ABSTRACT

Although associated with structural reversal and closure against a post-Smackover fault, hydrocarbon accumulation at Red Rock field in the upper members of the Late Jurassic Smackover and Buckner Formations is controlled for the most part stratigraphically by non-deposition or complete cementation of the reservoir facies. Red Rock is unique among the shelf-slope fields of Arkansas and Louisiana in that calcarenites of these members are productive on the downthrown side of a major fault. Petrographic study reveals no significant difference between calcarenites in downthrown and upthrown wells, and production may be expected from other areas which are now downthrown if they were favorably situated during deposition and diagenesis of the reservoir facies.

On the shelf slope, Smackover nonskeletal calcarenites were deposited as bars on shoals usually associated with slight structural uplift. Although Buckner calcarenites are similar to those of the Smackover, their geometry suggests a beach environment. A thick east-west bank of mixed facies was deposited regionally along the subsiding seaward edge of the shelf slope. Several transgressive units extend updip from this bank, and reservoir facies were deposited along the beaches, especially where high energy conditions persisted for considerable periods of time on positive features such as Red Rock. Between transgressions, lowering of sea level or lack of subsidence permitted southward progradation of evaporitic mudflats. Uplift of the continent caused seaward progradation of coarser clastics, and Buckner mudstone graded upward into nonmarine sandstone of the "P" tongue of the Schuler Formation. During deposition of the latter interval, maximum displacement occurred along a down-to-north fault.