8th International Nannoplankton Association Conference


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Carmen M. Chira, Mariana Marunteanu:
Calcareous nannofossils and dinoflagellates from the Middle Miocene of the Transylvanian Basin, Romania

Geological setting The study is focused on the Middle Miocene (Badenian, Sarmatian and Pannonian pars.) calcareous nannofossils and calcareous dinoflagellates from the Transylvanian Basin, and also the Mures Passageway which represented the connection between the Transylvanian and the Pannonian Basins. Some of the most representative sections have been especially refered to.

The calcareous nannofossils and calcareous dinoflagellates from the fossiliferous site, Lapugiu de Sus (Mures Passageway: Badenian), and also from Livada, Dej and Ciceu Giurgesti (Badenian), Dej, Sibiu (Sarmatian), Sibiu, Baia Mare (Pannonian: Transylvanian Basin) and other areas, have been analysed.

Nannofossil assemblages and calcareous dinoflagellates The Badenian calcareous nannofossil assemblages of the Transylvanian Basin belong to Biozones NN5 and NN6. A succession of bioevents was observed and the regional Badenian substage was better defined. The Moravian is characterised by NN5, its lower boundary being marked at the last occurrence of Helicosphaera ampliaperta and locally being approximated at the first occurrence (FO) of Discoaster exilis. The Wielician can be correlated with the top of NN5 and the lowermost part of NN6, containing the interval between the FO of Discoaster brouweri or of Helicosphaera wallichii and the FO of Helicosphaera stalis. The Kossovian corresponds to the most part of NN6, its upper boundary being marked by the extinction of Cyclicargolithus floridanus.

Detailed previous studies of the Badenian calcareous nannoplankton from the entire Carpathian area in the territory of Romania suggest the following correlation between the regional and global chronostratigraphic units: the Moravian, characterised by the Geminilithella rotula Subzone, NN5a, corresponds to most of the Langhian (except the lowermost and uppermost parts); the Wielician, characterised by the Helicosphaera wallichii, NN5b, and Discoaster variabilis, NN6a, Subzones, can be correlated with the uppermost Langhian and the lowermost Serravallian; the Kossovian, characterised by the Syracosphaera histrica, NN6b, Syracolithus dalmaticus, NN6c, and Calcidiscus pataecus, NN6d, Subzones, corresponds to the Lower Serravallian.

The Lower Badenian nannofossil assemblages from the Mures Passageway (Lapugiu de Sus) are some of the richest and well-preserved of this age; very rich and representative nannofossil assemblages of this age have been found also at Livada, among other areas. The calcareous nannofloras from the Lapugiu de Sus area contain the species which characterise NN5, and especially NN5a. In the Lapugiu Valley, only NN5a was noted but in the Cosu Valley, almost the entire NN5 is present. At Livada, the nannofossil assemblages are assigned to NN5.

From the stratigraphic distribution of the species, a series of local bioevents have been observed in the Lapugiu Valley: Cyclicargolithus abisectus has its LO simultaneously with the LO of Discoaster deflandrei. The FO of Rhabdosphaera pannonica was noted in the upper half of the subzone.

The nannofossil assemblages have been studied both by light and by electron microscope. Most species of the nannofossil assemblages prefer warm, tropical waters.

In the Lapugiu Valley section, it was noted that the frequency of Discoaster species is 'normal' in the lower part of the sedimentary succession and rare in the upper part. This probably reflects a diminution of temperature in the interval of deposition of the upper part of the Moravian succession. At Lapugiu de Sus, the calcareous dinoflagellates (calcispheres) Thoracosphaera heimii and T. deflandrei were frequently found. Also, fossil ascidian spicules, which prove tropical waters to have been rich in carbonate, were present. At Livada, Thoracosphaera spp. and Scyphosphaera apsteinii were found. Thoracosphaera and Scyphosphaera spp. are present also in others sections in Badenian deposits.

The Sarmatian calcareous nannofossils have been considered to include NN7, NN8 and NN9, although only NN6 pars. and NN7 have been found in the Sarmatian of the Central Paratethys previously. NN8, NN9, NN10 and NN11 pars. are considered characteristic for the Pannonian. Observations regarding the Sarmatian nannoplankton made for the deposits from Lower Austria and Burgenland are valid also for the majority of the other basins of the Central Paratethys, in our case, the Transylvanian Basin: lack of useful guide-fossils precludes the correlation with the standard nannoplankton zonation.

The characteristics of the Sarmatian calcareous nannofossils from Romania have been mentioned for the Volhynian-Lower Bessarabian interval previously by Marunteanu: the assemblages are dominated by species of Braarudosphaera, Calcidiscus, Coccolithus, Helicosphaera, among others, which represent the assemblages described from the entire Central Paratethys by numerous authors; there is a great number of individuals but a small number of species; there is an explosive development of Calcidiscus leptoporus, Calcidiscus macintyrei, Braarudosphaera bigelowii and Reticulofenestra pseudoumbilicus; the existence of the species Rhabdosphaera pannonica and Rhabdolithus poculi, mentioned only from the Central Paratethys; the extinction of Calcidiscus pataecus in the lower part of the deposits considered of the Lower Bessarabian and of Rhabdolithus poculi in the upper part of the Volhynian deposits; the FO of the species Calcidiscus leptoporus centrovalis in the lower part of the deposits considered as Lower Bessarabian. These characteristics influenced Marunteanu to name these assemblages as assemblages of Pannonian Basin-type, although they do not fit exactly into Matrini's standard zonation. In the Sarmatian deposits, rare specimens of Thoracosphaera saxea, T. albatrosina and T. deflandrei were also found.

Calcareous nannofossils are scarce in the Pannonian deposits of the Transylvanian Basin, which are restricted in the southern part of the basin. The Pannonian deposits from the Transylvanian Basin contain strongly endemic nannofossils, represented by different species of Noelaerhabdus and Bekelithella. In conformity with the nannoplankton biozones, separated in the Pannonian area, the Pannonian nannoplankton assemblages identified in the Transylvanian Basin belong to the Noelaerhabdus bozinoviciae and Noelaerhabdus bonagalii Biozones. The first biozone (with Noelaerhabdus bozinovicae, N. jerkovicii, N. tegulatus and very rare specimens of Coccolithus pelagicus, Calcidiscus leptoporus, Braarudosphaera bigelowii) characterises the Pannonian C-D and can be correlated with upper NN9 and lower NN10 (Late Bessarabian-Chersonian in age, in the Oriental Paratethys). The second biozone (with Noelaerhabdus bonagalii, N. mehadicus, N. bozinoviciae, N. jerkovicii, Bekelithella echinata, Bekelithella sp.) characterises the Pannonian E and corresponds to NN10 (upper part)-NN11 (lower part) (Early Meotian in age in the Central Paratethys). In the Upper Bessarabian-Lower Meotian deposits, Thoracosphaera and Scyphosphaera are frequent species.


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