290-11 Comparative analysis of Pennsylvanian (Desmoinesian) Mixed Carbonate-Siliciclastic Subsurface Deposits of the Strawn Group, Permian Basin, Texas and an Outcrop Analog in the Bug Scuffle Member, Sacramento Mountains, New Mexico

Session: Delta Evolution from Rivers to the Shelf: Past, Present and Future Perspectives for Society

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Abstract:

The Desmoinesian Strawn Group found along the Eastern Shelf of the Permian Basin, north-central Texas, contains prolific oil and gas reservoirs that have produced for 100 years. The Strawn contains mixed carbonate-siliciclastic deposits that record complex relationships between deltaic point sources, a tidally-dominated shelf, and a carbonate ramp. While deposits of contemporaneous carbonate-siliciclastic systems are common, they remain rarely studied and their depositional controls are poorly understood. Because Strawn outcrops are sparse, spatial-temporal analysis of Strawn depositional system evolution relies primarily on subsurface data sets including sporadic core, localized wireline logs, and isolated seismic reflection profiles. This has been a significant barrier to developing comprehensive depositional models of the Strawn.

Our goal is to build on and enhance models of mixed carbonate-siliciclastic depositional systems to improve predictability for Strawn reservoirs. We describe facies stacking patterns and identify key sequence stratigraphic surfaces across numerous cored wells in Upper Strawn strata from Stonewall-King counties, Texas. Significant facies include crinoid-skeletal grainstones, trough cross-stratified fossiliferous sandstones, heterolithic wavy and lenticular bedded mudstone and interbedded fine sandstones, herringbone cross-stratified sandstones, and heavily bioturbated sandstones. We provide evidence for both along depositional strike and up-dip to down-dip changes in depositional settings to reconstruct the paleoenvironmental evolution of the Strawn mixed system.     

We also investigated an outcrop analog for Strawn reservoirs in mixed carbonate-siliciclastic deposits of the Bug Scuffle Member of the Gobbler Fm in the Sacramento Mountains of New Mexico. Bug Scuffle facies are strikingly similar to Strawn facies; however, outcrops allow us to examine extensive lateral exposures of stratal architectures. Interpreted paleoenvironments in both the Strawn subsurface data and Bug Scuffle outcrop analogs include channels, interdistributary bays, delta mouth bars, delta front, prodelta, skeletal-oolitic shoals, and various subtidal carbonates deposited along a ramp profile. The interfingering of carbonates and siliciclastics in both subsurface and outcrop data suggest that allogenic processes such as high frequency, high amplitude sea level fluctuations during the Pennsylvanian icehouse, the location of major siliciclastic fairways, and autogenic processes such as delta lobe switching, fluctuating freshwater input, and tidal modification are responsible for the internal characteristics of both the Strawn and Bug Scuffle deposits. Improved understanding of controls on mixed carbonate-siliciclastic depositional environments from core and outcrop analogs will help predict three-dimensional heterogeneity in Strawn reservoirs.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7153

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