Lithofacies and Paleontology of Late Paleozoic Allochthonous Deep-Water Carbonates: Example from West Texas Subsurface: ABSTRACT

Abstract

Twenty-one lithologies have been identified in cores of lowermost Wolfcampian limestone and shale in six wells in Reagan and Crockett Counties in the general area of World field, Midland basin. These lithologies are summarized into four major lithofacies: (1) floatstone and variably compacted rudstone containing angular, lithologically diverse, platform-derived lithoclasts and bioclasts in a clayey or marly matrix; lithoclasts are a product of disintegration of lithified platform facies, probably Wolfcampian; (2) interbedded shale and thin, horizontal, and in places ripple-laminated, carbonate sands mainly of allochthonous bioclasts; (3) micritic rudstone and wackestone containing platform-derived micritic intraclasts and bioclasts; this facies is variably porous with int rgranular, moldic, solution-enlarged moldic, intragranular, and fracture porosity; (4) argillaceous packstone and wackestone with allochthonous bioclasts and intraclasts and semi-intraclasts of off-platform origin; this facies displays a variety of soft sediment deformation features. Facies components probably were supplied and emplaced episodically by a variety of shelf edge and slope processes during a time of faulting in the area. Syndepositional faulting is interpreted from thickening of strata on downthrown sides of faults. Rudite-size clasts were transported 15 mi (24 km) or more from the Central Basin platform to the west. Finer detritus swept basinward for much greater distances. Limited comparison is made with carbonate sediments of Exuma Sound, Bahamas. Off-platform Wolfcamp facies abruptly overlie and contrast strongly with a variety of Des Moines (Strawn) shallow subtidal platform facies displayed in three cores. The contact, present in one core, is interpreted primarily as a nondepositional disconformity. Age and facies determinations from the cores significantly alter correlations and interpretations made with wireline logs alone, resulting in improved exploration play concepts. Allochthonous carbonate complexes may well provide new, potentially important reservoirs in this region. End_of_Article - Last_Page 556------------