TEDESCO, WILLIAM A.
University of Mississippi, Oxford, MS

Abstract: An Eolian Facies Within the Upper Jurassic Smackover Formation, Tchula Lake Field, Mississippi

The Upper Jurassic Smackover Formation in Mississippi is primarily composed of a regressive sequence of carbonate ramp deposits. In central Mississippi, however, carbonate deposition was interrupted by a large influx of siliciclastic sediment derived from the ancestral Mississippi River. The Tchula Lake gas condensate field produces from dolomitic quartz arenite deposited in a mixed siliciclastic-carbonate environment. Several characteristics of the producing zone sandstone have led to reinterpretation as an eolian deposit that represents two coastal dune facies separated by a restricted lagoonal facies.

Reinterpretations are based on compositions and textures described in cores from the field. The first eolian facies consists of fine-grained, dolomitic quartz arenite, having mean porosities of 10-18%. The sand grains are rounded to subrounded and well sorted. Structurally, the sandstone exhibits a sequence of upward steepening dips of laminations capped at the top by a set of small-scale wedge planar crossbeds. This facies is interpreted as representing a backshore coastal dune. The restricted lagoonal facies consists of gray, bioturbated, dolomitic packstone with wispy, organic-rich partings, numerous burrows, and a low diversity fossil assemblage. The second eolian facies consists of fine to medium grained dolomitic quartz arenite, exhibiting mean porosities of 5-12%. The sand grains within each lamina are rounded and very well sorted. The sharply defined, parallel laminae are less than 5 mm thick and alternate between medium and fine sand without apparent grading. No fossils or trace fossils are found within this facies. The sandstone was deposited as low angle (<20-degree dip) climbing translatent strata produced through the migration and climb of wind ripples along a dune.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas