Significant increases in global weathering during Oceanic Anoxic Events 1a and 2 indicated by calcium isotopes

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doi: 10.1016/j.epsl.2011.06.029
Author(s): Blättler, Clara L.; Jenkyns, Hugh C.; Reynard, Linda M.; Henderson, Gideon M.
Author Affiliation(s): Primary:
University of Oxford, Department of Earth Sciences, Oxford, United Kingdom
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, 309(1-2), p.77-88. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. Supplementary data available in online version. 89 refs.; illus.
Summary: Calcium-isotope ratios (δ44/42Ca) were measured in carbonate-rich sedimentary sections deposited during Oceanic Anoxic Events 1a (Early Aptian) and 2 (Cenomanian-Turonian). In sections from Resolution Guyot, Mid-Pacific Mountains; Coppitella, Italy; and the English Chalk at Eastbourne and South Ferriby, UK, a negative excursion in δ44/42Ca of ∼0.20 ppm and ∼0.10 ppm is observed for the two events. These δ44/42Ca excursions occur at the same stratigraphic level as the carbon-isotope excursions that define the events, but do not correlate with evidence for carbonate dissolution or lithological changes. Diagenetic and temperature effects on the calcium-isotope ratios can be discounted, leaving changes in global seawater composition as the most probable explanation for δ44/42Ca changes in four different carbonate sections. An oceanic box model with coupled strontium- and calcium-isotope systems indicates that a global weathering increase is likely to be the dominant driver of transient excursions in calcium-isotope ratios. The model suggests that contributions from hydrothermal activity and carbonate dissolution are too small and short-lived to affect the oceanic calcium reservoir measurably. A modelled increase in weathering flux, on the order of three times the modern flux, combined with increased hydrothermal activity due to formation of the Ontong-Java Plateau (OAE1a) and Caribbean Plateau (OAE2), can produce trends in both calcium and strontium isotopes that match the signals recorded in the carbonate sections. This study presents the first major-element record of a weathering response to Oceanic Anoxic Events.
Year of Publication: 2011
Research Program: ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Alkaline earth metals; Ca-44/Ca-42; Calcium; Carbonates; Cenomanian; Chalk Aquifer; Coppitella Italy; Cretaceous; Eastbourne England; England; Europe; Global; Great Britain; Isotope ratios; Isotopes; Italy; Leg 143; Lincolnshire England; Marine sediments; Mesozoic; Metals; Mid-Pacific Mountains; North Pacific; ODP Site 866; Ocean Drilling Program; Oceanic anoxic events; Ontong Java Plateau; Pacific Ocean; Paleoenvironment; Radioactive isotopes; Resolution Seamount; Sediments; South Ferriby Quarry; Southern Europe; Stable isotopes; Turonian; United Kingdom; Upper Cretaceous; Weathering; Weathering rates; West Pacific; Western Europe
Coordinates: N534200 N534200 W0003000 W0003000
N504200 N504200 E0001800 E0001800
N415400 N415400 E0161200 E0161200
N211957 N211958 E1741853 E1741850
Record ID: 2011102554
Copyright Information: GeoRef, Copyright 2018 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands