The Stratigraphy of the Trinity Group, East Texas Basin

FRENCH, VICTORIA L., Baylor University, Waco, TX

The Lower Cretaceous Trinity Group of the East Texas basin contains formations that have produced oil for a number of years, and while they have been the subject of considerable discussion, little has been said about their character and regional distribution over the entire basin. This regional treatment is critical to an understanding of the tectonic history of the East Texas basin.

The Trinity Group consists of facies varying from fluvial sands to marginal marine limestones and shales. In the East Texas basin, Trinity rocks were initially deposited during basinal subsidence and form a wedge of sediments that thicken rapidly eastward. Early Trinity deposition began as clastics were shed from highlands to the north and west and then were deposited within the basin by prograding deltaic systems. Sediment was first deposited as channel-fill and point-bar deposits. Toward the basin, fluvial sands were deposited as destructive deltaic facies. True marine sedimentation was confined to the extreme southeastern part of the basin.

Trinity deposition reflects a series of minor transgressive and regressive pulses, with environments ranging from deltaic and shallow

open shelf to restricted lagoon. With the buildup of the Stuart City reef system along the southern margin of the basin isolation occurred. During late Trinity, seas covered the entire basin and a large area of the stable Texas platform resulting in deposition of a thick, shallow, open-marine limestone and shale sequence, which marks the end of Trinity deposition.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)