ABSTRACT

Upper Jurassic (Oxfordian) Smackover microbial reef buildups in the northeastern Gulf of Mexico consist primarily of shallow-water thrombolites that develop on hardgrounds or rockgrounds associated with Paleozoic basement paleohighs. These microbolites are typically associated with late transgressive to early highstand systems tract deposits and range from 10 ft (3 m) to 150 ft (45 m) in thickness. Because the Smackover strata are not exposed at the surface in this region, determination of the geometries and extent of these thrombolitic buildups, which are critical to devising hydrocarbon development strategies for these reservoirs, is difficult.

Upper Jurassic (Oxfordian and Kimmeridgian) microbial buildups are exposed in Western Europe where they are also associated with late transgressive to highstand systems tract deposits. In France, these microbial reefs have been observed in outcrop to consist of layered to dendroidal thrombolitic buildups that generally do not exceed 10 ft (3 m) in thickness. In Portugal, microbial reefs consist primarily of thrombolitic buildups that attain thicknesses of 100 ft (30 m). These buildups are associated with sediment starvation surfaces and hardgrounds and occur in early highstand systems tract deposits.

The use of Upper Jurassic microbial reef outcrops in Europe to characterize and model the Smackover thrombolitic reefs in the subsurface of the northeastern Gulf of Mexico greatly facilitates the design of hydrocarbon development strategies for delineating Smackover microbial reefs through 3-D geologic and seismic modeling.