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Sarmatian calcareous nannofossil zonation of Mt. Medvednica (NW Croatia, Paratethys)

Representative Sarmatian geological sections had been investigated at southwestern to south and north to northeastern part of Mt. Medvednica. This SW part of Paratethys belongs to the perifer "Sarmatian Sea". Layers consists mostly of marly sediments (tripolite). Biozone succession of deposits ranges from the upper part of the NN6 to the NN8 Zone of calcareous nannofossils (Martini, 1971). The beginning of the Sarmatian defined the upper part of the NN6 - lower part of the NN7 Zone (Perch-Nielsen, 1985), which was indentified on NE slope of Mt. Medvednica. It is characterised in monofloral development of nannoplankton: Reticulofenestra pseudoumbilica and Perforocalcinella fusiformis. The species P. fusiformis is characteristic for the Sarmatian (Bajraktarević, 1984). The warmer marine environment (R. pseudoumbilica) was under direct influence of river input, what caused a drop of salinity (P. fusiformis). The boundary of the NN6/NN7 Zone was defined on NE part of Mt. Medvednica. It is marked by last occurrence or absence of Cyclicargolithus floridanus, which is replaced by abundant R. peseudoumbilica. The Discoaster kugleri - NN7 Zone was identified for the first time in N, SW and S part of Mt. Medvednica (Bajraktarević, 1984). The nannoplankton assemblages of this Zone are characterised by: Calcidiscus leptoporus, C. macintyrei, Coccolithus miopelagicus, Co. pelagicus, Cyclococcolithus rotula, Discoaster exilis, D. kugleri, D. variabilis, Perforocalcinella fusiformis, Reticulofenestra pseudoumbilica and Umbilicosphaera jafari. The laminated marly sediments of the varve type (tripolite) was deposited in a semi-enclosed basin (coccospheres). Near-shore area of the marginal marine zone, where the upwelling occurs (Co. pelagicus, Helicosphaera carteri), was under influence of seasonal changes in more temperate climate. The increased eutrophication, caused nannoplankton blooms (Puškarić et al., 1990). In warmer periods when the thermo- and halocline have formed, Perforocalcinella fusiformis flourish the surface layers as a result of brachish/marine conditions. The boundary of the NN7/NN8 Zone has been established on the SW, S , SE and N part of Mt. Medvednica. The disappearance of Co. miopelagicus (Perch-Nielsen, 1985 ; Iaccarino et al., 2001 ; Marunteanu, 1999), the lack of most species representative for the NN7 Zone, and the monotypic development of H. carteri characterise the nannoplankton boundary. On the base of coccolith association with Braarudosphaera bigelowii and Perforocalcinella fusiformis, the environment appears to have more a near-shore character with lower salinity (river input). In the upper part of the columns, in the SW and S part of Mt. Medvednica a nannofossil community, belonging to the Catinaster coalithus - NN8 Zone was recognised. The first occurrences of Catinaster coalithhus and Ca. calyculus characterise this zone. It consist of Coronocyclus nitescens, Discoaster broweri, D. challengeri, Reticulofenestra minutula, Scyphosphaera apsteinii, Sphenolithus abies, Sph. neoabies, Syracosphaera pulchra. The communication with other part of Paratethys and Tethys oscillated through the Sarmatian and finally closed at its end.

calcareous nannofossils; paleoecology; biostratigraphy; sarmatian; Paratethys

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