ABSTRACT

The northeasternmost part of the East Texas Basin is a simple area in which to observe the lithologic patterns of the sedimentary wedge consisting of the Late Jurassic Smackover Fm., Buckner Fm. and Gilmer Fm. The area has not been complicated by much salt movement or "basement" faulting and extrabasinal influences during deposition were minimal. Additionally, 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 is largely anhydrite and red beds. The Buckner grades into the Smackover to the south and thus pinches out downdip. The Gilmer (also referred to as the Haynesville or Cotton Valley Massive Lime by industry workers) consists largely of "clean" limestone that grades updip into sandstone and downdip into shale or muddy limestone.

These gross patterns coupled with critical interpretations of paleoenvironment based on more detailed lithologic observatons lead to a synthesis of the area's 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. North of the shoreline complex a starved area filled with coastal plain red beds and hypersaline lagoon gypsum. Halite precipitated in the most restricted areas of the lagoon. The Buckner complex prograded basinward concurrently with the Smackover paralic facies creating a sedimentary platform that projected forty-five miles into the basin.

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

A number of workers have considered the Buckner along the Gulf Coast to be a member of the Haynesville Formation but the nature of the Buckner as described in this report indicates the Buckner is more appropriately considered to be of formation rank in northeast Texas.