--> Abstract: Contrasting Transgressive Systems Tracts in Middle and Upper Jurassic Strata of Southwest Alabama, by W. J. Wade and C. H. Moore; #91012 (1992).

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ABSTRACT: Contrasting Transgressive Systems Tracts in Middle and Upper Jurassic Strata of Southwest Alabama

WADE, WILLIAM J., and CLYDE H. MOORE, Louisiana State University, Baton Rouge, LA

Contrasting lithologies and depositional styles are illustrated by three transgressive systems tracts (TST) within Middle and Upper Jurassic strata of southwest Alabama. In the first example, massive evaporites of the Bajocian-Callovian Werner Anhydrite and Louann Salt onlap Paleozoic rocks and graben-filling redbeds of the Late Triassic Eagle Mills Formation. Though poorly constrained by core or well data, the major portion of these units is interpreted to have been deposited during transgression in an extremely restricted basin.

In a second example, the uppermost portion of the Callovian Norphlet Formation lowstand systems tract is reworked by marine processes during Oxfordian transgression. In basinal areas, Norphlet tidal flat lithofacies are preserved at the base of the TST and are separated by a ravinement surface from overlying bioturbated marine sandstone. The subsequent abrupt transition into laminated and algal-laminated lime mudstones of the lower Smackover Formation was caused by cessation of siliciclastic influx resulting from continued relative sea level rise.

In the third example, the basal evaporite member of the Oxfordian Buckner Formation in Alabama includes thick halite (over 100 m) in basinal areas. It onlaps the Smackover Formation and is inferred to represent latest lowstand and subsequent TST deposition. In contrast, overlying parasequences of the late TST and HST of the upper Buckner and Haynesville formations are capped by thin veneers of sabkha anhydrite.

Accumulation of thick evaporites within the Werner/Louann and Buckner formations occurred during waning lowstand and subsequent TST deposition. These thick evaporites mark major turnarounds in relative sea level, under conditions of extreme restriction. Carbonate deposition within the lower Smackover TST is associated with moderate restriction of marine waters.

 

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)