Carbonate Gravity-Flow Sedimentation on Low-Angle Slopes off the Wolfcampian Northwest Shelf of the Delaware Basin
R. G. Loucks, A. A. Brown, C. W. Achauer, D. A. Budd, 1985. "Carbonate Gravity-Flow Sedimentation on Low-Angle Slopes off the Wolfcampian Northwest Shelf of the Delaware Basin", Deep-Water Carbonates: Buildups, Turbidites, Debris Flows and Chalks—A Core Workshop, Paul D. Crevello, Paul M. Harris
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Wolfcampian gravity-flow deposits accumulated in a slope to basinal setting between shelf-edge Tubiphytes reefs on the Northwest shelf and calcareous mudstones of the deeper Delaware basin. These gravity-flow deposits are well displayed in a 25 meter long core from the Depco Inc. No. 1 D.H.Y. State “A” well drilled in Eddy County, New Mexico.
Ten depositional units have been delineated from core examination. Seventy-five percent of the cored interval is of debris-flow origin and consists mainly of orthoconglomerates with calcareous siliciclastic mudstone matrix. The remainder of the section consists of turbidite deposits of lime packstones, lime grainstones, and siliciclastic muddy siltstones and suspension deposits of calcareous silicilastic mudstones. The gravity-flow processes were operative on relatively low-angle slopes ranging from less than 1 degree up to 3-5 degrees and off a platform of relatively low relief (220 m). The low relief and low-slope angles were enough to initiate and sustain transport of blocks several meters in diameter for distances over 14.5 km.
Transport of large lithoclasts of wackestones, packstones, and grainstones indicates early lithification of these rocks probably by meteoric diagenesis. Later subsurface diagenesis resulted in cementation by saddle dolomite and Fe-rich, coarse-crystalline calcite. The larger lime boundstone blocks contain moldic and intraparticle porosity and a few of the grainstone clasts contain interparticle and moldic porosity inherited from the source area on the shelf. The porosity network in the Depco core consists of these porous limestone clasts and blocks separated by nonporous calcareous siliciclastic mudstone. This arrangement of blocks and matrix results in a poor reservoir because there is no porosity collection network, such as fractures.
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Deep-water carbonates represent on the few frontiers remaining for carbonate exploration and research. The last decade has experienced a rapid evolution in concepts of depositional models and diagenesis which underscores the importance of these deposits as significant reservoirs and source rocks. This workshop displayed cores selected to provide subsurface geologic examples of deepwater carbonates from a variety of depositional settings. Several papers discuss depositional models, platform-to-basin reconstructions, and diagenetic sequences that are important in the development and exploration of Paleozoic carbonate debris flow and turbidite reservoirs of the Palo Duro, Delaware and Midland Basins. Many other examples are included from several different regions.