Trace metal (Mg/Ca and Sr/Ca) analyses of single coccoliths by Secondary Ion Mass Spectrometry

Prentice, Katy and Jones, Tom Dunkley and Lees, Jackie and Young, Jeremy and Bown, Paul and Langer, Gerald and Fearn, Sarah and EIMF, na (2014) Trace metal (Mg/Ca and Sr/Ca) analyses of single coccoliths by Secondary Ion Mass Spectrometry. Geochimica et Cosmochimica Acta, 146. pp. 90-106. ISSN 0016-7037 DOI 10.1016/j.gca.2014.09.041

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Abstract

Here we present the first multi-species comparison of modern and fossil coccolith trace metal data obtained from single liths. We present both trace metal analyses (Sr, Ca, Mg and Al) and distribution maps of individual Paleogene fossil coccoliths obtained by Secondary Ion Mass Spectrometry (SIMS). We use this data to determine the effects of variable coccolith preservation and diagenetic calcite overgrowths on the recorded concentrations of strontium and magnesium in coccolith calcite. The analysis of coccoliths from deep-ocean sediments spanning the Eocene/Oligocene transition demonstrates that primary coccolith calcite is resistant to the neomorphism that is common in planktonic foraminifera from similar depositional environments. Instead, where present, diagenetic calcite forms distinct overgrowths over primary coccolith calcite rather than replacing this calcite. Diagenetic overgrowths on coccoliths are easily distinguished in SIMS analyses on the basis of relatively higher Mg and lower Sr concentrations than co-occurring primary coccolith calcite. This interpretation is confirmed by the comparable SIMS analyses of modern cultured coccoliths of Coccolithus braarudii. Further, with diagenetic calcite overgrowth being the principle source of bias in coccolith-based geochemical records, we infer that lithologies with lower carbonate content, deposited below the palaeo-lysocline, are more likely to produce geochemical records dominated by primary coccolith calcite than carbonate-rich sediments where overgrowth is ubiquitous. The preservation of primary coccolith carbonate in low-carbonate lithologies thus provides a reliable geochemical archive where planktonic foraminifera are absent or have undergone neomorphism.

Item Type: Article
Uncontrolled Keywords: 2014AREP; IA68;
Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Divisions: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Journal or Publication Title: Geochimica et Cosmochimica Acta
Volume: 146
Page Range: pp. 90-106
Identification Number: 10.1016/j.gca.2014.09.041
Depositing User: Sarah Humbert
Date Deposited: 24 Nov 2014 18:08
Last Modified: 18 Dec 2014 17:39
URI: http://eprints.esc.cam.ac.uk/id/eprint/3168

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