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KOPASKA-MERKEL, DAVID C., and STEVEN D. MANN, Geological Survey of Alabama, Tuscaloosa, AL

ABSTRACT: Upward-Shoaling Cycles in Smackover Carbonates of Southwest Alabama

Upper Smackover strata in Alabama commonly consist of one or more upward-shoaling cycles about 15 to 50 ft (3 to 16 m) in thickness. Multiple forcing functions (eustasy, regional tilting, salt halokinesis, and autogenic migration of facies) and varying water depths at the start and end of each upward-shoaling cycle generated an array of sedimentary responses. The Brittain No. 1 well, Permit No. 2478, Healing Springs field, Washington County, Alabama, illustrates nucleation of an offshore bar. Bar deposits are capped by anhydritic sabkha deposits, gradationally overlain by subtidal lagoonal strata. Varying rates (and directions?) of halokinesis controlled this succession. Locally varying rates of salt movement created as many as five sabkha-capped cycles in this area. The International Paper Company 20-5 No. 1 well, Permit No. 5242, Blacksher field, Baldwin County, Alabama, contains three upward-shoaling cycles capped by evaporites. Limited aggradational potential of supratidal evaporitic settings permitted subsidence-caused immersion, which eventually permitted reactivation of the carbonate factory and formation of the next cycle. The Chatom Unit 20-14 No. 1-04 well, Permit No. 7044, Chatom field, Washington County, contains three different cycles. The lower cycle consists of subtidal lime mudstone, capped by a 5-ft- (1.5-m-) thick soil zone that contains multiple exposure surfaces, tepee structures, and anhydrite pseudomorphs after lenticular gypsum crystals. The soil zone underlies an intraclastic storm deposit followed by a deepening-upward lagoonal succession. A t in ooid grainstone containing exposure surfaces caps the middle cycle. In the upper cycle, peritidal carbonate strata underlie sabkha deposits.

AAPG Search and Discovery Article #90989©1993 GCAGS and Gulf Coast SEPM 43rd Annual Meeting, Shreveport, Louisiana, October 20-22, 1993.