A remarkable radiolarian assemblage from the Csővár area (Hungary) improves biostratigraphical correlation of the Rhaetian

Abstract

In the Csővár area of north‐central Hungary a remarkably well‐preserved Rhaetian radiolarian fauna, in which conodonts were also found, has enabled the identification of 49 radiolarian species belonging to 35 genera. The fauna is dominated by the orders Spumellaria and Entactinaria over less diverse Nassellaria. A taxon quantitative analysis and an extensive systematic description of the radiolarians is given. According to taxonomical and biostratigraphical evaluation of the fauna, the early Rhaetian age indicated by the radiolarians ( Proparvicingula moniliformis Zone, Assemblage 2, Subassemblage 2b) contradicts the conodont‐based late Rhaetian age ( Misikella ultima Zone). With the exclusion of reworking, the microfossil assemblage suggests an earlier first appearance datum (FAD) for Misikella ultima , that is below the Globolaxtorum tozeri radiolarian Zone. The obtained data strongly fit a similar occurrence from Japan. The issue is most likely to originate from the calibration of the Misikella ultima conodont Zone and the Globolaxtorum tozeri radiolarian Zone to the ammonoid zonations of the western Tethys and the eastern Panthalassa, respectively. The Tethyan zonal schemes of the Rhaetian either rely strongly on the semi‐restricted intraplatform Eiberg Basin, where Misikella ultima seems to show a false FAD, or are biased 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 correlation potential between Europe, Japan and western North America.