Abstract

Multiple, discontinuous sandstones of the Wilcox Group in central Louisiana were deposited in fluvial, deltaic, and marine sedimentary environments in the Tertiary Gulf of Mexico basin. Prolific hydrocarbon reservoirs developed in association with positive structural features or where sedimentary characteristics were favorable. Regional stratigraphic correlations are difficult because the Wilcox Group contains numerous complex depocenters. To delineate the occurrence of hydrocarbon-bearing sediments and to promote further exploration, a five-fold lithostratigraphic framework (units I-V, in descending order) is proposed for the Wilcox Group on the basis of its sedimentary character as interpreted from well logs. Lithostratigraphic unit thickness and sandstone content were mapped within 22 parishes. All units produce hydrocarbons, although production is geographically variable. Production in the updip Wilcox is the greatest in unit III, whereas units I and 11 are most productive in the downdip Deep Wilcox shelf-margin trend. Units V and IV represent the initial deposition of sand-rich sediment into the Gulf of Mexico following the Midway transgression. Transgression marked by unconformities and the Cane River MArl above unit I terminated Wilcox deposition. Wilcox sediment sources were located to the northeast and northwest. ALl units display a strong north-south isopach grain in the northern two-thirds of the study area; however, east-west-oriented sandstone packages are present along the paleoshelf margin. ALluvial valley (progradational and aggradational) and valley interfluve (retrogradational-coastal onlap) deposition can be discerned from well logs.

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