Revisiting diagenesis on the Ontong Java Plateau: Evidence for authigenic crust precipitation in Globorotalia tumida

Branson, Oscar and Read, Elizabeth and Redfern, Simon A. T. and Rau, Christoph and Elderfield, Henry (2015) Revisiting diagenesis on the Ontong Java Plateau: Evidence for authigenic crust precipitation in Globorotalia tumida. Paleoceanography. ISSN 0883-8305 DOI

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The calcite tests of foraminifera lie in marine sediments for thousands to millions of years, before being analyzed to generate trace element and isotope paleoproxy records. These sediments constitute a distinct physio-chemical environment from the conditions in which the tests formed. Storage in sediments can modify the trace element and isotopic content of foraminiferal calcite through diagenetic alteration, which has the potential to confound their paleoceanographic interpretation. A previous study of Globorotalia tumida from the Ontong Java Plateau, western equatorial Pacific, found that preferential dissolution of higher-Mg chamber calcite and the preservation of a low-Mg crust on the tests significantly reduced whole-test Mg/Ca and Sr/Ca. Here we revisit specimens with a combination of synchrotron X-ray computed tomography (sXCT) and electron probe microanalyses to reevaluate the nature of their diagenetic alteration. The dissolution of higher-Mg calcite with depth was directly observed in the sXCT data, confirming the inference of the previous study. The sXCT data further reveal a thickening of the chemically and structurally distinct calcite crust with depth. We propose that these crusts have a diagenetic origin, driven by the simultaneous dissolution of high-Mg chamber calcite and precipitation of low-Mg crust from the resulting modified pore water solution. While the breadth of the study is limited by the nature of the techniques, the observation of both dissolution and reprecipitation of foraminiferal calcite serves to demonstrate the action of two simultaneous diagenetic alteration processes, with significant impacts on the resulting paleoproxy signals.

Item Type: Article
Additional Information: Accepted manuscript online: 16 October 2015 Manuscript Accepted: 2 October 2015
Uncontrolled Keywords: 2015AREP; IA69; weekly list
Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Divisions: 01 - Climate Change and Earth-Ocean Atmosphere Systems
08 - Green Open Access
Journal or Publication Title: Paleoceanography
Identification Number:
Depositing User: Sarah Humbert
Date Deposited: 19 Nov 2015 18:12
Last Modified: 17 May 2016 00:00

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