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 <i>Crenostrea</i> sp. cf. <i>C. cannoni</i> (Marwick, 1928) was dredged from east of Heard Island, central southern Indian Ocean. It is accompanied by a fragment of the pectinid bivalve <i>Austrochlamys</i> sp. indet. and foraminifera. <i>Austrochlamys</i> 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 <i>ca</i> 10°C. Foraminifera and sediment characteristics indicate that accumulation occurred in mid-continental shelf depths, at a location where nutrient supply was good.