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Twenty-one lithologies have been identified in cores of lowermost Wolfcamp limestone and shale in 6 wells in the general area of World field, Midland basin. These lithologies are summarized into four major lithofacies. (1) One lithofacies is floatstone (greater than 10% clasts larger than 2 mm "floating" in finer matrix) and variably compacted rudstone (like floatstone, but grain supported) containing angular, lithologically diverse, platform-derived lithoclasts and bioclasts in a clayey or marly matrix. The lithoclasts are a product of disintegration of lithified platform facies, probably Wolfcampian. (2) A second facies is interbedded shale and thin, horizontal, and, in places, ripple-laminated carbonate sands mainly of allochthonous bioclasts. (3) Micritic rudstone and wackestone contain platform-derived micritic intraclasts and bioclasts. This facies is variably porous with intergranular, moldic, solution-enlarged moldic, intragranular, and fracture porosity. (4) Argillaceous packstone and wackestone with allochthonous bioclasts and intraclasts and semi-intraclasts are 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 active faulting in the area. Rudite-size clasts were transported 15 mi (22.5 km) or more from the Central Basin platform on 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 markedly with a variety of Desmoinesian (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 concepts. Allochthonous carbonate complexes may well provide new, potentially important, reservoirs in this region. Preliminary
pyrolysis analyses of shaly parts of the debris complexes suggest a good hydrocarbon source potential.
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