Sedimentology of Guadalupian deep-water clastic facies, Delaware Basin, New Mexico and Texas
— Charles R. Williamson

The Delaware Mountain Group is a 1000- to 1600-m thick section of siltstone and sandstone that was deposited in the deep-water Permian Basin. Sandstones of the Delaware Mountain Group are the principle reservoirs in more than 100 oil and gas fields, and fine-grained, highly organic siltstones interbedded with the sandstones are considered to be source rock facies for oil in Delaware Basin reservoirs (Collins, 1975). Excellent outcrops along the western edge of the basin and abundant subsurface data provide an opportunity to study the facies distribution, sandstone geometry and reservoir properties of deep-water clastic sediments in a structurally undeformed setting. This paper summarizes outcrop and subsurface studies of the Bell Canyon Formation, the uppermost member of the Delaware Mountain Group. A more complete discussion of the results presented here can be found in Williamson (1978, 1979). Many of the same observations and interpretations are equally applicable to other members of the Delaware Mountain Group (Harms, 1974; Payne, 1976; Bozanich, 1979).

The deep-water depositional setting of the Delaware Mountain Group is well established by stratigraphic relations with timeequivalent shelf and shelf-margin rocks and has led many workers to suggest that sediments of the Delaware Mountain Group were deposited by turbidity currents (Newell and others, 1953; Hull, 1957; Silver and Todd, 1969; Meissner, 1972; Berg, 1979). A submarine fan depositional model for the Delaware Mountain Group proposed by Jacka and others (1968) commonly is cited as an example of deep-sea sedimentation in an intracratonic basin. However, results of this study indicate that most sand in the Bell Canyon Formation was deposited in nonbranching, nearly parallel submarine channels oriented at high angles to the shelf margin with no discernible fan morphology. The channels were cut by bottomhugging, clay-free density currents and filled by sand and silt in a complex, unordered manner, similar to that described by Harms (1968, 1974) from his study of outcrops of the slightly older Brushy Canyon Formation. Laminated, highly organic siltstone was deposited as a suspension blanket and occurs in channels and interchannel areas. The sandstone-filled channels are up to 8 km wide, 35 m deep and extend more than 70 km basinward. The channels set up numerous stratigraphic traps against regional monoclinal dip as a result of the pinchout of channel sandstone into less permeable interchannel siltstone.