Abstract

Recent work along the central Texas coast has suggested that middle Holocene sea level was slightly higher (+ 2 m) than present. This paper discusses some newly-recognized and/or reinterpreted mainland erosion surfaces and beach ridge plains of Holocene age that may represent the geomorphic manifestation of this highstand. Extensive erosion surfaces occur along bay margins, truncate weathered Pleistocene Ingleside sand at elevations of +2 m or more, and are overlain by swash zone and/or other bay margin deposits. Holocene beach ridge plains occur farther seaward from these erosion surfaces, and are underlain by more than 4 m of unweathered, massive to stratified sand. Holocene beach ridge plains are similar in scale to the modern barriers, since they attain elevations of +2.5 m, extend for tens of km along the mainland shore between Matagorda, San Antonio, Copano, and Corpus Christi Bays, and can be 1-3 km in width. Erosion surfaces are interpreted to represent wave ravinement along the shoreline of maximum transgression, whereas beach ridge plains are interpreted to represent progradation after maximum highstand, during sea-level fall to present elevations or lower.