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Correlation between Paratethys-Mediterranean (NN-MNN)calcareous nannoplankton zonations.

In many cases standard Sarmatian i.e. Serravalian to Tortonian zonal calcareous nannoplankton species are absent or rare in sediments of Paratethys and Mediterranean region. The problem appears when the Paratethys calcareous nannofossils zonation (on assemblage, abundance and appearance on a certain species/genera level) tries to correlate with Mediterranean that is in some cases different. The Badenian/Sarmatian boundary is determined on the base of specific development and appearance of certain species/genera in Central Paratethys. Specifically, near the top of NN6 zone i.e. near the base of NN7 zone, Cyclicargolithus floridanus decreases in abundance or disappears and is replaced by abundant large R. pseudoumbilicus (≥ 7 μ m) in the assemblage (Perch-Nielsen, 1985). This event is marked, in some other basins at different stratigraphic levels (Raffi et al., 1995). The last occurrence (LO) of Cyclicargolithus floridanus is noticed somewhat earlier in the Mediterranean than in the Paratethys (Mărunţeanu, 1999 ; Hilgen et al., 2003). Its LO also differs between the Central and Eastern Paratethys. The first occurrence (FO) of Calcidiscus pataecus, which is significant for the Lower Sarmatian of the Croatian Basin, differs within the Paratethys too. Its FO in the Transylvanian Basin is characteristic for the end of the Badenian NN6d zone (Chira & Mărunţeanu, 2000) as in the investigated area (Slavonian Mts.). In the Vienna Basin FO of C. pataecus is noticed at the beginning of Sarmatian (S. Ćorić, pers. commun.). First rare appearance of Discoaster cf. kugleri in Mediterranean sapropel sediments (8, 05 m in thickness) is detected at 11, 88-11, 91 Ma (Ancona, Italy). Its last appearance is at 11, 6 Ma, (Hilgen et al., 2003). Based on astronomical data, the Serravalian/Tortonian boundary has been calibrated at 11, 6 Ma. Nevertheless, the last appearance/disappearance of Discoaster aulakos, Dis. deflandrei, and H. walbersdorfensis in the Mediterranean region is within the NN7 zone (Iaccarino et al., 2001). However, the investigations that have been done lately locate the last occurrence of H. walbersdorfensis species at 10, 74-10, 76 Ma (Hilgen et al., 2003), which is in contradiction with earlier mentioned duration of NN7 zone for the Mediterranean region. Radiometric analyses of the Central and Eastern Paratethys are given by Vass (1999), who made numerical calibration with Berggren’ s records (Berggren et al., 1995). Considering the rare occurrence of Discoaster kugleri species in sediments he placed the NN 7 zone between 11, 85 – 11, 3 (10, 9) Ma. In the North Croatia Basin the LO of H. walbersdorfensis species is detected at the end of the Lower Sarmatian, which is also opposite to the mentioned facts but speaks in behalf of specific developments of the Paratethys. Catinaster coalitus, which FO defines the base of the NN8 zone, is rare or absent in many Mediterranean sections. The last occurrence of Coccolithus miopelagicus has been detected a little earlier (NN7/NN8 zone), before the first occurrence of Discoaster hamatus in the Mediterranean. So, the LO of Coccolithus miopelagicus could be taken as an alternative marker for the NN7/NN8 boundary (Marino & Flores, 2002). This event belongs to 'Chron C5r' (Hilgen et al., 2000) that happened at 11, 2 Ma based on astronomical data for the Mediterranean region (Aguilar et al., 2004). In the North Croatian Basin the LO of Coccolithus miopelagicus is also observed at the NN7/NN8 boundary. The FO of Catinaster coalitus in the Mediterranean is noted at 10, 73-10, 74 Ma (Hilgen et al., 2003). Radiometric analyses from the Paratethys (Poland and Eastern Slovakian Basin) placed the period between 11, 3-10, 9 Ma (Vass, 1999 ; Kováč et al., 2001). The first appearance of D. hamatus in the Romanian part of the Paratethys is found in the NN9 zone, which corresponds to Mediterranean Serravalian/Tortonian boundary (Mărunţeanu, 1999). This bioevent (FO of D. hamatus ) is in the Mediterranean set at 10, 15 Ma. The Serravalian/Tortonian boundary is put at 11, 6 Ma for the Mediterranean and low latitude ocean (Hilgen et al., 2003). Lack of reliable magnetostratigraphy data for the boundary interval in other regions could cause these misfits during the correlations. The reason for different appearance might also be in reduction of connection at the end of Sarmatian between the Mediterranean and Paratethys and their re-opening during the Pannonian. The future data on magnetostratigraphy using astronomical cycles as well could give us better understanding of those relations. The paleomagnetic measurements in Našice section (Slavonian Mts.) put the Sarmatian/Pannonian boundary at Chron C5r.1r, which corresponds to 11, 1 Ma (Agusti et al., 2001 ; Vasilev, 2006). It’ s obvious that the Sarmatian/Pannonian boundary for the Paratethys that has been previously placed at 11, 6 Ma needs to be revised.

Calcareous nannoplankton; biostratigraphy; Paratethys; Mediterranean

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