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Principal sediment sources in the northern Gulf of Mexico are the Mississippi and Rio Grande basins, which supply subarkosic sands with highly unstable heavy mineral suites derived from mixed sedimentary, volcanic, plutonic, and metamorphic rocks. Components belonging to the last three groups predominate in the heavy mineral assemblages. Much of the detritus has been transported over very long distances. Technically, the source areas include both cratons and orogens. The distributive provinces are homogeneous, and sands, silts, and clays spread over the entire width of the shelf. The drainage basins of the rivers of western Louisiana, Texas, and the area east of the Mississippi represent less abundant sediment sources. With the exception of the metamorphic and sedimentary suite of the Colorado River, sediments are orthoquartzitic with stable heavy mineral suites, and are derived from the Cretaceous and Tertiary margins of the Gulf Coast basin. Sands from these sources are distributed mainly in the nearshore zone, whereas the clays are carried by Gulf residual currents and deposited on the middle and outer shelf together with finegrained Mississippi and Rio Grande material. The distribution patterns of the two major textural groups, sand and silt-clay, are virtually independent, and in many instances the sand, silt, and clay modes of the same locality have different sources. The sequence of nearshore environments produced by the Holocene transgression has resulted in the deposition of a complex pattern of sediments from a variety of sources.

Modification of the composition of the sand fraction by agents operating in the depositional basin appears to be of little significance except for the removal of pyroxenes by weathering from Mississippi and Rio Grande deposits exposed on the continental shelf during the Pleistocene.

A review of Gulf sediments in the light of theories on tectonic control of sediment properties leads to the conclusion that the tectofacies of the source and depositional areas has little influence on sediment composition in this area. Sediment texture is controlled almost exclusively by depositional environment, which is only to a small extent dependent upon tectonics. Consequently, in the Gulf of Mexico both textural and compositional properties of the sediments are to a large degree independent of tectofacies.

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