The late Pleistocene and Recent sediments, faunas, and geomorphology were mapped in the vicinity of Sabine Lake, in an area that straddles the Texas-Louisiana state line and extends into the Gulf of Mexico. The former valley of the Neches and Sabine rivers is entrenched into oxidized Pleistocene deposits to a minimum depth of 120 feet at the Gulf of Mexico shoreline. This valley has been filled in by the streams and closed off at its southern end, except for Sabine Pass, by prograding of the Gulf shoreline to form the present lake estuary, Sabine Lake. The erosion and subsequent alluviation were caused by a fall and rise in sea-level due to waxing and waning of continental glaciers late in Quaternary time.

Lithology and fauna, especially the Foraminifera, were determined from cores and clam-shell samples taken in the Sabine Lake estuary and Gulf of Mexico nearshore neritic environments. No

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lithologic criteria for distinguishing these two environments were evident in the surface sediments or in core samples taken 3 feet and 6 feet below the surface.

Foraminiferal biofacies, however, do differentiate clearly the estuarine and the nearshore neritic environments. The species and their percentages in the bottom sediments of Sabine Lake differ from those of the Gulf of Mexico, and from those in the core samples from 3 and 6 feet. The biofacies of the core samples from under the lake are similar to those of the present Gulf, indicating greater circulation of saline waters from the Gulf of Mexico before the south end of Sabine Lake was restricted.

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