Identification of a −15 m Wisconsin shoreline on the Texas inner continental shelf

The maximum sea level position during the middle Wisconsin (oxygen isotope stage 3) is controversial, it being interpreted as anywhere from at or above present-day levels to −85 m. High-resolution seismic, lithologic, paleontologic, and radiocarbon data from the east Texas continental shelf were used to map a stage 3 shoreline. The shoreline was placed in a regional context with a study of the Texas shelf, based on seismic profiles, core, and platform boring descriptions, that identifies the stage 3 maximum flooding surface and the stage 2 sequence boundary. These surfaces were then traced up-dip on the east Texas shelf where a shore parallel escarpment was recognized. Landward of the escarpment the stage 3 maximum flooding surface is amalgamated with the stage 2 sequence boundary. Therefore, the location of the escarpment marks the up-dip limit of stage 3 deposits and a stage 3 shoreline. Lagoonal sediments with in situ brackish water fossils on-lap the escarpment. Seaward of the escarpment, remnants of barrier island facies have been preserved as a bank, Freeport Rocks Bathymetric High, located in −18 m of water. The shoreline (adjusted for subsidence) is located at −15±2 m, which is shallower than what oxygen isotope and coral records indicate.