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Mg/Ca in fossil oyster shells as palaeotemperature proxy, an example from the Palaeogene of Central Asia

Abstract : Fossil oyster shells are well-suited to provide palaeotemperature proxies from geologic to seasonal timescales due to their ubiquitous occurrence from Triassic to Quaternary sediments, the seasonal nature of their shell growth and their strong resistance to post-mortem alteration. However, the common use to translate calcitic oxygen isotopes into palaeotemperatures is challenged by uncertainties in accounting for past seawater δ 18 O, especially in shallow coastal environment where oysters calcify. In principle, the Mg/Ca ratio in oyster shells can provide an alternative palaeothermometer. Several studies provided temperature calibrations for this potential proxy based on modern species, nevertheless their application to palaeo-studies remains hitherto unexplored. Here, we show that past temperature variability in seawater can be obtained from Mg/Ca analyses from selected oyster fossil species and specimens. High-resolution Mg/Ca profiles, combined with δ 18 O, were obtained along 41 fossil oyster shells of seven different species from the Palaeogene Proto-Paratethys sea (Central Asia) found in similar as well as different depositional age and environments providing comparison. Suitable Mg/Ca profiles, defined by continuous cyclicity and reproducibility within one shell, are found to be consistent for specimens of the same species but differ systematically between species, implying a dominant species-specific effect on the Mg/Ca incorporation. Two species studied here (Ostrea (Turkostrea) strictiplicata and Sokolowia buhsii) provide an excellent proxy ACCEPTED MANUSCRIPT for palaeoclimate reconstruction from China to Europe in Palaeogene marine sediments. More generally , the protocol developed here can be applied to identify other fossil oyster species suitable for palaeoclimate reconstructions.
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Submitted on : Friday, October 16, 2015 - 11:03:24 AM
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Laurie Bougeois, Marc de Rafélis, Gert-Jan Reichart, Lennart de Nooijer, Guillaume Dupont-Nivet. Mg/Ca in fossil oyster shells as palaeotemperature proxy, an example from the Palaeogene of Central Asia. Palaeogeography, Palaeoclimatology, Palaeoecology, Elsevier, 2016, 441 (4), pp.611-626. ⟨10.1016/j.palaeo.2015.09.052⟩. ⟨insu-01216384⟩

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