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A clean, generally well-sorted, commonly porous, Jurassic sandstone separates marine lower Smackover carbonate mudstone from nonmarine redbeds of the Norphlet Formation in parts of southern Mississippi, southwestern Alabama, and northwestern Florida. Various workers have considered this sandstone unit to be marine, nonmarine, or a combination, and have called it basal Smackover, Norphlet, or Denkman. "Denkman sandstone" was proposed for this unit by Murray, who designated the Lion No. 2 Denkman, Sec. 22, T17N, R4E, Rankin County, Mississippi, as the type section. The Denkman locally exceeds 1,000 ft in thickness and is a lithologically distinct, mappable unit. Nevertheless, it is included in the Norphlet Formation by the industry and in this paper it is called the Denkman Sandstone Member of the Norphlet Formation.
The Denkman is overlain generally without gradation by nonsandy basal Smackover carbonates, but is gradational downward into redbeds, the more characteristic lithology of the Norphlet. Regionally, the Denkman grades updip into conglomeratic redbeds interpreted to be alluvial fan and fluvial deposits. The Denkman sand typically consists of well-sorted, fine- to medium-grained, rounded and commonly frosted, quartz grains with some feldspar, chert, and rock fragments. The section is commonly crossbedded and does not contain fossils or carbonate beds. The Denkman usually has good permeability and intergranular porosity ranges up to 25%. Unlike sandstone beds in the Smackover, the Denkman rarely contains carbonate cement. The Denkman sandstone is reddish in its lower part and may contain s me thin shaly beds. Regional distribution of the Denkman suggests a sand source on the north and east. Stratigraphic relations, lithology, and sedimentary structures suggest a nonmarine fluvial to eolian origin for most of the Denkman sandstone. Locally the uppermost part has been reworked during Smackover transgression. The Denkman Sandstone Member marks the top of the Werner Anhydrite-Louann Salt-Norphlet Formation deposition cycle.
The Denkman sandstone commonly has excellent reservoir properties and has been found productive at the Pelahatchee, Prairie Branch, Archusa Springs, East Nancy, South State Line, Big Escambia Creek, Flomaton, Little Escambia Creek, Jay, and Blackjack Creek fields. It is and will continue to be an important exploration objective along the southeast part of the Jurassic trend.
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