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The AAPG/Datapages Combined Publications Database
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Jurassic sedimentation in the area reflects the influence of numerous Appalachian structural salients. These features include the Pensacola arch, Chattahoochee arch, Brevard anticline, and the southwest extension of the Appalachian structural front, as well as several pre-Jurassic igneous plugs. A great influx of clastic material invaded the seaward margins of these structures, obliterating recognized formation boundaries in the Late Jurassic Norphlet, Smackover, and Haynesville Formations.
An anhydrite member of the Louann Salt, previously unnamed, was found in wells from Clarke, Monroe, and Wilcox Counties. This anhydrite, the Pine Hill Member, is at the top of the Louann Salt where salt is present and reaches a maximum recognized thickness of 210 ft.
The Norphlet of Alabama is typically a red sandstone or conglomerate containing igneous pebbles, anhydrite, and minor amounts of shale. In much of the area it grades upward into a gray neritic sandstone which is believed to be equivalent to the Smackover. The Norphlet-Smackover contact in this facies cannot be distinguished but the upper gray sandstone is considered to be a good exploration target. In Choctaw and northern Washington Counties, typical Smackover and Norphlet sedimentary rocks can be recognized. In this area the oolitic facies of the upper Smackover is a major objective, with production established at Toxey and Choctaw Ridge fields.
The Tombigbee depression, a depocenter for Jurassic sediments, was so named because the axis of this low follows the Tombigbee River along the east side of Washington County. During the time of Haynesville deposition this depression received large quantities of anhydrite and salt. On the northeast along the shoreward margin of the evaporites, a shoal facies developed in a relatively narrow NW-SE trend. This facies has a major exploration potential.
Cotton Valley clastic rocks include sandstone and conglomerate typical of the Schuler facies of Mississippi. Igneous pebbles also are common. Seaward, the Dorcheat facies is present, and with it a more favorable environment for oil accumulation.
This paper is not so much a documentation of the presently recognized Jurassic sediments as it is an interpretation of the projected facies and environments based on geologic concepts. Alabama and panhandle Florida will become important areas of Jurassic production in the near future.
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