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The test size and abundance variations in planktonic foraminifera Chiloguembelina cubensis and C. ototara as response to climatic events in the Oligocene

The rich and well-preserved planktonic foraminifera assemblages extracted from samples of deep sea exploration wells Istra more-3 and Istra more-4 in the northern Adriatic Sea , enabled the identification of all seven Oligocene biozones (from O1 to O7), according to a new biozonation (Wade et al., 2011). Biometric measurements were made on the tests of 20 specimens of Chiloguembelina cubensis and C. ototara recovered from the small sieve fraction (125-63 m) of each sample. Abundance was also assessed through the Oligocene. The long-lived species Chiloguembelina ototara has its lowest occurrence (LO) in Eocene Zone E9, while the species C. cubensis occurs in the uppermost Eocene (Zone E16). Chiloguembelina ototara has highest occurrence (HO) at the base of the Zone O2 and C. cubensis has HO in the North Adriatic at the end of Zone O5. Both species show fluctuations in abundance.

Adriatic Sea; climatic events; planktonic foraminifera; Oligocene; size.

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