An extended organic carbon-isotope record across the Triassic–Jurassic boundary in the Queen Charlotte Islands, British Columbia, Canada

Abstract

New lithologic and organic carbon-isotope data are presented for the Triassic–Jurassic boundary section at Kennecott Point, Queen Charlotte Islands, British Columbia, Canada. The previously reported Late Norian to earliest Hettangian record is extended by over 130 m, and three new isotopic features are revealed. The record now shows a negative offset in baseline carbon isotope values from approximately -29‰ in the Late Norian to -31‰ in the Hettangian. This offset is accompanied by the previously reported 2‰ negative excursion at the Triassic–Jurassic boundary and a 5‰ positive excursion in the early Hettangian. There is a significant long-term negative isotopic trend in the Hettangian interval of the section, which may be due to CAMP volcanism. The positive excursion is attributed to a decline in bio-calcification as well as changes in microbial ecology, both related to the mass extinction at the Triassic–Jurassic boundary.