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Calcium isotope evidence for environmental variability before and across the Cretaceous-Paleogene mass extinction

Benjamin J. Linzmeier, Andrew D. Jacobson, Bradley B. Sageman, Matthew T. Hurtgen, Meagan E. Ankney, Sierra V. Petersen, Thomas S. Tobin, Gabriella D. Kitch and Jiuyuan Wang
Calcium isotope evidence for environmental variability before and across the Cretaceous-Paleogene mass extinction
Geology (Boulder) (October 2019) 48 (1): 34-38


Carbon dioxide release during Deccan Traps volcanism and the Chicxulub impact likely contributed to the Cretaceous-Paleogene (K-Pg) mass extinction; however, the intensity and duration of CO (sub 2) input differed between the two events. Large and rapid addition of CO (sub 2) to seawater causes transient decreases in pH, [CO (sub 3) (super 2-) ], and carbonate mineral saturation states. Compensating mechanisms, such as dissolution of seafloor sediment, reduced biomineralization, and silicate weathering, mitigate these effects by increasing the same parameters. The calcium isotope ratios (delta (super 44/40) Ca) of seawater and marine carbonates are hypothesized to respond to these perturbations through weathering/carbonate deposition flux imbalances and/or changes in fractionation between carbonate minerals and seawater. We used a high-precision thermal ionization mass spectrometry method to measure delta (super 44/40) Ca values of aragonitic bivalve and gastropod mollusk shells from the K-Pg interval of the Lopez de Bertodano Formation on Seymour Island, Antarctica. Well-preserved shells spanning the late Maastrichtian (ca. 67 Ma) to early Danian (ca. 65.5 Ma) have delta (super 44/40) Ca values ranging from -1.89 ppm to -1.57 ppm (seawater [sw]). Shifts in delta (super 44/40) Ca inversely correlate with sedimentological indicators of saturation state. A negative excursion begins before and continues across the K-Pg boundary. According to a simple mass-balance model, neither input/output flux imbalances nor change in the globally integrated bulk carbonate fractionation factor can produce variations in seawater delta (super 44/40) Ca sufficient to explain the measured trends. The data are consistent with a dynamic molluscan Ca isotope fractionation factor sensitive to the carbonate geochemistry of seawater. The K-Pg extinction appears to have occurred during a period of carbonate saturation state variability caused by Deccan volcanism.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 48
Serial Issue: 1
Title: Calcium isotope evidence for environmental variability before and across the Cretaceous-Paleogene mass extinction
Affiliation: Northwestern University, Department of Earth and Planetary Sciences, Evanston, IL, United States
Pages: 34-38
Published: 20191028
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 52
Accession Number: 2019-095301
Categories: StratigraphyIsotope geochemistry
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sketch map
S64°19'60" - S64°12'00", W56°53'60" - W56°34'60"
Secondary Affiliation: University of Michigan, USA, United StatesUniversity of Alabama, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201950
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