Mg/Ca in fossil oyster shells as palaeotemperature proxy, an example from the Palaeogene of Central Asia
Bougeois, L.; De Rafelis, M.; Reichart, G.-J.; de Nooijer, L.J.; Dupont-Nivet, G. (2016). Mg/Ca in fossil oyster shells as palaeotemperature proxy, an example from the Palaeogene of Central Asia. Palaeogeogr. Palaeoclimatol. Palaeoecol. 441(Part 4): 611–626. https://dx.doi.org/10.1016/j.palaeo.2015.09.052
In: Palaeogeography, Palaeoclimatology, Palaeoecology. Elsevier: Amsterdam; Tokyo; Oxford; New York. ISSN 0031-0182; e-ISSN 1872-616X, meer
Fossil oyster shells are well-suited to provide palaeotemperature proxies from geologic to seasonal timescalesdue to their ubiquitous occurrence from Triassic to Quaternary sediments, the seasonal nature of their shellgrowth and their relative strong resistance to post-mortemalteration. However, the common use to translate calciticoxygen isotopes into palaeotemperatures is challenged by uncertainties in accounting for past seawaterd18O, especially in shallowcoastal environmentwhere oysters calcify. In principle, theMg/Ca ratio in oyster shellscan provide an alternative palaeothermometer. Several studies provided temperature calibrations for thispotential proxy based on modern species, nevertheless their application to palaeo-studies remains hitherto unexplored.Here,we showthat past temperature variability in seawater can be obtained fromMg/Ca analyses fromselected fossil oyster species and specimens. High-resolutionMg/Ca profiles, combinedwith d18O,were obtainedalong 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/Caprofiles, defined by continuous cyclicity and reproducibilitywithin one shell, are found to be consistent for specimensof the same species but differ systematically between species, implying a dominant species-specific effecton the Mg/Ca signal. Two species studied here (Ostrea (Turkostrea) strictiplicata and Sokolowia buhsii) provide anexcellent proxy for palaeoclimate reconstruction from China to Europe in Palaeogene marine sediments. Moregenerally, the protocol developed here can be applied to identify other fossil oyster species suitable forpalaeoclimate reconstructions.
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