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The AAPG/Datapages Combined Publications Database

GCAGS Transactions


Gulf Coast Association of Geological Societies Transactions
Vol. 31 (1981), Pages 7-17

Depositional and Diagenetic Cycles in Smackover Limestone-Sandstone Sequences, Lincoln Parish, Louisiana

Wayne M. Ahr (1), Gregory J. Palko (2)


The Jurassic upper Smackover Formation in Lincoln Parish, Louisiana, consists mainly of nonskeletal grainstones, argillaceous, anhydritic dolomitic mudstones to wackestones, and bioturbated to graded siliciclastics. Two shoaling-upward cycles, the "A and B limes" of local stratigraphers, were identified. These grainstone deposits accumulated as tidal bars on east-west trending paleo highs ("salt structures") which parallel regional depositional strike. The salt ridges originated during middle Smackover deposition along the northern rim of the north Louisiana salt basin and produced a "slope-break" on the regional Smackover ramp.

Between the salt ridges in the study area is an interridge trough or withdrawal basin. The strike-trending trough was filled episodically with mixtures of grain carbonates, sandstones, siltstones, and shales. The siliciclastics include fining-upward litharenites and graded, alternating grainstone-sandstone bedsets. The textural grading probably reflects strong but intermittent wave drift or storm surge currents that moved from east to west along the flanks of the salt highs. The finer grained rocks occur in the withdrawal basin center.

Diagenetic products observed in thin sections indicate that the Smackover carbonates were exposed to early marine, meteoric phreatic, and subsurface diagenesis. Marine diagenesis included micritization and isopachous aragonite rim cementation. Fresh-water diagenesis included leaching of allochems and cements and precipitation of blocky calcite rim and mosaic cements. Subsurface diagenesis included precipitation of pore-filling and replacement anhydrite, silicification, and stylolitization. The distribution of early diagenetic effects basically follows the trend of the salt ridges.

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