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The Petrology and Origin of the Lafayette Gravel: Part 1. Mineralogy and Petrology

Paul Edwin Potter
The Journal of Geology
Vol. 63, No. 1 (Jan., 1955), pp. 1-38
Stable URL: http://www.jstor.org/stable/30066134
Page Count: 38
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The Petrology and Origin of the Lafayette Gravel: Part 1. Mineralogy and Petrology
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Abstract

Extensive chert gravels underlying the Smithland and higher erosion surfaces of the uppermost portion of the Mississippi embayment are considered remnants of three coalescing alluvial fans related to the ancestral Mississippi, Cumberland-Ohio, and Tennessee rivers. The shape and topographic form of the largest of these remnants, the Smithland surface of western Kentucky, best illustrates an alluvial-fan origin. The ancestral Tennessee and Mississippi alluvial fans have contrasts in direction of sediment transport, heavy-mineral suites, metamorphic quartz, and sand roundness. Chert pebble roundness is similar, however, and experimental abrasion data indicate that the maximum roundness of 19-23-mm. chert pebbles can be obtained in approximately 70 miles. Available evidence suggests that a large but indeterminate portion of the primary and secondary modes was derived less than 100 miles from the Mississippi embayment's periphery.

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