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A completed 3-yr study of the sources and consequent distribution of late Pleistocene sand on the northern Gulf shelf clarifies paleogeography and alluvial identification. Techniques used to determine the sources of sand are: the Fourier technique (which differentiated sands from different source terranes on the basis of the shapes of quartz sand grains), mineralogic analysis (which identified the composition of the source terranes that contributed each quartz-shape type), and an evaluation of the source terranes drained by each of the southern United States rivers (thereby linking each shape type to a particular river). These data and the mapped distribution of sand deposited on the shelf by each of these rivers during the late Pleistocene lowstand indicate distribution atterns have not been modified by modern shelf currents to any great extent, and thus record the late Pleistocene paleogeography of the shelf. These distributions show, among other things, the locations of the late Pleistocene alluvial valleys of each of the southern United States rivers, and identify the sources of shelf-edge deltas off the coasts of Texas and Louisiana that were detected by shallow seismic analysis.
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