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Occurrence of Pseudophragmina sp. as a Possible Indication of Carbonate Bank Deposition in Upper Wilcox (Paleocene-Eocene), Pointe Coupee Parish, Louisiana

Lori L. Nunn, Rowdy C. Lemoine

Paleontologic and sedimentologic analysis of whole-diameter cores from two upper Wilcox sandstones in south-central Louisiana suggests the presence of carbonate bank deposition during the late Wilcox. The larger foraminifera Pseudophragmina sp. occurs in two stratigraphically unrelated sandstones from the upper Wilcox (Paleocene-Eocene) in Pointe Coupee Parish, Louisiana. In Bayou Fordoche field, Pseudophragmina sp. is dispersed throughout an uppermost Wilcox sandstone, which is a 6-m thick unit found 82-m below the top of the Wilcox. In Fordoche field, which is south and downdip of Bayou Fordoche field, numerous individuals of Pseudophragmina sp. are concentrated in two distinct zones within the W-12 sandstone, a relatively thicker (33 m) sandstone that occurs 320 m belo the top of the Wilcox. The downdip W-12 sandstone is stratigraphically unrelated to the updip sandstone; however, the two sandstones are lithologically and faunally similar. The updip sandstone and the Pseudophragmina sp. bearing intervals in the downdip W-12 sandstone are quartzose and glauconitic. In addition to numerous Pseudophragmina sp., they contain globorotalid and globigerinid planktonic foraminifera and smaller benthic foraminifera from such groups as miliolids, lagenids, and nodosarids. Echinoids and mollusks are also present. These fossils are dispersed throughout the updip sandstone and are concentrated in two separate zones within the downdip W-12 sandstone.

This "Pseudophragmina" facies in the upper Wilcox is faunally and lithologically similar to facies that are related to modern submarine carbonate banks in the Gulf of Mexico and to reef facies reported for subsurface Tertiary units in the Gulf Coast. The substantial accumulations of Pseudophragmina sp. in these two sandstones in the upper Wilcox may have been derived from a nearby carbonate bank and, if so, indicate that during the late Wilcox warm, shallow shelf conditions prevailed. The possible presence of a carbonate bank is also notable because of its potential as a petroleum reservoir.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.