New Mexico Geological Society Annual Spring Meeting — Abstracts

A remarkable Early Permian (Seymouran, Wolfcampian) bonebed (New Mexico Museum of Natural History locality 5379) in the upper part of the Arroyo del Agua Formation in Cañon del Cobre, north-central New Mexico, yields principally Sphenacodon ferox material. This bonebed is in poorly sorted (vfL to cL), immature, arkosic, slightly laminated, dark reddish brown sandstone with pale greenish yellow color banding at ~ 10 cm intervals. Elongate bones generally trend ~ N30E with loose alignment (~ +/- 35º ), and in situ rhizoliths are common. A single articulated skull was present. The bones represent all three Voorhies Groups, but disarticulated skull and mandible material account for the greatest portion, especially when the original proportions of bone types is considered (i.e. there should be ~ 50 vertebrae per skull if unsorted).

A preponderance of Voorhies Group III material would indicate a heavily winnowed or a lag deposit, but much of the skull material is disarticulated into relatively flat bones that probably belong to Group I. Both the finely laminated rock and the Voorhies Group abundances indicate a floodplain deposit. Loosely aligned bones with incomplete sorting point to a relatively gentle flow. The Cañon del Cobre Sphenacodon bonebed probably accumulated on a floodplain with periodic (possibly annual), low-velocity sheet floods that hydraulically sorted the bones. More data will be acquired to refine the analysis.