Conodont biostratigraphy of the Red House Formation (Middle Pennsylvanian) south-central New Mexico

The Red House Formation in south-central Sierra County, New Mexico preserves strata marking the onset of the inundation of shallow seas in southwestern North America during the Ancestral Rocky Mountain (ARM) orogeny. Early to Middle Pennsylvanian sediments were deposited within the newly formed orogenic basins and adjacent shelf regions. Grey, green, and black shales interbedded with fossiliferous limestones are the dominant lithotypes in the Red House Formation, and sandstone beds occur in the lower part. The Red House lithofacies likely represent a shallow marine shelf environment on the Robledo Shelf west of the Orogrande Basin. Samples were collected for conodonts at ten stratigraphic sections in the Mud Springs and Caballo Mountains, and the Derry and Rincon Hills. Abundant conodont elements occur intermittently in fine- to medium-grained carbonate packstone and grainstone beds and in packstone lenses in finer grained carbonates. Four successive conodont faunal intervals were recovered. A lower Red House faunal interval is characterized by Neognathodus species T, Declinognathodus marginodosus, Idiognathodus incurvus I, I. sinuosus, and Idiognathoides ouachitensis. A lower-middle Red House faunal interval can be distinguished by the presence of N. uralicus? The middle to upper Red House faunal interval is characterized by Neognathodus morphotypes transitional to N. bothrops and new species of Idiognathodus with similarities to Desmoinesian taxa. The uppermost Red House faunal interval is characterized by N. bothrops and Idiognathodus species H, in association with the fusulinid Beedeina, indicating that the top of the Red House is Desmoinesian in age, at least at some sections. The Red House Formation preserves a good, but discontinuous, record of Atokan conodont evolution in southwestern North America and provides new information for biostratigraphic correlation of Atokan strata and the Atokan/Desmoinesian boundary.