Stable oxygen and carbon isotope profiles of the Early Pliocene fossil Akebiconcha kawamurai from the Tamari Formation, Central Japan, are constructed to obtain environmental and physiological information using a series of samples from the shell surface for a high-resolution record. The δ
18O profile indicates that hydrographic conditions were stable and similar to those of modern bathyal depths. The isotopic temperature was estimated to be around 6 to 8°C with a little seasonal variation. The δ
13C profile shows an apparently progressive by increasing trend during shell growth, a feature which has been identified from some live mollusks containing symbiotic bacteria. Therefore, the stable isotopic geochemical profiles are regarded as potential indicators of the paleoecological habitat and symbiosis with chemoautotrophic bacteria of fossil mollusks.
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