We found a match
Your institution may have access to this item. Find your institution then sign in to continue.
- Title
The Calcium Isotope (δ<sup>44/40</sup>Ca) Record Through Environmental Changes: Insights From the Late Triassic.
- Authors
Kovács, Zsófia; Demangel, Isaline; Baldermann, Andre; Hippler, Dorothee; Schmitt, Anne‐Désirée; Gangloff, Sophie; Krystyn, Leopold; Richoz, Sylvain
- Abstract
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. Plain Language Summary: During Earth's history, profound environmental changes happened, which are recorded in geological samples and accessible through proxy methods. We measured Late Triassic carbonates for their Ca isotopic composition. The Late Triassic witnessed important environmental and ecological turnovers, such as the first appearance of calcareous nannoplankton, mass extinction and ocean acidification associated with CO2 emission from a large volcanic province. These multiple events help to understand, which factors influenced the Ca‐isotope record of seawater recorded in marine carbonates. This in turn helps to clarify, which events affected significantly the ocean chemistry. Our results reveal, although Ca isotopes are suitable to recognize global environmental changes, local factors also influence the isotopic pattern of single records. We could confirm that both volcanic events and the emergence of planktonic calcifiers have small effects on this isotope system at this time. An increase in the ratio of Ca input to the ocean over the amount of Ca removed through carbonate sedimentation, appears to have played the biggest role in driving the seawater isotope record at this. The observed changes in Ca isotopic ratios can be best explained by a sea‐level drop together with a change in the dominant rock types weathered on the continent. Key Points: A δ44/40Ca decrease in the Late Triassic is consistent with a change in Ca flux to the ocean due to a major sea‐level fallLarge volcanism during the end‐Triassic mass extinction (201.6 Ma) is associated with a small negative δ44/40Ca excursionContemporaneous records of different paleoenvironments show a δ44/40Ca offset due to local differences in mineralogy and early diagenesis
- Subjects
CALCIUM isotopes; GLOBAL environmental change; CHEMICAL weathering; CARBONATE minerals; CARBONATE rocks; OCEAN acidification; CALCIUM; VOLCANISM
- Publication
Geochemistry, Geophysics, Geosystems: G3, 2022, Vol 23, Issue 12, p1
- ISSN
1525-2027
- Publication type
Article
- DOI
10.1029/2022GC010405