ABSTRACT

A coquina, which probably correlates with the Ingleside complex of the Pleistocene Beaumont Formation, crops out discontinuously along the mainland shore of Laguna Madre and extends approximately 10 km southward from Baffin Bay, Texas. These outcrops are among the only lithified bedrock exposures along the South Texas coast. The coquina occurs as a low bluff <1 m high in the surf zone and has paleoenvironmental significance and well-displayed erosional features.

Its fossil shells are nearly identical with those found in localized shell beaches immediately seaward on central Padre Island, suggesting that the coquina represents a lithified Gulf-beach shell deposit that predates the barrier island. The coquina shows intense karstification, which presumably occurred when sea level stood much lower than it now does. Steep-walled, cylindrical solution pipes 60 cm or more in diameter and 1 m or more deep extend vertically downward into cavernous openings beneath the outcrops. Reddish-brown laminated caliche crusts coat the coquina in many places, often extending downward into the solution pipes. The crusts probably formed beneath a humic soil layer during a previous low stand of the sea and may evidence a wetter and warmer climate than the present one in South Texas.