Radiolarians and Conodonts from Hungary (western Tethys) Improve Global Correlation of the Rhaetian

The Csővár area in north-central Hungary exposes blocks of the Mesozoic basement of the Pannonian Basin. In Late Triassic times the area was located at the western shelf of the Neotethys Ocean. During conodont biostratigraphic investigations on the Csővár Csv-1 core, one sample yielded a remarkably well-preserved Rhaetian (Upper Triassic) radiolarian fauna. The assemblage consists of 49 radiolarian species belonging to 35 genera. The fauna is dominated by the orders Spumellaria and Entactinaria over less abundant Nassellaria. For radiolarian biostratigraphy a North American zonation was used, as there is currently no global radiolarian zonation for the Rhaetian. The radiolarians indicate the lower Rhaetian Proparvicingula moniliformis Zone (Assemblage 2, Subassemblage 2b). The conodonts, however, suggest the Misikella ultima Zone of the upper Rhaetian, which is in contradiction with the radiolarian-based age. Reworking could be excluded by microfacies analysis. Since upper Rhaetian radiolarians were previously documented from the Csővár area, the issue cannot be explained by selective preservation of radiolarians. Consequently, the microfossil assemblage suggests an earlier first appearance datum (FAD) for Misikella ultima, that is below the upper Rhaetian Globolaxtorum tozeri radiolarian Zone. The obtained data strongly fit a similar occurrence from the Katsuyama section in Japan, where the conodont Misikella ultima was documented within the lower Rhaetian Deflandrecyrtium breviora radiolarian Zone of the Japanese Rhaetian radiolarian zonation, preceding the Globolaxtorum tozeri radiolarian Zone. The presence of Deflandrecyrtium breviora in the radiolarian assemblage from Csővár further supports the earlier FAD of the conodont Misikella ultima. The problem most likely originates from the calibration of the Misikella ultima conodont Zone and the Globolaxtorum tozeriradiolarian Zone with the ammonoid zonations of the Western Tethys and the Eastern Panthalassa, respectively. Establishment of the Misikella ultima Zone of the Western Tethys relied strongly on the semi-restricted intraplatform Eiberg Basin, where Misikella ultima seems to show a false FAD. Additional bias might have been caused by the insufficient data used for interregional correlation of different fossil groups. The newly obtained microfossils from the open marine succession of Csővár increase the global correlation potential, as they allow direct correlation between Europe, Japan and western North America. The research was supported by the National Research, Development and Innovation Office (NKFIH STARTING 149443 grant).