Paper No. 9
Presentation Time: 9:00 AM-6:30 PM


LUCAS, Spencer G., New Mexico Museum of Natural History and Science, 1801 Mountain Road N.W, Albuquerque, NM 87104,

In 1998, the base of the Permian was defined by the FO (first occurrence) of the conodont Streptognathodus isolatus at the GSSP located at Aidaralash Creek in western Kazakstan. However, it is now clear that (1) S. isolatus is extremely rare— globally, there are only 3 well-documented records and a handful of undocumented reports; (2) with respect to fusulinid biostratigraphy, the FO of S. isolatus is diachronous, and (3) the taxonomy and evolution of S. isolatus are not agreed on. This calls into question the conodont-based definition of the base of the Permian. In North America, the base of the Permian had been identified as the base of the Wolfcampian Series since ~1939, based on the FO of Schwagerina in the North American sense. However, longstanding and widely accepted fusulinid correlations indicate that the conodont-defined Permian base at the Aidaralash GSSP is younger than the Wolfcampian base, and corresponds closely to the early-middle Wolfcampian boundary. This has created much confusion with respect to the base of the Permian in North America, particularly with regard to a vast literature developed for an oil industry understanding of the greater Permian basin. It also fueled an unnecessary debate over whether a new stage, “Bursumian,” was needed in the North American provincial chronostratigraphy to equal early Wolfcampian time, so that the system boundary would not be within a provincial “stage,” but correspond to a “stage” boundary. Instead, we need to reconsider the position of the base of the Permian and its current GSSP, and reposition the base of the Permian so as to respect longstanding usage and produce the most correlateable boundary. The current, conodont-based definition does not meet these criteria, but a fusulinid-based definition does. Two choices are available--the LO of North American Schwagerina s. str., which defines the base of the Wolfcampian, or the LO of an inflated schwagerinid taxon, which defines the beginning of the middle Wolfcampian and is closer to the original base of the Asselian. I favor the FO of North American Schwagerina because it is highly correlateable, marks a major biological event—the beginning of the explosive diversification of schwagerinids--and retains longstanding and extensive North American usage that equates the base of the Wolfcampian with the base of the Permian.