HEYDARI, EZAT, Basin Research Institute, Louisiana State University, Baton Rouge, LA; and W. C. DAWSON, T. C. O'HEARN, and H. M. SZYMCZYK, Texaco E & P Technology Department, Houston, TX

ABSTRACT: Patterns of Marine Diagenesis Related to late Jurassic Seawater Composition, Paleoceanography, and Paleoclimatic Conditions, Smackover Formation, Mississippi Salt Basin

The Smackover Formation exhibits two shoaling-upward cycles in the Mississippi salt basin. The lower cycle is composed of a lower lime mudstone lithofacies which grades upward into an ooid grainstone lithofacies. The upper cycle consists of a peloid packstone lithofacies which grades upward into an ooid grainstone lithofacies. In the lower cycle, basinward lime muds and ooids exhibit preserved original texture and low Sr, (isotope){18}O, and (isotope){13}C compositions; whereas landward lime muds and ooids show neomorphic texture and high Sr, (isotope){18}O, and (isotope){13}C values. In addition, the mudstones exhibit distinct vertical trends in (isotope){18}O and (isotope){13}C compositions. The ooids of the upper cycle exhibit preserved textures in both basinward and landward parts of the basin.

Petrographic and geochemical data suggest that during the deposition of the lower cycle, originally aragonite lime muds and ooids precipitated on the landward side while originally calcite lime muds and ooids formed on the basinward side of the basin. Precipitation of aragonite was the result of a shoreward increase in salinity, as indicated by (isotope){18}O compositions of lime muds and ooids. This salinity gradient was established by anti-estuarine circulation during a dry climatic period and persisted throughout the deposition of the lower cycle. Vertical variations in (isotope){18}O and (isotope){13}C compositions of mudstones of the lower cycle recorded fluctuations in sea-level, climate, and productivity cycles in the basin.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.