Print this pageA Proposed Basin-wide, Middle Smackover Lowstand and its Effect on Mixed Carbonate/Siliciclastic Facies and Carbonate Diagenesis in the Eastern Gulf Basin
BARIA, LAWRENCE R., EZAT HEYDARI, and MARK A. STEPHENSON
Widespread deposits of deeply brecciated, crusted, pisolitic, and recrystallized caliche occur across shallow portions of the Smackover sheff in the Mississippi Salt Basin and in the insular, updip reaches of Southwest Alabama. These exposure profiles are commonly overlain by Upper Smackover lime muds and shallow marine ooid shoals.
In the deeper, seaward areas of the basin margin, and within regional embayments, high resolution 3-D seismic delineates middle Smackover clastic sands with stratal geometries which cover tens of square kilometers and commonly measure 20 to 30 meters in thickness. Like their platform counterparts, these coeval sands are overlain by Upper Smackover subtidal and intertidal carbonates.
The widespread nature of both the exposure surfaces and the intrafomational clastics suggest either a lowering of sea level or tectonic uplift. When considered with similar features recently described in Louisiana, the Alabama and Mississippi occurrences support the idea of a regional eustatic fluxuation (LST) during Smackover deposition. Based on sequence geometries preceding and following this event, it appears likely that the observed lowstand would best correlate with a late Oxfordian (144 m a) boundary.
As a result of this middle Smackover event, a meteoric vadose style of diagenesis occurred in the updip, platform areas which significantly enhanced porosity and permeability. Much of the reservoir facies at Appleton, East Barnette, and Baileys Creek Fields may have developed during this time.
Because the lowstand clastic sands are sandwiched between rich source rocks of the lower Smackover and upper Smackover muds and sealing Buchner evaporites, these sands provide new and intriguing exploration targets to the Eastern Gulf Basin.