Reynolds Oolite of Southern Arkansas

Abstract

The Jurassic Reynolds oolite is the upper member of the Jurassic Smackover Formation in southern Arkansas. This carbonate unit is widespread, relatively uniform in thickness, and has definite patterns of regional and local lithic changes. The patterns are analogous with those of carbonate sediments now being deposited in the Bahama Islands. Lithically, the Reynolds and Bahamian oolites are similar. In southern Arkansas the Reynolds oolite member is shown to contain five facies: (1) calcarenite-carbonate mudstone facies composed of fine-grained to silt-size carbonate particles in a microcrystalline (carbonate mud) matrix; (2) interbedded facies characterized by a predominance of calcilutite interbedded with lesser amounts of oolitic limestone; (3) grapestone facies compose of pellets and oolites aggregated or encrusted into lumps resembling bunches of grapes, in a matrix of calcarenite-carbonate mudstone; (4) modified grapestone facies composed of essentially the same rocks as the grapestone facies but with a pitted or honeycombed appearance resulting from solution of the oolites and pellets; and (5) oolite facies composed predominantly of oolites and pisolites of various sizes cemented by crystalline calcite. The Buckner Formation overlies the Smackover Formation and is largely evaporitic and nonmarine. Lateral changes in Buckner lithology parallel facies changes in the Reynolds oolite member.