Taphonomy of the Lower Permian Cardillo Quarry, Chama Basin, north-central New Mexico

The Lower Permian Cardillo quarry is located near Arroyo del Agua, in the Chama Basin in north-central New Mexico. The quarry is stratigraphically high in the El Cobre Canyon Formation of the Cutler Group, which is Wolfcampian in age. During excavations in 1979, 1980 and 2002-2004, the remains of the labyrinthodont amphibian Eryops, the diadectamorph Diadectes, a captorhinid reptile, a varanopseid pelycosaur, and the pelycosaurs Sphenacodon and Ophiacodon were recovered from the Cardillo quarry. Taphonomic analysis reveals that this locality is an attritional fossil assemblage. The bones lie within a series of three distinct, pedogenically modified conglomerates that also include calcrete nodules, chert, quartzite and other siliceous pebbles. The skeletal material is mostly disarticulated, though two partially articulated pelycosaur skeletons were recovered from overbank sediments above the uppermost conglomerate. Isolated skeletal elements and bone fragments are in various stages of weathering and abrasion. The assemblage was not hydraulically sorted because all three Voorhies groups are well represented. The Cardillo quarry assemblage was formed by a series of crevasse splays that incorporated bones, bone fragments and basement clasts (siliceous pebbles). Thus, it is a classic example of a time-averaged vertebrate fossil assemblage.