Depositional History of Gulfian Cretaceous of East Texas Embayment

Abstract

Regional aspects of the depositional environment of Gulfian Cretaceous rocks in the East Texas embayment have been investigated by a combined stratigraphic and paleontologic approach. Only readily available information from electrical and sample logs and simply made paleontologic determinations have been employed. Almost 3,000 wells were used for control. The program provided structure, isopach, three-end-member lithofacies, sandstone-shale-ratio, number-of-discrete-sandstone bodies, shale-color, and biofacies maps. This approach revealed essential continuity of structural behavior throughout the Gulfian, but showed a major change in the direction of the source of terrigenous clastics from northeasterly in early Gulfian time to westerly during the remaining Gulfian. Biofa ies and lithofacies data indicate that the seaward edge of the Gulfian Cretaceous continental slope lay in the position of the Angelina-Caldwell flexure, and that on the south, deep open ocean existed. North of this flexure lay an epicontinental sea crossed by various current systems. Evidence suggests that marine deposition occurred westward for a considerable distance beyond areas in which Gulfian Cretaceous rocks are preserved. It is proposed that the black shales characterizing parts of the Gulfian Cretaceous within the area owe their color to postdepositional reducing conditions caused by low permeability related to fine grain size. The Sabine uplift episodically changed its position with respect to sea level, resulting in varying effectiveness as a barrier to sediment and water tra sport. During part of early Late Cretaceous time the uplift apparently was slightly emergent and served as a minor source of sediment. The simple parameters studied delineated the areas now known from drilling to produce hydrocarbons as prospective for production of hydrocarbons.