Stratigraphic Investigations of the Wolfcamp Group in Core, Outcrop, and Well Logs in the Permian Basin of West Texas
Abstract
The Lower Permian Wolfcamp Group in the West Texas Permian Basin is recognized as an economically significant unit that has extremely complex stratigraphy. These deposits were historically well studied only in isolated regions where data was abundant, as is the case on the highly developed Eastern Shelf of Midland Basin (a sub-region of the Greater Permian Basin) or in outcrop exposures. More recently, data has become abundant in the basinal occurrences of the Wolfcamp Group, first in Midland Basin and then in Delaware Basin. This work integrates a variety of data sets to delineate the regional stratigraphy of the Wolfcamp Group in multiple settings across the Permian Basin.
First, two extended (>1000’ thick) cores through the Wolfcamp Group in Southern Midland Basin and their XRF-derived chemofacies are interpreted through a novel stratigraphic model which posits that siliceous deposition and carbonate deposition can, under certain conditions, reflect highstand and lowstand conditions, respectively. This differs from the implementation of the traditional reciprocal-sedimentation model, which often assumes that significant detrital sediment is available, and that inherited topographies are such that shallow (photic zone) carbonate factories have reduced surface area during sea level lowstands.
Second, proximal deposits in the Wolf Camp Hills type-locality outcrops were studied using traditional stratigraphic techniques combined with drone photogrammetry and handheld gamma-ray spectroscopy to document two large-scale (3rd -order) sequences occurring in the Lower Wolfcamp Formation. These sequences are bounded by unconformities and associated carbonate-clast conglomerate deposition and create a framework into which chemostratigraphic data are placed.
Third, available well log data is used to correlate chronostratigraphic surfaces in the Wolfcamp Group from the tectonically complex and understudied Southern Delaware Basin near the type section outcrops to the Southern Midland Basin (west-east correlations) and to the central Delaware Basin (south-north correlations). These correlations create a chronostratigraphic framework into which absolute age dates can be extrapolated with confidence across the Greater Permian Basin.
In summary, the results of these studies reinforce the complex nature of Wolfcamp Group stratigraphy, which varies dramatically as a function of its position within the Greater Permian Basin. Specifically, distal, basin floor strata contain thick and complex lowstand sedimentary packages, sometimes carbonate-rich, which are expressed as unconformities overlain by carbonate-clast conglomerates in proximal strata. Conversely, transgressive and highstand system tracts result in the deposition of highly radioactive (>100 API units) mudstone intervals, often siliceous in composition, which are apparent on well logs and can be correlated regionally, including from the basin center onto the Southern Shelf. These correlated surfaces connect studied cores in Southern Midland Basin with the outcrops in Southern Delaware Basin, and provide a unifying framework for the Wolfcamp Group in the Greater Permian Basin.
Citation
Richards, Benjamin Henry (2021). Stratigraphic Investigations of the Wolfcamp Group in Core, Outcrop, and Well Logs in the Permian Basin of West Texas. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /196324.