CONODONTS, CARBONATE, AND CLAMS: A MULTIDISCIPLINARY APPROACH TO THE LATE TRIASSIC PALEOENVIRONMENTAL RECORD OF NORTHERN VANCOUVER ISLAND, BRITISH COLUMBIA, CANADA

The Late Triassic Epoch was a time of great climatic change and faunal turnover, with the Norian – Rhaetian boundary marking the start of a prolonged interval of elevated extinction rates persisting through the Rhaetian Stage and leading into the end-Triassic mass extinction. Both the Norian – Rhaetian boundary and end-Triassic mass extinction are associated with excursions in δ¹³C values globally; however, much about the former remains enigmatic, such as the nature of the disturbance signal and possible causal mechanisms. It has been suggested that prolonged ecosystem instability spanned the Rhaetian between these two events. However, global suppression of carbonate sedimentation during the Rhaetian makes continuous stratigraphic sections amenable to carbon isotope chemostratigraphy rare. As such, this interval of time leading up to the end-Triassic mass extinction is relatively understudied, particularly in the North American (Panthalassan) region.

Late Triassic strata of the mixed carbonate-siliciclastic/volcaniclastic Parson Bay Formation is commonly exposed around the northern portion of Vancouver Island, with several localities potentially spanning both the Norian – Rhaetian and Rhaetian – Hettangian boundaries, presenting the rare opportunity to investigate these two events together. Records of δ¹³C values in carbonate are presented here for the Yreka, Holberg, and Michelsen Point stratigraphic sections, contextualized by conodont and bivalve biostratigraphic age constraints. Negative excursions in δ¹³C values of 10‰ magnitude are observed at Holberg for both the Norian – Rhaetian and Rhaetian – Hettangian boundaries. The large magnitude of these excursions suggests some degree of diagenesis or local amplification, but the coincidence with stage boundaries and the relative stability of δ¹³C_carb values outside of these excursions suggest they do reflect paleoenvironmental signals. These results lay the foundation for ongoing study of paleoenvironmental conditions leading up to the end-Triassic mass extinction in North America, and the relationship between this mass extinction and the period of high extinction rates that precede it.