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Examination of cores from the upper Smackover Formation from 30 wells in east Texas confirms the presence of a belt of blanket high-energy ooid sandstone throughout much of the area. Pockets of lower energy deposits within this ooid grainstone belt are characterized by pellet-Favreina packstones and
grainstones and ooid-rhodolite packstones and grainstones. In the easternmost part of the study area, ooid grainstones grade updip into lower energy lagoonal facies including pellet and Favreina wackestones and packstones. These lagoonal deposits are not as widespread to the west. Lower in the Smackover, low-energy skeletal, pellet and oncolite wackestones and packstones dominate. Two cores contain coralgal fragments suggesting nearby reef development.
The overlying lower Buckner Formation is composed dominantly of red beds and evaporites deposited in a sabkha setting. The presence of thick red beds in cores from the western part of the study area suggests a strong continental influence. Anhydrite is the major evaporite mineral in the lower Buckner. It is present as displacive mosaic and nodular mosaic masses in red beds and dolomitic mudstones. Partial preservation of some original gypsum crystal outlines provides evidence for lesser amounts of primary evaporite precipitation. Small amounts of halite are present in some lower Buckner red beds and associated with anhydrite to the west. Environments and depocenters within the Buckner are thought to have ben partly controlled by movement of the underlying Louann Salt and by rejuvenati n of basement structures.
Major structural influences on Smackover and Buckner deposition or present distribution include the Mexia-Talco fault system, the Sabine uplift, and Louann salt structures. Movement along the Mexia-Talco fault system began in Late Jurassic time and may have affected Smackover and Buckner deposition to an as yet undetermined extent. The extent of the influence of the incipient Sabine uplift on deposition in east Texas has not been determined, although studies to date suggest that it had a significant effect on facies development and on the configuration of the Smackover-Buckner carbonate shelf and associated basin.
The major influence of Louann Salt movement on Smackover and Buckner deposition is confined to the western half of the study area. Salt movement began after the close of Smackover time. Withdrawal of Louann Salt into ridges formed a series of strike-trending linear troughs in the western part of the study area. The Buckner Formation thickens dramatically within the linear troughs, suggesting possible salt movement during Buckner time.
A second linear zone of thickened Buckner section, apparently unrelated to Louann Salt movement, lies to the northeast of the area of salt structures. This strike-oriented Buckner depocenter is well developed in the east and pinches out to the west. Salt is present within the Buckner in the western part of the depocenter.
Cross sections constructed from electric logs and data from core analysis demonstrate these relationships and may help delineate potential areas for hydrocarbon exploration.
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