Carbon and nitrogen isotope disturbances and an end-Norian (Late Triassic) extinction event

Sephton, Mark A.; Amor, Ken; Franchi, Ian A.; Wignall, Paul B.; Newton, Robert and Zonneveld, John-Paul (2002). Carbon and nitrogen isotope disturbances and an end-Norian (Late Triassic) extinction event. Geology, 30(12) pp. 1119–1122.

DOI: https://doi.org/10.1130/0091-7613(2002)030%3C1119:CANIDA%3E2.0.CO;2

Abstract

Major perturbations of organic carbon and nitrogen isotope ratios from a Norian-Rhaetian (Late Triassic) boundary section in British Columbia coincide with an extinction of the dominant, deep-water invertebrate fauna of the Late Triassic (monotids and most ammonoids). The carbon isotope excursion is attributed to the development of widespread oceanic stagnation that favored organic-rich shale deposition. The coincident nitrogen isotope excursion suggests that progressively more nitrate-limited productivity forced a change to nitrogen-fixing cyanobacteria populations as ocean stagnation created nutrient-starved conditions. The biotic crisis and geochemical events of the Norian-Rhaetian boundary predate the latest Rhaetian (end-Triassic) mass extinction. Thus, the Late Triassic interval was marked by more than one extinction event.

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