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Sedimentology, Diagenesis, and Lithostratigraphy of the Desmoinesian Upper Fort Scott, Labette Shale, and Lower Pawnee Limestone Formations (Marmaton Group) in Eastern Colorado

Andrew Eck and Sal Mazzullo

Regional gamma ray log cross-sections incorporating outcrop gamma measurements from eastern Kansas aid in delineating Desmoinesian stratigraphy in eastern Colorado and western Kansas by tracing highly radioactive, regionally invariable shale units. A representative type log of the upper Cherokee and Marmaton Groups in eastern Colorado presents the correction of local stratigraphic nomenclature. Sixty-three feet of core (from SE Colorado) in the Higginsville Limestone Member of the Fort Scott Formation upward through the Myrick Station Limestone Member of the Pawnee Formation were studied to determine sedimentological and diagenetic controls on reservoir development. Higginsville rocks are composed of subtidal to peritidal lime mudstone cycles overlain by a peloidal grainstone reservoir. Original porosity was occluded by calcite and later dolomite cements, precipitated from fluids moving through fracture systems. Secondary porosity was later created by mesogenetic dissolution proximal to stylolites and fractures. Rapid eustatic drowning caused the deposition of the Labette Shale Formation and the overlying Anna Shale Member of the Pawnee Formation. Carbonate turbidites in the Anna Shale were sourced by higher-energy facies along the Las Animas Arch. Myrick Station rocks are low-energy phylloid algal wackestones overlain by a Chaetetes reef. A combination of subsurface mapping and well log analysis is sufficient to predict reservoir facies in the Myrick Station Limestone. However, mesogenetic dissolution porosity such as that found in the Higginsville Limestone often proves impossible to predict with satisfactory success.

AAPG Search and Discovery Article #90176©AAPG Mid-Continent Meeting, Wichita, Kansas, October 12-15, 2013