engleski

The Sarmatian Paleoecology based on diatoms and calcareous nannoplankton (Kostanjek, Mt. Medvednica, Croatia)

On the SW slope of Mt. Medvednica, a 1.5m thick geological column Kostanjek, composed of upper part of Sarmatian strata (which belonges to NN8 zone of calcareous nannoplankton), was investigated on phytoplankton. The boundary with pannonian stage is comform. Fossil material is poor and include rare fish vertebrate and scales, macro (gastropods, bivalves) and microfauna (ostracods, foraminifera), macroflora casts, siliceous microfossils (diatoms) and calcareous nannoplankton. The succession consists of alternated light and dark thin layers of varves (0, 5 – 2 mm, max. 4 mm thick). They are indicators of seasonal changes in climate. Salinity and temperature are also depended on climate. Stratificated marine basin system, on the beginning of the column, has been represented by assemblage of marine to freshwater plankton diatoms (Actinocyclus roperi, Coscinodiscus plicatus, C. rugulosus, C. sarmaticus, Melosira dickiei var. fossilis). In the middle part of the column, because of mostly monofloristic abundance of diatom species Thalassionema nitzschioides the salinity was lower (~23 ‰ ). At the end of the column the number of species are dropped and bentic, Lake Forms of freshwater diatoms prevailed (Cymbella cf. ventricosa and Nitzschia sinuata var. tabellaria), because of near shore influence and/or locally closer of the basin. These two species are found for the first time in this part of Paratethys. The presence of calcareous nannofossils (Coccolithus pelagicus) and diatom species (Coscinodiscus sarmaticus, Thalassionema nitzschioides) in samples, suggest variations in temperature (3 - 27°C) which are common in more temperate climate area. The sedimentation was generated from suspension in low energy environment (bentonite clay), and many species from Eocene (calcareous nannofossils), lower Miocene (diatoms and calcareous nannofossils) and Badenian (calcareous nannofossils) are found in it. Our part of Paratethys belongs to boreal Sarmatian Sea with regressive trend.

calcareous nannoplankton; diatoms; younger Sarmatian; temperate climate; Croatia; Paratethys.

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