William C. Parcell¹, Ernest A. Mancini²

(1) University of Alabama, Tuscaloosa, AL
(2) The University of Alabama, Tuscaloosa, AL

ABSTRACT: Upper Jurassic Microbial Reef Outcrop Analogs for Smackover Reefs in the Eastern Gulf Coastal Plain

Upper Jurassic Smackover reef buildups in the eastern Gulf Coastal Plain are elongate features, 10 to 130 ft in thickness, consisting primarily of shallow-water, laminated (stromatolitic) and digitate and branching (thrombolitic) microbolites that develop on hardgrounds or rockgrounds associated with Paleozoic basement features. These microbial buildups are part of a catch-up carbonate system and are typically found associated with late transgressive to early highstand systems tracts deposits. Because these strata are not exposed at the surface in the eastern Gulf Coastal Plain, it is difficult to determine their geometries and extent for accurate petroleum reservoir characterization and modeling.

Upper Jurassic microbial buildups are exposed in Western Europe (France and Portugal) where they are associated with late transgressive to highstand systems tracts deposits depending primarily upon rate of sea-level rise and background sediment accumulation rate. In France, these microbial reefs have been observed in outcrop to consist of local, discontinuous stromatolitic to thrombolitic buildups that generally do not exceed 10 ft in thickness. However, in Portugal, microbial reefs consist principally of large thrombolitic buildups that attain thicknesses in excess of 100 ft. These reefs are associated with hardgrounds and occur in early highstand systems tract deposits.

Use of the Upper Jurassic microbial reef outcrops in Portugal to characterize and model the Smackover reefs in the eastern Gulf Coastal Plain has greatly facilitated the design of hydrocarbon exploration and development strategies for identifying and delineating Smackover microbial reef reservoirs through 3-D geologic and seismic modeling.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado