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A gravity study of about 306 mi2 (793 km2) of west-central Calcasieu Parish, Louisiana, was completed. The data used were from a very old Bouguer map of unknown origin. The data on the map were obscure, so a grid was drawn over the map and the points of intersection and the gravity contour lines were digitized. With the Bouguer values, these points served as input to least squares and model analysis systems.
The least squares trend surfaces were calculated and mapped using STAMPEDE, an IMB system modified by Wright State University. The data were processed by an IBM 370 computer and mapped with a Calcomp plotter.
The residual map was generated by calculating a first-order surface and subtracting it from the Bouguer map. The similarity between the residual gravity map and the structure contour maps on the Vinton and Edgerly salt domes is striking.
Models using densities from five deep wells and an array of vertical prisms with square cross sections were calculated. A theoretical gravity map drawn from the models is almost identical to the residual gravity map. Profiles of the theoretical gravity and the residual gravity are compared. These profiles match exactly over the salt dome areas and show little divergence elsewhere.
Gravity studies, no matter the age of the survey, are still a definitive exploration technique, especially in areas of marked density contrasts.
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