Lithofacies of the Pennsylvanian Osha Canyon Formation at the type section, Jemez Mountains, New Mexico

The Pennsylvanian Osha Canyon Formation at the type section in the Jemez Mountains (northern New Mexico) is a 27.3-m thick succession composed of fossiliferous marly shale with intercalated limestone beds and a mixed  siliciclasticcarbonate sandstone bed on top. Limestone is represented by bioclastic grainstone, locally grading into packstone. The mixed siliciclastic-carbonate sandstone forming the uppermost part of the section contains up to 20% skeletal grains. Sediments of the Osha Canyon Formation were deposited in a shallow-marine shelf environment with normal salinity. Fossiliferous marly shales indicate low-energy conditions below wave base; intercalated limestone beds and sandstone on top were deposited under highenergy conditions above wave base. Deposition of the Osha Canyon Formation occurred during a period of relative tectonic quiescence with some weak tectonic pulses, which probably caused minor sea-level changes. Increased siliciclastic influx in the upper part of the Osha Canyon Formation points to increased tectonic activity.