CONODONT BIOSTRATIGRAPHY OF THE ATOKAN (PENNSYLVANIAN) RED HOUSE FORMATION, CENTRAL SIERRA COUNTY, NEW MEXICO

The Red House Formation in south-central Sierra County, New Mexico preserves strata marking the beginning of the Ancestral Rocky Mountain (ARM) orogeny in southwestern North America. Synorogenic early to middle Pennsylvanian marine sediments were deposited within the newly formed orogenic basins. 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 marine shelf environment. The Atokan fusulinid zones, the Profusulinella and Fusulinella zones, fall within the Red House Formation. 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. Conodont elements are more abundant in the lower limestone beds of the formation. Three successive conodont faunas were recovered. A lower Red House fauna is characterized by Neognathodus atokaensis, Declinognathodus marginodosus, Idiognathodus ssp. (sinuosus-klapperi-incurvus complex), Idiognathoides species., and rare Diplognathodus species. A middle Red House fauna can be distinguished by the appearance of Neognathodus sp.B and the loss of Declinognathodus. The upper Red House is characterized by Neognathodus bothrops and new species of Idiognathodus with similarities to Desmoinesian taxa, as well as the loss of Idiognathoides. The Red House Formation probably preserves the best record of Atokan conodont evolution in southwestern and Midcontinent North America and provides the basis for improved biostratigraphic correlation of Atokan strata. The presence of Diplognathodus orphanus and Neognathodus bothrops indicate that the base of the global Moscovian Stage, once it is defined, will lie within the Red House Formation.