Depositional systems in the Jackson Group of Texas: their relationship to oil, gas, and uranium
Five main depositional systems of the Jackson Group in Texas are delineated through regional outcrop and subsurface investigation. Dominant element in the central and eastern Texas Gulf Basin is the Fayette fluvial-delta system (bounded by Guadalupe River on the south and Neches River on the east) consisting of dip-oriented, lobate wedges of sands, muds, and lignites. Vertical sequence in updip subsurface and outcrop grades upward from marine muds through delta facies into fluvial sands and muds, reflecting net regression and progradation of the system. Longshore drift of sediments from the delta system contributed to the South Texas strandplain-barrier bar system, consisting of strike-trending sand bodies interbedded with marine and lagoonal muds. Landward of the strandplain-barrier bar system and extending into outcrop is a lagoonal-coastal plain system consisting of muds, local lignites, and minor, dip-oriented channel sand units. Gulfward of the strike-trending strandplain system is the South Texas shelf system, formed of marine muds derived largely from the delta system to the northeast. Beneath the South Texas strandplain-barrier bar and Fayette delta systems and extending eastward into Louisiana and Mississippi is the Yazoo-Moodys Branch shelf system consisting of marine, fossiliferous muds and minor glauconitic marls. Texas Jackson delta and associated systems are comparable to depositional systems of other Eocene units (Lower Wilcox and Yegua) of the Gulf Basin as well as the Holocene Mississippi delta and related systems of the northwestern Gulf of Mexico. Delineation of depositional systems and component facies facilitates definition of significant mineral trends (oil, gas, lignite, and uranium) that show the relationship between existing and potential areas of production.