DEVELOPING A FACIES MODEL FOR AN EARLY TRIASSIC SEAMOUNT IN THE PANTHALASSIC OCEAN

The late Smithian thermal maximum marks the hottest interval of the Early Triassic, following the end-Permian mass extinction, an event responsible for the greatest loss in biodiversity of the Phanerozoic. Most interpretations of the end-Permian extinction event are derived from Tethyan carbonate shelf and platform settings. The Panthalassic Ocean is not as well documented, due to subduction-related processes resulting in poor preservation of oceanic sediments, which are now limited to accretionary complexes. The Jesmond section is part of the Cache Creek Terrane, a Panthalassic accretionary complex in central British Columbia, Canada. The section represents a Spathian-age atoll-like structure that developed in response to the subsidence of an underlying seamount, as well as minor sea-level fluctuations. Geochemical and petrographic analysis of Jesmond samples provides the basis for developing a facies model for the section and understanding more about how life recovered from late Smithian thermal stress. Thin section observations and geochemical evidence suggest that the Jesmond section is well preserved, despite early, fabric-retentive dolomitization. Early diagenetic spar infills are intersected bedding-parallel stylolites, indicating dolomitization prior to burial compaction. This dolomitization history is consistent with the interpreted depositional environment, being non-stoichiometric. The eight microfacies identified within the Jesmond section are as follows: Fenestral Mudflat, Laminated Bindstone, Silicified Wackestone, Calcitic Mudstone, Bioclastic Wacke-Packestone, Wavy-bedded Bindstone, Domal Laminated, and a Lagoonal Facies. Despite low biodiversity, with microbialites being the primary reef building organism, this carbonate factory was productive enough to maintain its position in the photic zone despite sea level rise and subsidence of the underlying seamount.