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The Darwin and Keeler Basins as Outcrop Analogs to the Permian Basin System


Over the last decade, the Permian Basin has risen to prominence as one of the richest petroleum accumulations in the world. The frenetic pace of exploration and development as well as the need for optimization of drilling and production has driven intense research efforts. One challenge facing this research is that Permian Basin oil-bearing strata are not exposed at the surface. The only way to directly study these rocks is through core, well-logs, or reflection seismic data. Each of these methods has major limitations because of cost, lateral continuity, and/or resolution. This challenge has been partly addressed through outcrop analogs, and rocks exposed in the Delaware and Guadalupe Mountains of West Texas have been used for this purpose. However, none of these exposures provides direct analog to Permian Basin subsurface rocks because (1) Guadalupe Mountains strata represent the shallow-marine depositional systems, (2) strata within the Delaware Mountains, although deposited in deep-water environments, are siliciclastic in composition, and (3) outcrops in the Delaware Mountains are privately owned, and access is difficult to impossible. Strata of the Darwin and Keeler Basins, located in Eastern California, provide direct outcrop analogs to subsurface rocks of the Midland and Delaware Basins. Here, we present preliminary results on the sedimentology and stratigraphy of Darwin and Keeler Basin strata. These systems are analogous in that they were both deposited (1) during middle Pennsylvanian to late Permian time, (2) at equatorial latitudes, (3) in calcic, deep-water turbidite-fan systems adjacent to shallow carbonate shelves, (4) and within a basin system that evolved from a single basin to two sub-basins separated by a shallow to emergent intra-basin uplift. Additionally, rocks in both basins are strikingly similar at the bed-scale: both systems were filled by thin-bedded sandy calc-turbidites in the distal portions of the basin, and both systems contain carbonate debrites and other coarse-grained sediment gravity-flow deposits proximal to the shelf edge. These bed-scale sedimentologic similarities suggest corresponding similarity in depositional processes. The results presented here suggest that the Darwin and Keeler Basins have high potential to improve our understanding of the Permian Basin system including sedimentary processes, basin evolution, and petrophysical character of calcic turbidite deposits.