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Palynology of a New Lower Pannonian (Upper Miocene) Reference Section from the Transylvanian Basin (Romania)

The Transylvanian Basin located in the eastern segment of the Pannonian Basin System (PBS) provides an ex-cellent insight into the early evolution of Lake Pannon. Lower Pannonian deep- water deposits, which are often buried deep in the Hungarian and Croatian part of the PBS are exposed on the surface. Despite the stratigraphic significance and rich fauna, a systematic palaeontological and biostratigraphic evaluation, including palynology, has not been carried out yet. The detailed multiproxy analysis (palaeontology including palynology, magnetostratigraphy and authigenic 10Be/9Be dating) of the Guşteriţa section fills a significant gap in the chronostratigraphic assessment of the Pannonian stage in Transylvania.The Guşteriţa clay pit near Sibiu exposes a continu-ous deep-water lower Pannonian section. The outcrop en- compasses a 55 m thick section of grey laminated or mas-sive marl and silty marl layers with fine-very fine-grained cross- laminated sand intercalations. The section hosts a rich fossil assemblage, including molluscs, ostracods, thecamoe-bians, fish teeth, otoliths, some partial fish skeletons, and fossil plants.Besides molluscs typical for Congeria banatica beds, organic-walled microplankton assemblages with dinocysts in particular, represent a powerful tool for biostratigraphic subdivision within the PBS. After the connection to the Eastern Paratethys and the Mediterranean region ceased around 11.6 Ma ago, Lake Pannon was formed in the Cen-tral Paratethys area. The brackish-water conditions initiated a remarkable radiation among organic- walled dinoflagel-lates. The isolated evolution of these dinocysts resulted in rapid morphological changes, which formed the basis of several regional biozonation schemes developed for the Hungarian and Croatian part of the PBS (e.g., SÜTŐ-SZ-ENTAI, 2000 ; BAKRAČ et al., 2012).A total of 25 palynological samples have been collected from the uppermost 25 metres of the quarry. The samples reveal a moderately diverse, but excellently preserved di-nocyst assemblage and several other aquatic (acritarchs & green algae) and terrestrial palynomorph groups (spore & pollen). The majority of the dinocysts are endemic Panno- nian taxa, e.g. Spiniferites pannonicus, Spiniferites oblongus, and various species of the genus Virgodinium, Impagidini- um, and Pontiadinium. The Guşteriţa dinocyst assemblages resemble those of Spiniferites bentorii oblongus biozone and the Pontiadinium pecsvaradensis biozone from the Hungarian part of the PBS. The biostratigraphic correlation sug-gests an age range between 11.0 and 10.6 Ma. This age assignment agrees with the magnetostratigraphy that placed the section into the C5n.2n long normal polarity mag-netic chron (11.056-9.984 Ma, ATNTS2012). Similarly, the calculated age from authigenic 10Be/9Be isotopic dating provided an age of 10.84 ± 0.4 Ma.The large amount of terrestrial palynomorphs and re-worked older Miocene taxa (e.g., Polysphaeridiumzoharyi, Cleistosphaeridiumplacacanthum and Melitasphaeridiumsp.) indicates intense erosion and runoff into the lake from the adjacent hinterland. Abundant bisaccate conifer pollen and Tsuga (hemlock) represent extrazonal vegetation elements originating pro- bably from the emerging mountains around the lake. Car-ya (hickory) and Tilia (linden) are characteristic elements of a warm-temperate mesophytic broad- leaved deciduous forests, while the high abundance of Taxodiaceae pollen indicates the presence of swamps along the shore. The new data also reveal the palaeogeographical con- nections between the Transylvanian Basin and other areas of the PBS which ceased by ca. 9 Ma ago. The integration of the new biostratigraphic subdivision with magnetostra- tigraphy and authigenic 10Be/9Be isotopic dating represent a significant improvement of the regional Pannonian chron-ostratigraphy and its correlation to the global time scale.

Neogene, Pannonian, Transylvanian Basin, bio- stratigraphy, palynology, dinoflagellates

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