Geologic Framework of Gulf Coastal Plain of Texas

Abstract

The Gulf Coastal Plain of Texas is bounded on the north by the outcrop of the oldest Upper Cretaceous beds, on the south by the outer margin of the present Continental Shelf, on the east by the Louisiana State Line, and on the southwest by the Rio Grande River. The Ouachita folded belt lies under the inner margin of the Coastal Plain and beneath the beds of Jurassic or Cretaceous age. These partly truncated Ouachita folds served, in part, as the foundation on which the Mesozoic and Cenozoic sediments were deposited. Regional tectonics controlled the geological features and their associated sedimentary processes. Partial peneplanation at the close of several periods was followed by rejuvenation of the land areas which resulted in long periods of deltaic deposition. This, together with the downwarping, faulting, and slumping along the successively younger continental shelves formed structural and sedimentary conditions ideal for the trapping of oil and gas. The closed basins and embayments received evaporites and reef development to a minor degree. The migration of the geosyncline southeastward with each period of deposition resulted in the great thickness of sediments underlying the Gulf Coastal Plain. The structural, isopach, and sand percentage maps illustrate: (1) the present structure and position of selected horizons from the Jurassic through the Miocene, (2) the thickness of these sediments, and (3) the ratio of sand to shale and regional facies changes.