When The Mississippi Met the Atlantic

July 29, 2016

Eric Carson is a geomorphologist — which, as he describes it, is basically a "double major" in geology and geography. Some time ago he and a few colleagues started asking a question about a geologic shelf where the Mississippi meets the Wisconsin River. The results could have meant nothing, or they could have meant a major new revelation about the Mississippi's historical path to the ocean.

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To reconstruct the history of Mammoth Cave, Kentucky, it's necessary to invoke several changes in river patterns, mainly ancestral versions of the Ohio. There was a sharp drop in fluvial base level around 2.5 Ma (as dated with Al/Be isotopes) that had a remarkable effect on the cave pattern -- accelerated development of lower levels, accompanied by dissection of gently graded surfaces (Pennyroyal Plateau, Mitchell Plain), and apparently caused by diversion of the northward flow of water westward as the Teays River. We've been wondering whether that diversion alone was sufficient to account for all the downcutting. If the Mississippi was only a rudimentary precursor of its present self, that would answer a lot of our questions! Would like to hear more about your research (and perhaps vice versa). I'm a hydrologist, rather than geomorphologist, but the two fields complement each other. ---- Best regards, Art Palmer
(See 2001 GSA Bulletin 113:7, p. 825-836 and 1991 Bulletin 103:1, p. 1-21.

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