ABSTRACT

In marked contrast with the Ingleside barrier chain of southwest Texas that delineates the late Pleistocene Sangamonian Interglacial mainland shoreline, new data from numerous drillcores and study of landforms in the southeast Texas-southwest Louisiana coastal plain provide different results. They reveal that, contrary to earlier claims, numerous topographic ridges and other features, composed of late Pleistocene deposits are not of coastal barrier or beach ridge origin. Fannett Barrier, covered by a strandplain of recurved beach ridges that evolved along the prograding shore of a Gulf embayment, is the sole exception. Silty sandy nearshore and sandy estuarine, respectively shoreface sediments, underlie the Orange and Smith Point-Pine Island localities at shallow depths. Sets of closely-spaced, arrow-straight, narrow lineaments imprinted by tectonic processes, previously have been taken for beach ridge plains that cover barrier surfaces.

The "East Ingleside Trend" turned out to be a misnomer. Although nearshore Sangamonian deposits abound in the shallow subsurface, with the exception of Fannett Barrer strandline, indicator landforms are absent from the subsurface. The paleosalinities of the sedimentary units in our cross sections, suggest that, at the peak of the Sangamonian transgression, the mainland shoreline was located significantly Gulfward of Houston Ridge and Orange County locations but landward of Smith Point-Pine Island. Estuarine water bodies probably extended well inland of the Smith Point-Fannett line.