ABSTRACT

This research was designed to investigate the origin and chemical evolution of subsurface brines in a modern coastal marine sabkha by assessing the major-element geochemistry of the brines. The study area is in the Wind Tidal Flat area of Laguna Madre, Texas, which is approximately 80 km south of Corpus Christi. This area is an active sabkha composed essentially of quartz sand. Its surface is covered extensively by blue-green algal mats.

A system of 20 well sites has been established across the 22-km width of the sabkha. The geochemistry of the subsurface waters was determined at each site from two wells (1.8 m and 3.8 m deep) and from a shallow trench dug to intersect the water table. The chemical data were collected during two sampling periods (August 1979 and March 1980).

The essential conclusions of this study are 1) the subsurface brine is a sodium chloride solution of continental and marine origin; 2) recharge of the marine water is through the process of flood recharge during which Laguna Madre waters are driven across the surface of the sabkha by high winds; 3) recharge of the continental waters is apparently by ground-water movement to the coast; and 4) the brine evolves chemically during evaporitic concentration by the precipitation of calcium carbonate and calcium sulfate minerals.