A view of late glacial runoff from the lower Mississippi River valley
- Army Engineer Waterways Experiment, Vicksburg, MS (United States)
Thousands of cubic kilometers of massive coarse-grained Late Wisconsin glacial outwash underline the Mississippi alluvial plain, however, the deposits are exposed at the surface primarily only in the Eastern Lowlands. There the valley train deposits form a series of low, flat terraces characterized by a distinctive pattern of relict braided channels. The terrace levels reflect episodes of meltwater release and possibly catastrophic flood events, but precise correlations to Midwest events have not been possible. The detailed chronology of late glacial runoff in the valley is not resolved, but certain key events have been temporally defined. Diversion of the Mississippi River from the Western to the eastern Lowlands began about 16,000 B.P. The high and intermediate terrace levels formed between 14,500 and 11,000 B.P. during the peak of late glacial runoff: the intermediate level was abandoned and had wide-spread human habitation by 10,000 B.P. Following a lull in runoff after 11,000 B.P., a diversion of the river through Thebes Gap and the formation of the well-defined Charleston Fan in southeast Missouri was possibly triggered by a sudden and brief meltwater release event. Sedimentological and archeological evidence suggest this occurred between 10,500 and 10,000 B.P. By about 9,800 B.P., the river had ceased carrying meltwater and was flowing in a meandering regime. Because most outwash in the valley is buried, opportunities for direct investigation will always be limited. However, indirect study of outwash via impacts on sedimentation in tributary valleys, banding in loess deposits, and distribution of ice-rafted erratics should yield new chronostratigraphic evidence.
- OSTI ID:
- 5589591
- Report Number(s):
- CONF-921058--
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Journal Name: Geological Society of America, Abstracts with Programs; (United States) Vol. 24:7; ISSN GAAPBC; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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