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Early diagenetic overprint in Caribbean sediment cores and its effect on the geochemical composition of planktonic foraminifera
1Leibniz Institute of Marine Sciences IFM-GEOMAR, Kiel, Germany
2Faculty of Earth Sciences, Utrecht University, The Netherlands
Abstract. Early diagenetic features are noticed in the vicinity of carbonate platforms. Planktonic foraminifera of two tropical Atlantic deep-sea sediment cores show the strict relation between micro-scale euhydral crystallites of inorganic precipitates, higher oxygen isotope values and Mg/Ca ratios, and lower Sr/Ca ratios than expected for their pelagic environment in the time interval of ~100 000–550 000 calendar years before present. Laser ablation Mg/Ca (Sr/Ca) of crystallite-bearing foraminiferal chamber walls revealed 4–6 times elevated (2–3 times depleted) ratios, when ablating the diagenetic overgrowth. Crystalline overgrowth in proportions of 10–20% are estimated to cause the observed geochemical alteration. The extent of foraminiferal Mg/Ca alteration, moreover, seems to be controlled by the composition of the bulk sediment, especially the content of high-magnesium calcite. Anomalous ratios of >6 mmol/mol only occur, when high-magnesium calcite has dissolved within the sediment. The older parts (back to ~800 kyrs) of the records are characterized by similar trends of Mg/Ca and Sr/Ca. We discuss possible scenarios to accommodate the obtained geochemical information.
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Citation: Regenberg, M., Nürnberg, D., Schönfeld, J., and Reichart, G.-J.: Early diagenetic overprint in Caribbean sediment cores and its effect on the geochemical composition of planktonic foraminifera, Biogeosciences Discuss., 4, 2179-2213, 2007. Bibtex EndNote Reference Manager
