Abstract

The major lithologic subdivisions of the "Wolfcamp" strata in the western part of the Delaware basin are described. Also presented is the probable stratigraphic relationship of these strata to equivalent beds present on the Northwestern shelf and in outcrops to the northwest and west.

The term "Wolfcamp" is used as an operational unit and may contain some beds slightly older and/or younger than the lower Permian Wolfcamp Series. The top of the "Wolfcamp" in the basin is the top of the "3rd Bone Spring Sand" (or Dean) — a regional subsurface marker within the western Delaware basin. On the adjacent platform the "Wolfcamp" is bounded on the top by the Drinkard Sandy Member of the Yeso Formation-a regional subsurface marker on the Northwestern shelf. The base of the "Wolfcamp" commonly is defined by a regional unconformity which overlies rocks ranging in age from Late Pennsylvanian to Precambrian.

"Wolfcamp" strata in the western Delaware basin locally exceed 6000 feet in thickness and are among the least wellknown sequences in the basin. These strata are generally dark colored and the carbonates are generally lime packstones, wackestones, and mudstones. The "basinal Wolfcamp" can be subdivided into (1) a lower detrital unit which is quite variable in thickness and lithology, (2) a middle sequence of lime-shale-lime which is somewhat more uniform in thickness and lithology, and (3) the "3rd Bone Spring Sand" which is quite uniform in thickness and lithology. All of these units probably were deposited in a basinal (relatively deep water) environment. Deposits of the lower detrital unit range from conglomerate to feldspathic sandstone to shale and tended to level out the irregular basin floor topography created by Late Pennsylvanian-Early Permian tectonism. Taken as a whole, the "basinal Wolfcamp" records a transition from a period of active tectonism to one of relative stability.

In contrast, "Wolfcamp" strata on the Northwestern shelf are generally light colored, the carbonates are commonly dolostone, and most of the rocks have grain-supported textures. The "shelf Wolfcamp" strata were probably deposited in environments ranging from nonmarine to shallow water marine. The "shelf Wolfcamp" can be subdivided into (1) a lower clastic unit which locally exceeds 2,000 feet in thickness north of the Huapache fault zone, (2) the Abo-Hueco Formations, a thick carbonate tongue grading northwestward into Abo red beds, (3) the lower carbonate-evaporite member of the Yeso Formation, and (4) the Drinkard Sandy Member of the Yeso Formation.

Correlation between "basinal Wolfcamp" and "shelf Wolfcamp" sequences is difficult. Details of the stratigraphic relationships in these sequences are complex and as yet poorly understood. The lower clastic unit of the "shelf Wolfcamp" is similar in age and closely resembles, in lithologic variation (red beds to clean carbonates) and tectonic setting, the Laborcita Formation in the northern Sacramento Mountains. The Abo-Hueco carbonate tongue represents a major marine transgressive-regressive cycle. The lower member of the Yeso represents a similar cycle which terminated in the deposition of the Drinkard. The Drinkard Sandy Member is believed to represent the remnant of great quantities of very fine sand and silt which were transported across the Northwestern shelf to the Delaware basin where it accumulated as the 3rd Bone Spring Sand.