ABSTRACT

The large volume of literature available on Gulf Coast sedimentology, along with recent advances in computerized analytical methods, now enables more detailed work to be accomplished. Numerous grain-size (automated settling tube) and heavy mineralogical analyses have been conducted on sand samples from the northeastern Texas Gulf Coast. Analyses of local point-bar samples result in the delineation of major river sand sources in the region. Kyanite/garnet/hornblende+pyroxene ratios seem to be the most useful criteria for distinguishing these sources. Grain-size data show combinations of discrete modes characteristic of each river system, whereas the subaerial delta lobes of these rivers consist of finer, better sorted sands, which are believed to represent the coarsest particles transported in suspension. Beach sands are slightly finer and much better sorted than wave-dominated delta sands.

The oldest sands of Galveston Island were derived from the Trinity River, implying a possible deltaic origin for the island. However, most of the island is comprised of Mississippi River, Brazos River, and Trinity-Sabine River sands, mixed in approximately equal proportions, suggesting an offshore Pleistocene source for these features. These sands were deposited on an irregular Pleistocene erosional surface, resulting in dramatic thickness variations. Modern offshore sands and those currently being accreted to barriers, contain a high proportion of Mississippi River sand. This change results from the depletion of offshore mixed sands and marks the onset of barrier retreat.

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