Crenostrea sp. cf. C. cannoni (Marwick 1928) (Bivalvia: Ostreoidea) and associated fauna from east of Heard Island, Kerguelen Plateau: age and palaeoenvironmental value

A well-preserved single left valve of a large oyster embedded in coarse volcaniclastic sediment and identified as Crenostrea sp. cf. C. cannoni (Marwick, 1928) was dredged from east of Heard Island, central southern Indian Ocean. It is accompanied by a fragment of the pectinid bivalve Austrochlamys sp. indet. and foraminifera. Austrochlamys sp. indet. and other bivalve fragments were analysed for ⁸⁷Sr/⁸⁶Sr, δ¹⁸O and δ¹³C, the results yielding an age of 17.5 Ma (later early Miocene) and a water temperature of ca 10°C. Foraminifera and sediment characteristics indicate that accumulation occurred in mid-continental shelf depths, at a location where nutrient supply was good.