Ammonoid stratigraphy and sedimentary evolution across the Permian–Triassic boundary in East Greenland

Abstract

East Greenland is a classical area for the study of the Permian–Triassic transition and the succession is one of the most expanded in the world. New ammonoid data from the Wordie Creek Formation have allowed us to better reconstruct the history of the East Greenland basin from semi-isolated basins with an endemic fauna during latest Permian–earliest Triassic H. triviale–H. martini zones time to well-connected open marine shelf basins during the Early Triassic M. subdemissum, O. commune, W. decipiens and B. rosenkrantzi Zone times. The East Greenland zonation can be correlated with Boreal zonations in Arctic Canada, Svalbard and northeastern Asia. It allows precise relative dating and correlation of important events across the Permian–Triassic boundary. The new ammonoid data indicate that deposition was continuous across the Permian–Triassic boundary and developed as a marine mudstone–mudstone contact in basinal areas of Hold With Hope, northern and southern Jameson Land. Correlation of the ammonoid stratigraphy with the FAD of Hindeodus parvus, which defines the base of the Triassic in Global Stratotype Section and Point (GSSP) in Meishan, China, suggests that the Hypophiceras triviale Zone is to be referred to the uppermost Permian, whereas the H. martini Zone is lowermost Triassic. Accordingly, the end-Permian marine and terrestrial extinctions and associated isotope changes as well as the subsequent adaptive radiations in East Greenland took place in latest Permian time. New Boreal faunas and floras were well established and diversified in the Hypophiceras triviale Zone prior to the beginning of the Triassic, and the Permian–Triassic boundary, in its present definition, is no longer reflecting major changes in the Earth system. It would have been fortunate if a GSSP were defined in a protracted section at a point of major environmental perturbations, marked by isotope excursions, chemical anomalies and mass extinction, rather than in the strongly condensed section like Meishan at a point which post-dates all significant events.