Molecular and isotopic evidence reveals the end-Triassic carbon isotope excursion is not from massive exogenous light carbon

The negative organic carbon isotope excursion (CIE) associated with the end-Triassic mass extinction (ETE) is conventionally interpreted as the result of a massive flux of isotopically light carbon from exogenous sources into the atmosphere (e.g., thermogenic methane and/or methane clathrate dissoci...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences
Main Authors: Fox, Calum P., Cui, X., Whiteside, J.H., Olsen, P.E., Summons, R.E., Grice, Kliti
Format: Article in Journal/Newspaper
Language:English
Published: NATL ACAD SCIENCES 2020
Subjects:
Science & Technology
Multidisciplinary Sciences
Science & Technology - Other Topics
large igneous provinces
carbon isotopes
end-Triassic mass extinction
biomarkers
PHOTIC ZONE EUXINIA
SEA-LEVEL CHANGE
JURASSIC BOUNDARY HORIZONS
ATLANTIC MAGMATIC PROVINCE
FRESH-WATER MICROBIALITES
LOWER RHINE BASIN
PALEOENVIRONMENTAL CONDITIONS
2-METHYLHOPANOID PRODUCTION
FACIES DEVELOPMENT
CUATRO CIENEGAS
Ocean acidification
Online Access:https://hdl.handle.net/20.500.11937/90127
https://doi.org/10.1073/pnas.1917661117
Description
Summary:The negative organic carbon isotope excursion (CIE) associated with the end-Triassic mass extinction (ETE) is conventionally interpreted as the result of a massive flux of isotopically light carbon from exogenous sources into the atmosphere (e.g., thermogenic methane and/or methane clathrate dissociation linked to the Central Atlantic Magmatic Province [CAMP]). Instead, we demonstrate that at its type locality in the Bristol Channel Basin (UK), the CIE was caused by a marine to nonmarine transition resulting from an abrupt relative sea level drop. Our biomarker and compound-specific carbon isotopic data show that the emergence of microbial mats, influenced by an influx of fresh to brackish water, provided isotopically light carbon to both organic and inorganic carbon pools in centimeter-scale water depths, leading to the negative CIE. Thus, the iconic CIE and the disappearance of marine biota at the type locality are the result of local environmental change and do not mark either the global extinction event or input of exogenous light carbon into the atmosphere. Instead, the main extinction phase occurs slightly later in marine strata, where it is coeval with terrestrial extinctions and ocean acidification driven by CAMP-induced increases in PCO2; these effects should not be conflated with the CIE. An abrupt sea-level fall observed in the Central European basins reflects the tectonic consequences of the initial CAMP emplacement, with broad implications for all extinction events related to large igneous provinces.

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