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Catherine O'Hara Merriam1, Steven L. Dorobek2
(1) Texaco Worldwide Exploration and Production, New Orleans, LA
(2) Texas A&M University, College Station, TX

Abstract: Lower Permian Carbonate Buildups in the SW Midland Basin, Texas: Buildup Growth Histories, Subtle Seafloor Bathymetry and Effects on Gravity-flow Sedimentation

An extensive 3-D seismic and well-log data set was used to analyze Lower Permian carbonate buildups in the SW Midland Basin, Texas. The buildups are located east of the Central Basin Platform (CBP) and formed just after major uplift of the CBP, while the Midland Basin was rapidly subsiding.

The buildups are found in the middle to upper Wolfcampian Eddleman and lower-middle Leonardian Amacker formations (informal units), which consist of skeletal limestone, matrix-supported limestone, lithoclastic facies, and minor boundstone facies. Carbonate deposition began during lowstands, within or just below wave base. Transgressive, dark-colored calcareous shale of the Twenty-one formation (upper Wolfcampian) terminated Eddleman carbonate sedimentation, although Amacker buildups resumed during ensuing lowstand. Amacker buildups were terminated in middle Leonardian time when transgressive, dark-colored mudrocks of the Tippett shale were deposited.

Subtle paleobathymetric features along the Early Permian ramp were created by post-Strawn (middle Pennsylvanian) deformation. Buildups are identifiable as subtle ‘thicks’ on 3D seismic data and consist of either skeletal-sand or lithoclastic debris. Skeletal-sand buildups began growth in paleolows and once they created synoptic relief, they caused sediment gravity-flows to move between them. As on outer parts of ramps throughout the rock record, these buildups indicate how subtle structural and depositional features can influence buildup locations, growth histories, and dispersal paths of sediment gravity-flows.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana