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Provenance and Depositional Controls on Reservoir Quality of the Lower Permian (Leonardian) Spraberry Formation, Midland Basin, TX


Sediment source areas and drainage networks control sediment supply to basin margins and basinal detrital mineral composition, all of which influence oil and gas reservoir presence and quality. The Lower Permian (Leonardian) Spraberry Formation in the Midland Basin, West Texas, comprises 1,000-2,500 feet of deep-water strata. Previous studies have largely interpreted that the primary siliciclastic sediment inputs to the Permian Basin were from the Ancestral Rocky Mountains (ARM) and/or the Appalachian mountain belt through fluvial and eolian systems. Here we present new detrital zircon U-Pb ages (929 grains from seven samples) and point-counts (1400 points) of framework grain composition and texture in the seven samples from the Spraberry Formation in a continuous drill core (~300 m) to investigate the evolution of Leonardian sediment dispersal in the southern North American margin. Spraberry strata include grain age populations from peri-Gondwanan (500- 310 Ma), Pan-African/Rodinian (750- 500 Ma), and Grenvillian (1315- 950 Ma) provinces, with minor contributions from Granite-Rhyolite (1585- 1300 Ma), Yavapai-Mazatzal (1800- 1600 Ma), and Archean ( > 2.5 Ga) provinces. Zircon core-rim ages and petrographic analysis suggest significant siliciclastic sediment delivery from a southern hinterland related to the Marathon-Ouachita orogeny. Through the integration of the new and published results from Permian strata in the ARM intraforeland basins, and basins adjacent to the Appalachian-Ouachita orogenic belts, we hypothesize that the Midland Basin has been primarily supplied by adjacent mountainous source areas, rather than previous interpreted long-distance rivers emanating from the ARM and Appalachian mountain belts. Sediment sources, process-controlled facies distribution, and reservoir properties are compared to further assess the controls of provenance and depositional processes on reservoir quality. These results (1) inform understanding of how sediment and environmental signals are transferred from source to sink in a globally significant type of sediment-routing system: large drainage basins connected to upstream high-relief mountain belts, and (2) allow for a more accurate prediction of reservoir quality in this type of system by understanding the relative proportion of bedrock contribution.