1024 An early Middle Miocene warm-water molluscan fauna in southwestern Sakhalin : Molluscs from the Ausinskaya Formation around Novoselovo

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Thirty-two mollusc species were identified from two localities of the lower Middle Miocene Ausinskaya Formation around Novoselovo, southwestern Sakhalin. This fauna includes a number of warm-water taxa such as Anadara watanabei, Glycymeris cisshuensis, Dosinia tugaruana, Tateiwaia sp., Euspira meisensis, and Cultellus izumoensis. These taxa were previously unknown in the Ausinskaya Formation, except for Cultellus izumoensis. A Dosinia-Anadara association made up of subtropical to temperate-water euneritic dwellers is prominent in this fauna, as is a temperate- to cold-water, eu- to mesoneritic Spisula association that has been recognized in lower Middle Miocene strata of northwestern Hokkaido and northwestern Sakhalin. The cooccurrence of these two ecologically dissimilar faunal associations implies that adjacent warm (inshore) and cold (offshore) water masses were present within the temperate marine realm that prevailed in Hokkaido and in southwestern Sakhalin during the early Middle Miocene.