Abstract

Microstructure, mineralogy and elemental and isotopic compositions of recent and fossil otoliths have been investigated. Fossil otoliths come from marine Pliocene localities of southeastern France. The study of the different parameters show that diagenetic changes are weak. Microstructural features specific to otoliths, such as needle-like crystals and growth increments, are usually well preserved. When present, the microstructural modifications remain limited inside each otolith. Except a few pyritic specimens, the only mineral found is aragonite like in recent specimens. The chemical compositions of fossil and recent otoliths are not significantly different, and any element is preferentially changed by diagenesis. The isotopic composition does not show strong alterations. However, the difference in 18 O content between recent fishes having different ecological habits is not found with the same magnitude in fossil specimens. Finally, when elemental and isotopic compositions are compared, the specimens are sorted according to taxonomy and not according to their geologic age. This suggests that biogenic signals have been preserved.

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