The Calcium Isotope (δ44/40Ca) Record Through Environmental Changes : Insights From the Late Triassic

Calcium isotopes (δ44/40Ca) are particularly useful in palaeo-environmental studies due to the key role of carbonate minerals in continental weathering and their formation in seawater. The calcium isotope ratio can provide hints on past changes in the calcium fluxes, environmental shifts, ecological...

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Bibliographic Details
Published in:Geochemistry, Geophysics, Geosystems
Main Authors: Kovács, Zsófia, Demangel, Isaline, Baldermann, Andre, Hippler, Dorothee, Schmitt, Anne Désirée, Gangloff, Sophie, Krystyn, Leopold, Richoz, Sylvain
Format: Article in Journal/Newspaper
Language:English
Published: American Geophysical Union (AGU) 2022
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Online Access:https://lup.lub.lu.se/record/179769f7-6da5-4795-b403-10c422258072
https://doi.org/10.1029/2022GC010405
Description
Summary:Calcium isotopes (δ44/40Ca) are particularly useful in palaeo-environmental studies due to the key role of carbonate minerals in continental weathering and their formation in seawater. The calcium isotope ratio can provide hints on past changes in the calcium fluxes, environmental shifts, ecological factors and alternatively diagenesis of carbonate rocks. The investigation of the Late Triassic calcium isotope record offers a great opportunity to evaluate such factors in a time interval that witnessed important environmental and ecological turnovers, such as the first appearance of calcareous nannoplankton, ocean acidification and periods of elevated extinction rates. In this study, we present a δ44/40Ca data set from the upper Norian (Upper Triassic) through the lower Hettangian (Lower Jurassic) interval. The isotope records reveal two globally significant signals: a ∼ 0.20‰ decrease through the early Rhaetian (Upper Triassic) and a small, negative (∼0.14‰) excursion corresponding to the emplacement of the Central Atlantic Magmatic Province, at the end of the Triassic. The possible explanations for these signals are changes in the isotopic ratio of the continental calcium influx to the ocean due to the high chemical weathering rate of carbonates and possibly ocean acidification, respectively. The considerable (∼0.15–0.30‰) offset in δ44/40Ca between study areas is likely the combined result of local differences in lithology and early marine diagenesis. The major evolutionary step represented by the first occurrence of calcareous nannoplankton did not have at this time a determining role on the calcium isotopic signature of the marine carbonates.