Wolfcampian carbonate platform sequence stratigraphy of the southwestern Delaware Basin : Wylie Mountains, Van Horn, TX

The Wolfcamp unconventional play in the Permian Basin is currently one of the most active drilling targets in North America. Despite its economic importance, the Early Permian Wolfcampian interval in the Delaware Basin lacks a detailed understanding of the linkage between carbonate platform sedimentation and basinal deposits. Previous studies on Wolfcampian platform carbonates in the Permian Basin and Orogrande Basin from outcrop and subsurface work have interpreted variable sequence frameworks, which suggests antecedent topography, local to regional tectonic activity, and/or other localized depositional controls likely have significant influence on sequence architecture. This study presents a stratigraphic framework from the Hueco Formation in the Wylie Mountains near Van Horn, Texas that records middle to late Wolfcampian deposition in the southwestern Delaware Basin. These inner ramp carbonate strata correlate with outer ramp to basinal deposits to the northwest in the Sierra Diablo Mountains on the western shelf of the Delaware Basin. This combined data set allows for the recognition of both eustatic and tectonic controls on carbonate platform sequence architecture during the Wolfcampian. Eleven partial measured stratigraphic sections totaling 1450 m were used to generate a 300 m composite section for the Hueco Formation exposed in the Wylie Mountains, which records middle to late Wolfcampian carbonate sedimentation overlying the early to middle Wolfcampian Powwow Formation siliciclastics. Nine depositional facies are recognized from field observations and petrographic analysis. These facies are grouped into four depositional facies tracts, including outer ramp, low energy inner ramp, high energy inner ramp, and tidal flat facies tracts. Three sequences were interpreted based on 1D and 3D facies and cycle stacking pattern analysis, including two middle Wolfcampian sequences and one late Wolfcampian sequence. The late Wolfcampian sequence backsteps relative to the middle Wolfcampian sequences, consistent with observations of Hueco Formation sequence architectures in outcrop around the Diablo Platform and in the subsurface. The top of the Hueco Formation in the Wylie Mountains is bounded by an unconformity caused by a relative sea level of fall of at least 40-45 m at the end of the Wolfcampian which was succeeded by an influx of siliciclastics in the early Leonardian. Additionally, extensive brecciation and deformation have been documented in the lower two sequences. This deformation is interpreted to be related to dissolution of interbedded evaporites associated with tidal flat deposition in the upper portion of the lowermost sequence. Structural data suggests that late Wolfcampian tectonism may also have influenced deformation in this stratigraphic interval. The primary contribution of this study is improved resolution of Wolfcampian platform sequence stratigraphy and relative sea level change in the southwestern Delaware Basin. Identifying periods of sea level lowstand in the platform record is important because these periods are often associated with siliciclastic bypass of the shelf and increased sedimentation to the basin. Due to the generally low porosity and permeability of the basinal Wolfcamp Formation, these bypass events are critical for the development of coarse grained or siliciclastic sand rich units that can serve as highly productive Wolfcamp oil and gas reservoirs. The end-Wolfcampian sea level fall and associated conglomeratic unit documented in this study at the top of the Hueco Formation suggests a period of siliciclastic bypass in the earliest Leonardian in the southwestern Delaware Basin.Geological Science