Compound-specific carbon isotope evidence that the initial carbon isotope excursion in the end-Triassic strata in northwest Tethys is not the product of CAMP magmatism

Abstract

Compound-specific carbon isotopic analysis of biomarkers and palynological studies from sections across the end-Triassic mass extinction in the northwestern Tethys provide constraints on the origin of the bulk organic carbon ‘initial’ isotope excursion. This excursion is commonly used to correlate among geographically disparate sections that span this pivotal event associated with the rise of modern fauna. Palynological analysis is used to identify intervals of Liassic-equivalent strata in south Wales and northeast England for isotopic study. Compound-specific carbon isotope analysis of n-alkanes and regular isoprenoids from these intervals reveals a trend different than that displayed by bulk organic matter, suggesting the latter signal is not derived from large perturbations in the global carbon cycle but from localized source changes. The most pronounced changes in compound-specific isotope profiles are negative excursions in pristane and phytane, which occur within the positive phase of the bulk carbon isotope excursion and correspond to shifts in total organic carbon and increased heterotrophy. These findings indicate that a re-evaluation of temporal relationships between positive climate feedbacks and their effects is necessary to more accurately understand the likely global nature of the end-Triassic extinction, and more generally, carbon cycle perturbations associated with other mass extinction events.