Corpus Christi Structural Basin Postulated from Salinity Data

Abstract

Water wells completed in the Lissie and Beaumont show that artesian conditions exist in spite of supposed lenticularity. Analyses of 1,400 water samples yield a salinity map based on regional, smoothed-out lines of equal chlorine concentration (isosalinity lines) ranging from 500 to 4,000 parts per million. Inability to correlate individual sands requires that the Lissie-Beaumont be treated as a single water sand. Sands, the water of which was sampled, lie beneath a shallow zone of highly saline ground water which is replaced under sandy soil by fresh water of surface origin. The strongest Lissie-Beaumont water analyzed had 9,578 parts, and immediately beneath the Lissie is water with more than 22,000 parts of chlorine. After analogy with the Woodbine artesian sand of the East Texas basin, where isosalinity lines and structural contours are parallel, a wide swing of the lines around the head of Nueces-Corpus Christi Bay is considered to establish a Corpus Christi structural basin, provided the hypothesis of the down-dip flow of surface waters mixing with the original brines may be accepted as the explanation of the observed distribution of salinity in both regions. This hypothesis is favored. Adjustment of the ancient, high-level delta of Nueces River of the Pleistocene to the postulated structural basin, and entrenchment in it of the present Nueces River with its drowned-valley bays, support the structural interpretation of the salinity map. Outside the basin the lines are parallel with the gulf shore line. The Beaumont outcrop in Nueces and San Patricio counties is the area covered by the survey. Barton's top-of-salt contours for salt domes suggest that the other bays of Texas may lie in structural basins. Theoretical stages in the evolution of mixed waters of coastal-plain aquifers (reservoir beds) are developed, several being found which could produce the observed salinity gradients of Corpus Christi and East Texas. Opposing interpretations are briefly discussed. The probably varied nature of the connate waters of the Pleistocene may require a combination of methods to explain the observed salinity gradients with the numerous local chlorine highs. One of the highs covers a producing gas field. Other highs are believed to be associated with diastrophic structure. Some are probably due to lenses of impervious sediments obstructing down-dip flow in the water sands. Their pattern does not seem to be that of End_Page 317------------------------------ shore-line features, such as lagoon and bay basins. The structural interpretation of the local chlorine highs is not studied in detail.