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Oligocene planktonic foraminifera from Adriatic Sea

This detailed biostratigraphical study is based on material from drill cuttings and two core intervals (1185, 5-1195, 5 m and 968, 0-974, 0 m) from deep exploration Well Istra More-3. The well is located in the North part of the Adriatic Sea on the edge of Adriatic Carbonate Platform towards the Venetian Basin. In general, Oligocene sediments consists of monotonous silty marls with rare and thin siltstone beds. The base of the Oligocene tops upper Eocene sediments. The Oligocene sediments are overlain by lower Miocene deposits. Selected samples from cuttings and cored intervals were washed through 63μ m, 125μ m, 160μ m, 250μ m and 315μ m mesh sieves. In the studied material several index species of planctonic foraminifera enabled application of biozonation following BERGGREN et al. (1995) and BERGGREN & PEARSON (2005). Based on planktonic foraminifera six Oligocene biostratigraphic Zones were determined (Zones O1 to O6). Biozones were defined based on the highest occurance (HO) of the specific index species. Exception was the boundary between O3 (P20) and O4 (P21a) Zones which was defined by lowest occurrence (LO) of Globigerina angulisuturalis (BERGGREN et al., 1995 ; BERGGREN & PEARSON , 2005). When the placement of LO of the index fossil was too difficult in the studied material, zonal boundaries were identified based on the entire planktonic foraminiferal assemblage. The boundary between the lower and upper Oligocene (zones O4 and O5) was placed on the basis of the HCO of the species Chiloguembelina cubensis. Both cored intervals (1185, 5-1195, 5 m and 968, 0-974, 0 m) were investigated. Planktonic foraminiferal association from the first cored interval (Zone O2) contains the following species: Turborotalia ampliapertura, T. increbecens, Dentoglobigerina galavisi, Dentoglobigerina sp., Tenuitella gemma, T. munda, Globigerina sp., Chiloguembelina cubensis, Subbotina corpulenta, Catapsydrax unicavus, Paragloborotalia sp., Globigerina sp., Globorotaloides sp. In the second cored interval 968, 0-974, 0 m (Zone O5) very well preserved and diversified planktonic foraminiferal assemblages are identified. The following planktonic foraminiferal species and genera are: Globoturborotalita angulisuturalis, G. ciperoensis, G. anguliofficinalis, G. occlusa, Globoturborotalita sp., Paragloborotalia sp., P. nana, Turborotalita sp., Dentoglobigerina sp., Globigerinella obesa, Chiloguembelina cubensis, Catapsydrax sp., Globigerina sp., Tenuitella sp. The very well preserved planktonic foraminiferal associations from the Well More-3 well, need further study (e.g., biodiversity indices, morphometry of species, and stable isotopes).

biostratigraphy; planktonic foraminifera; Oligocene; Adriatic Sea; exploration well

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