Stratigraphy and correlation of the Permo-Carboniferous Cutler Group, Chama Basin, New Mexico
— Spencer G. Lucas and Karl Krainer

Nonmarine siliciclastic red beds at the base of the Phanerozoic section across most of the Chama Basin of northern New Mexico are assigned to the Pennsylvanian-Permian Cutler Group. These strata are here divided into two mappable lithostratigraphic units, the El Cobre Canyon and overlying Arroyo del Agua formations. The El Cobre Canyon Formation is up to 500 m of brown siltstone, sandstone and extraformational conglomerate of an ephemeral braided stream environment that overlies Proterozoic basement in the subsurface and is conformably overlain by the Arroyo del Agua Formation. Siltstone beds of the El Cobre Canyon Formation contain numerous rhizoliths and comprise relatively thin, slope-forming units between multistoried sandstone beds that are arkosic, micaceous, coarse grained and trough crossbedded. The Arroyo del Agua Formation is up to 120 m of orange siltstone, sandstone and minor intraformational and extraformational conglomerate of a braided to anastomosed stream depositional environment. The siltstones are thick, slope-forming units with abundant calcrete nodules between thin sandstone sheets that are arkosic and trough crossbedded. In the Chama Basin, the De Chelly Sandstone (= Meseta Blanca Member of the Yeso Formation) locally overlies the Arroyo del Agua Formation, but at most outcrops the Upper Triassic Chinle Group rests unconformably (some slight angularity is evident) on the Arroyo del Agua Formation. Megafossil plants, palynomorphs and fossil vertebrates indicate the El Cobre Canyon Formation is of Late Pennsylvanian-Early Permian (early Wolfcampian) age. Sparse fossil vertebrates indicate the Arroyo del Agua Formation is of late Wolfcampian age. Correlation of Cutler Group strata southward to Jemez Springs suggests that the Abo Formation is equivalent to the upper part of the El Cobre Canyon Formation and the entire Arroyo del Agua Formation. The lower part of the El Cobre Canyon Formation in the Chama Basin is correlative to mixed marine-nonmarine strata of the upper “Madera Group” at Jemez Springs.