Mathematics – Logic
Scientific paper
Sep 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011e%26psl.309...77b&link_type=abstract
Earth and Planetary Science Letters, Volume 309, Issue 1-2, p. 77-88.
Mathematics
Logic
Calcium Isotopes, Oae, Weathering, Cretaceous
Scientific paper
Calcium-isotope ratios (δ 44/42 Ca) 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 δ 44/42 Ca of ~ 0.20‰ and ~ 0.10‰ is observed for the two events. These δ 44/42 Ca 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 δ 44/42 Ca 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.
Blättler Clara L.
Henderson Gideon M.
Jenkyns Hugh C.
Reynard Linda M.
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