Journal of Earth Science ( IF 2.209 ) Pub Date : 2021-02-22 , DOI: 10.1007/s12583-020-1392-9 Martyn Lee Golding
The Olenekian-Anisian Boundary (OAB) interval is an important time in Earth history, reflecting the last phase of marine ecosystem recovery in the aftermath of the end-Permian mass extinction. Despite this, the Global Stratotype Section and Point (GSSP) for the base of the Anisian remains undefined. The first appearance of the conodont Chiosella timorensis has been proposed as a potential index for the boundary; however, the discovery of this conodont with ammonoids traditionally considered to be Spathian has generated doubts about its suitability. The taxonomy and relationships of early Anisian conodonts, including species of Chiosella, remain understudied, which leads to difficulties in correlation. New species of Neogondolella (N. gradinarui) and Magnigondolella (M. n. sp. D) have been recognized from the leading GSSP candidate section for the OAB at Deşli Caira, and from an additional OAB section at Guandao. Furthermore, several species previously identified in Canada and the USA can be recognized from these sections, improving correlation between Tethys and North America. One of these species may serve as a suitable alternative proxy for the OAB; for instance, N. curva appears just below the first Anisian ammonoids in Deşli Caira, and just above the first appearance of C. timorensis in both Deşli Caira and Guandao. Continued work on sections other than the candidate sections, and on the taxonomy of species outside of those traditionally proposed as indices, is required.