Serravallian-Tortonian hydrological isolation of the Eastern Paratethys from the perspective of the Caspian Basin: Sarmatian s.l. integrated stratigraphy and biotic record of Karagiye, Kazakhstan.

The Eastern Paratethys (EP) is a former epicontinental basin that unified the Black Sea, Caspian Sea and the Dacian Basin and played a crucial role in shaping of the west Eurasian paleoecosystems.

In the late Middle-Late Miocene, during Sarmatian sensu lato Stage, the EP underwent a gradual hydrological isolation from the global ocean. This process was accompanied by adaptation and radiation of endemic faunas in the early and middle Sarmatian s.l. (Volhynian and Bessarabian) and by the near complete extinction of marine life forms in the late Sarmatian s.l. (Khersonian). The drivers of this ecological crisis still remain ununderstood. We present our integrated stratigraphic study of 130-m-thick outcrop Karagiye, Caspian Basin. The preliminary data demonstrate:

1. Incomplete Volhynian record (12.3–12.05 Ma). Proximal lagoon with molluscs Obsoletiformes and Ervilia, ostracod zones Cytheridea hungarica and Euxinocythere turpe, foraminfera zones Veridentella reussi and Elphidium reginum, rich marine vertebrate fauna;
2. Bessarabian offshore to lagoon record (11.9–9.8 Ma) with molluscs Plicatiformes plicatofittoni, Sarmatimactra vitaliana, ostracod zones Euxinocuthere grave odessoensis and Loxoconcha subcrassula, foraminifera zones Dogielina sarmatica and Porosononion aragviensis, rich marine vertebrate fauna.
3. Khersonian shallow water barrier island to foreshore (9.4–7.6 Ma) with molluscs Chersonimactra caspia and Ch. bulgarica, ostracod zones – Euxinocythere immutata and E.dilecta, foraminifera and marine vertebrate fauna missing.

Our ongoing study for the first time provides well-dated mollusc and microfauna zonations of the Sarmatian s.l. substages in the Caspian Basin.