Title: Additive effects of acidification and mineralogy on calcium isotopes in Triassic/Jurassic boundary limestones

Abstract

The end-Triassic mass extinction coincided with a negative δ¹³ C excursion, consistent with release of ¹³C-depleted CO₂ from the Central Atlantic Magmatic Province. However, the amount of carbon released and its effects on ocean chemistry are poorly constrained. The co upled nature of the carbon and calcium cycles allows calcium isotopes to be used for constraining carbon cycle dynamics and vice versa. We present a high-resolution calcium isotope (δ^44/40 Ca) record from 100 m of marine limestone spanning the Triassic/Jurassic boundary in two stratigraphic sections from northern Italy. Immediately above the extinction horizon and the associated negative excursion in δ¹³ C, δ^44/40 Ca decreases by ca. 0.8‰ in 20 m of section and then recovers to preexcursion values. Coupled numerical models of the geological carbon and calcium cycles demonstrate that this δ^44/40 Ca excursion is too large to be explained by changes to seawater δ^44/40 Ca alone, regardless of CO₂ injection volume and duration. Less than 20% of the δ 44/40 Ca excursion can be attributed to acidification. The remaining 80% likely reflects a higher proportion of aragonite in the original sediment, based largely on high concentrations of Sr in the samples. Our study demonstrates that coupled models of themore » carbon and calcium cycles have the potential to help distinguish contributions of primary seawater isotopic changes from local or diagenetic effects on the δ^44/40 Ca of carbonate sediments. Finally, differentiating between these effects is critical for constraining the impact of ocean acidification during the end-Triassic mass extinction, as well as for interpreting other environmental events in the geologic past.« less

Authors:

Jost, Adam B.  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-3934-704X"

Bachan, Aviv ^[1]; van de Schootbrugge, Bas  ^[2];

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• Search DOE PAGES for ORCID "0000-0003-2270-6285"

Brown, Shaun T.  ^[3];

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• Search DOE PAGES for ORCID "0000-0002-2159-6718"

DePaolo, Donald J. ^[3]; Payne, Jonathan L.  ^[1]

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• Search DOE PAGES for ORCID "0000-0002-9601-3310"

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1. Stanford Univ., CA (United States). Dept. of Geological Sciences
2. Utrecht Univ., Utrecht (Netherlands). Dept. of Earth Sciences
3. Univ. of California, Berkeley, CA (United States). Dept. of Earth and Planetary Sciences; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Earth Science Division, Geochemistry Dept.

Publication Date:

Thu Dec 29 00:00:00 EST 2016

Research Org.:

Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1398458

Grant/Contract Number:  

AC02-05CH11231

Resource Type:

Accepted Manuscript

Journal Name:

Geochemistry, Geophysics, Geosystems

Additional Journal Information:

Journal Volume: 18; Journal Issue: 1; Journal ID: ISSN 1525-2027

Publisher:

American Geophysical Union

Country of Publication:

United States

Language:

English

Subject:

58 GEOSCIENCES; calcium isotopes; Triassic; Jurassic; carbon isotopes; extinction; aragonite