ABSTRACT

Lithologic and thickness data on Upper Jurassic rocks of the Cotton Valley group, Upper Gulf Coastal Plain, were interpreted from electric and sample logs, and correlations were established from Arkansas and Louisiana into Texas, Mississippi, and Alabama.

Units mapped include the total Cotton Valley, the Schuler formation, and the Bossier formation. Maps included are based on isopachs, lithofacies, shale ratios, and vertical variability. Sand distribution in the Schuler is represented by a "number of sands" map, a "slice" map of the top thousand feet, and a "tripartite sand distribution" map.

The Bossier formation is a regional wedge of thick black shale merging updip into a fringe of non-marine shale and sand. The Schuler formation overlaps the Bossier. Its downdip aspect is predominantly marine. It thins updip through a transition zone of maximum shale percentage and maximum number of sands into a non-marine section of coarse clastics.

It is believed that the Schuler formation was deposited on an unstable shelf flanking the Gulf Coast basin and receiving a supply of clastics from the north and northeast. The North Louisiana Interior Salt Dome basin was separated from the East Texas basin by a shelf of less subsidence in the region of the Sabine uplift.

The marine sands of the Schuler formation were presumably deposited by longshore currents carrying clastics westward from a major delta in northeastern Louisiana and western Mississippi. Facies patterns developed on all of the maps bear a definite relationship to the Cotton Valley producing trends in northern Louisiana.

FOOTNOTE 1. Based on a dissertation for the degree Master of Science, submitted to the Graduate School Northwestern University, 1954. Presented by title before the association at the St. Louis meeting, April, 1954.

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