Longer term variations are recorded by thicker sequences consisting of thin bar and channel deposits formed during high but fluctuating flow, alternating with thick channel deposits that accumulated during prolonged periods of low flow. These braided stream sediments were deposited during ice advance and intitial stages of ice disintegration.

The other type of deposit occurs in the upper part of the terrances and consists of large-scale trough cross-bedded cobble gravels. These sediments accumulated after the drainage network from the disintegrating ice field was fully developed and uniform rapid flow was established.

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