A Conceptual Model for the Sequence Stratigraphy of the Smackover Formation in North-Central U.S. Gulf Coast
Ezat Heydari1 and Lawrence Baria2
1Department of Physics, Atmospheric Sciences, and General Science, P.O. Box 17660, Jackson, Mississippi 39217; [email protected]
2Jura-Search Inc., P.O. Box 997, Jackson, Mississippi 39205; [email protected]
Three sequences are recognized in the Smackover Formation in the north-central portion of the U.S. Gulf Coast (Mississippi, Louisiana, and Arkansas). In ascending order, they are here named the Smackover "C", the Smackover "B", and the Smackover "A" sequences.
The Norphlet Formation forms the lowstand systems tract of the "C" sequence. A rapid relative sea-level rise initiated the Smackover Formation part of the "C" sequence but left little to no transgressive systems tract deposits. Over 600 ft (183 m) of carbonates of the Smackover "C" sequence were deposited on a ramp and can be interpreted as a beach-to-basin prograding highstand systems tract to possibly a forced regression systems tract. The modern analog for the deposition of "C" sequence is the Persian Gulf.
The "C" sequence ramp was developed into a platform with a well-defined shelf margin. Continued relative sea-level fall exposed the "C" sequence carbonates to meteoric processes. Rivers extended to the shelf margin leading to deposition of sandstone turbidites in the basin forming the lowstand systems tract of the overlying Smackover "B" sequence. Again, the subsequent rapid sea-level rise left little to no transgressive systems tract deposits in the "B" sequence. Up to 600 feet (183 m) of wackestone-to-grainstone of the Smackover "B" sequence formed as prograding marine shoals along the shelf margin as highstand systems tract to forced regression systems tract showing well-developed clinoforms character on some seismic lines. Shoals ranged 20-80 m in height and 1-5 km in length. The modern analog to the "B" sequence is the marine sand belt system of the Bahamas.
The subsequence relative sea-level fall exposed the Smackover "B" sequence to subaerial processes. Adjacent to major rivers, sandstone turbidites were deposited in the basin forming the lowstand systems tract deposits of the overlying Smackover "A" sequence. The 70 foot-thick (21 m) wackestone-to-grainstones of the "A" sequence formed as isolated shoal along the shelf margin.
A relative sea-level fall at the end of the "A" sequence deposition exposed the Smackover platform to meteoric processes. The overlying Buckner sequence deposited as a transgressive systems tract during the subsequent sea-level rise forming a blanket of evaporite covering all three Smackover sequences. The Smackover and Buckner formations do not seem to be time equivalent in this model.
AAPG Search and Discovery Article #90080©2005 GCAGS 55th Annual Convention, New Orleans, Louisiana