Depositional Environments and Porosity Development, Strawn Formation (Middle Pennsylvanian), Wagon Wheel and HSA (Penn) Fields, West Texas

Darren L. McInturff, Rex C. Price, Robert F. Ward

The Wagon Wheel and HSA (Penn) fields are located on the western flank of the Central Basin platform within the Permian basin. In this area, both siliciclastic and carbonate depositional systems controlled sedimentation during Strawn time. To the east (HSA Penn field) siliciclastic fanglomerate sedimentation dominated. Several fanglomerate lobes, sourced from the Sand Hills uplift to the east, prograded westward across the platform. Interlobe swamps were common along this strand-line setting. Approximately 3 mi westward (Wagon Wheel Penn field), carbonate bank deposition dominated. Siliciclastic sands and clays commonly are intermixed within these carbonates and represent distal reaches of the siliciclastic progradational lobes. Conglomerates occur more rarely within the arbonate sequence.

Carbonates from the upper Strawn (HSA 1392-P well, Wagon Wheel Penn field) demonstrate five shallowing-upward sequences. Each sequence consists of a lower subtidal phylloid algal wackestone which shallows upward into a grainstone shoal deposited above effective wave base. Transgression was rapid and marked by the subtidal phylloid algal wackestone facies overlying the grainstone shoal facies at the top of the previous sequence. Where present, chaetetids punctuate the contact between sequences.

Variations between siliciclastic pulses, incorporated within the carbonate facies, also reflect the depositional setting. Fine-grained argillaceous material was incorporated within phylloid algal wackestone facies, whereas coarser silts and sands commonly were associated with shallower water carbonate shoals. Where present, the argillaceous material stifled algal production, and phylloid algal blades are rare.

Porosity occurs as interparticle voids within the nearshore fanglomerate lobes and as leached biomolds in the grainstone shoals of the carbonate bank. Phylloid algal-rich facies are tight. Porosity is adversely affected by clastic pulses within the grainstone shoal facies and by latestage ferroan calcite cement.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.