SWENSON, DAVID R., Energy Development, Bellaire, TX

ABSTRACT: Regional Lithofacies Patterns of the Louark Group in Northeast Texas

The northeasternmost part of the East Texas basin is a relatively simple area in which to observe the lithologic patterns of the Late Jurassic Smackover, Buckner and Gilmer sedimentary wedge. The area is not complicated by much salt movement or basement faulting, extrabasinal influences were at a minimum, and seismic and subsurface control is moderately dense. Throughout most of the area the Smackover is a shallowing-upward carbonate capped by a variably dolomitized grainstone. The overlying Buckner grades from updip red beds to downdip anhydrite with red beds overlying anhydrite in most of the area. The Buckner grades into the Smackover and thus pinches out downdip. The Gilmer consists largely of limestone that grades updip into sandstone and downdip into shale or muddy limestones.

Those gross patterns, coupled with critical interpretations of paleoenvironment based on more detailed lithologic observations, lead to a simple synthesis of geologic history. With marine inundation of the east Texas area and a lack of terrigenous influx, carbonate began to accumulate and a Smackover shallow marine/shoreline complex prograded basinward. Behind the shoreline complex, a starved area developed whose landward side filled with a red bed wadi plain and marine side with gypsum precipitated in a hypersaline lagoon. The most restricted areas of the lagoon saw halite precipitation. The Buckner complex prograded basinward behind the Smackover paralic facies creating a sedimentary platform that projected 70 km into the basin.

A marine transgression reestablished limestone deposition of the Gilmer on the Buckner platform. The shallow-marine Gilmer prograded across the shallow platform back to the location of the youngest Smackover shoreline. The shoreline facies aggraded at the platform edge until Terrigenous clastics in the western part of the area near the top of the Gilmer evidently record a short-lived regression.

Since the Buckner/Gilmer boundary represents a more profound depositional change than the gradational Buckner/Smackover contact, it seems appropriate to consider the Buckner a formation rather than a member of the Gilmer.

AAPG Search and Discovery Article #90989©1993 GCAGS and Gulf Coast SEPM 43rd Annual Meeting, Shreveport, Louisiana, October 20-22, 1993.