Abstract: Geologic and Computer Modeling of Upper Jurassic Smackover Reef and Carbonate Shoal Lithofacies, Eastern Gulf Coastal Plain
MANCINI, E. A., H. CHEN, and D. J. BENSON
The
University of Alabama, Tuscaloosa, AL
Reefs and carbonate shoals have long been known from the Upper Jurassic
Smackover Formation in the Gulf Coastal Plain; however, these carbonate
lithofacies have unique acoustic properties that make them difficult to
define using 3-D seismic reflection technology. In the eastern Gulf Coastal
Plain, microbial reef and shoal buildups occur on pre-Jurassic paleotopographic
basement features on a carbonate ramp margin. Development of these buildups
is a result of the interplay among paleotopography, sea-level changes,
and carbonate productivity. Geologic and computer modeling indicates that
Smackover reef and shoal development is restricted to the flanks of high
(emergent) and intermediate (supratidal conditions) relief structures,
while reef and shoal development occurred on the crest and flanks of low-relief
structures (submergent). For these submergent features, modeling indicates
that carbonate productivity during reef growth was significantly greater
than during shoal development. In addition to the initial paleorelief,
the rate of sea-level rise, the level of carbonate productivity, and duration
of reef growth appear to be critical factors in determining thickness and
distribution of the reef lithofacies. Subsidence and compaction are minor
factors. Shoal development is greatly influenced by reef morphology, sea-level
changes, level of carbonate productivity, and duration of shoal development.
Subsidence, compaction and sediment redistribution are also factors. Modeling
of parameters affecting reef and shoal development associated with preJurassic
paleohighs in combination with 3-D seismic reflection studies increases
the chances of drilling a successful exploration well.
AAPG Search and Discovery Article #90932©1998 GCAGS/GCS-SEPM Meeting, Corpus Christi, Texas