GRAVITATIONAL STUDY OF THE HASTINGS SALT DOME AND ASSOCIATED FAULTS IN BRAZORIA AND GALVESTON COUNTIES, TEXAS

Salt domes are important geological structures, because they often form structural traps for oil and gas accumulation. Over five hundred salt domes exist in the United States Gulf Coast region and the Hastings Salt Dome is one of the many identified and it is an economically important salt domes in the region. The study area extends from south Harris county to north-east of Brazoria and north-west of Galveston counties.

Gravity surveying is a passive, geophysical method for investigating structural features based on differences in rock densities within the subsurface. Gravitational force, which is density dependent, is measured by using a gravity-meter. The CG-5 Scintrex Autograv gravity-meter is used in this study to measure the variations in gravitational fields within the study area.

Five hundred and thirty-seven gravity readings were collected with a data spacing of one-third to one-quarter of a mile over the study area. The geographical coordinate for each gravity reading was obtained with the aid of Trimble NOMAD gps unit. This relatively close station spacing approach is expected to produce a highly resolved gravity anomaly map. Magnetic dataset over the study area was downloaded from PACES (Pan American Center for Earth and Environmental and Studies) database. This magnetic dataset shows the distribution of total magnetic intensity. LiDAR data over the study area was used to create a DEM (Digital Elevation Model), in which elevation values were extracted from. Eleven well logs were used to inspect for effects of salt diapirism in the subsurface. Remote sensing techniques and creekology concepts were adopted to examine for surface imprint resulting from the diapiric effect of Hastings Salt Dome.

One objective of this this study is to produce a Bouguer Anomaly map of the study area. Bouguer Anomaly reveals lateral variations in rock density in the subsurface. Salt domes show low or negative anomaly signatures in a Bouguer Anomaly map, because they are low density rocks relative to their surroundings. The outcome of this study will improve on understanding the location and extent and the estimated depth of the Hastings Salt Dome.