ABSTRACT

This paper presents a regional isopachous, lithofacies and stratigraphic study of the Jurassic sediments in the anticipated producing trend of Mississippi and Alabama. Jurassic deposition in the study area was affected by three major tectonic factors; a southwestward subsurface extension of the folded Appalachians, regional ancestral faulting, and salt uplift. These factors are manifested in the distribution of the sediments and in facies variations.

The Middle and Lower Smackover is characterized by dense argillaceous carbonate deposits. Locally, it develops a littoral facies with good sandstone porosity. Upper Smackover carbonate sediments are zoned into a porous sandy facies, a dense dolomitic facies, and a porous oolitic facies. Tectonic influences are first noticed in Upper Smackover sediments and appear to culminate during Cotton Valley deposition.

Haynesville deposits include a basal Buckner anhydrite member and an overlying anhydritic carbonate section which grades shoreward into a porous sandy facies. Excellent reservoir rocks have been found in the transitional zone between the restricted shelf and littoral environments.

The Cotton Valley has been subdivided into the Schuler and Dorcheat facies. The Schuler facies is predominantly a red beds section representing a paralic environment. It is a coarse grained clastic. The Dorcheat facies, a fine grained clastic is an open neritic shelf deposit with grain size increasing towards the shoreline. Excellent reservoir properties are present in all Cotton Valley sands.