The unique preservational environment of the Early Permian (Cisuralian) fossiliferous cave deposits of the Richards Spur locality, Oklahoma

Abstract

The Richards Spur locality, Oklahoma, USA, represents an Early Permian infill in a series of Ordovician limestone and dolostone karst fissures. It exhibits the most diverse terrestrial Palaeozoic community currently known, with >40 distinct tetrapod taxa. Speleothems intimately associated with the site indicate that Richards Spur is a cave system, suggesting a preservational environment that is distinct from those of more typical Early Permian lowland deltaic/fluvial localities. Fossil material obtained from the caves is often found in disarticulation, although articulated material is not uncommon. This suggests that there were several factors that affected how animal remains became deposited within the caves. Many animals that died outside the caves were likely disarticulated on the surface and then washed in during rainfall events, resulting in mostly disarticulated remains. Alternatively, animals could be washed in before being disarticulated and some probably fell into the caves, resulting in less chance for their remains to become disarticulated. Supporting evidence for these preservational hypotheses comes in the form of wear caused by attritional processes. Disarticulated elements can exhibit high levels of wear, likely due to water transport that would carry them into the caves from the surface, as well as reworking within the caves. The partially and completely articulated remains are normally unworn, presumably due to a lesser degree of transport and reworking. X-ray diffraction and stable isotope analysis of cave infill further supports the interpretations made from fossil material. The results of this study provide a much-improved understanding of the preservational environment at Richards Spur, and will be useful in integrating information from this unique upland locality with that from the more extensively studied lowland localities of the Early Permian.