On the way to building the Norian conodont biozonation of the Circum-Pannonian Region

Conodont biozonation of the Norian (Upper Triassic) of the Western Tethys realm is in development from the 1970’s, however, a satisfactory scheme has not yet been established. The problem originates in the over-simplified taxonomy of Norian conodonts, since biostratigraphic investigations have never coupled with thorough and detailed systematic studies. Even the zonal schemes proposed after the millennium were based mainly on the species described in the second half of the 20^th century. Consequently, conodont zones of the existing schemes cover longer time intervals, although a finer subdivision would be possible. An ongoing research attempts to refine the Norian conodont biozonation of the Circum-Pannonian Region based on abundant conodont faunas of various localities.

The old trench at Mátyás Hill of the Buda Hills (Transdanubian Range, Hungary) exposes a ca. 20 m thick sequence of hemipelagic cherty dolostones of Lower to Middle Norian age. Dense sampling of the section yielded well-preserved conodont elements in high numbers. The lower half of the succession can be dated as Lower Norian (Lacian-3) based on the presence of Norigondolella navicula, Norigondolella hallstattensis and Ancyrogondolella ex gr. triangularis. In the upper half of the section, bedding is often disturbed, intervals of fractured blocks are common. Conodonts with morphological characters transitional to those of typical Middle Norian species first occur at the lower level of this interval, though Lacian forms remain dominant. This part represents the Lower-Middle Norian transition, which is often characterized by sedimentary breccias and/or fissure fills (e.g., Dovško section – Karádi et al., 2021; Kälberstein quarry section – Gawlick and Böhm, 2000). Species indicating inevitably Middle Norian age (Alaunian-1) were found 1.5 m below the top of the section where Lacian species are absent. This fauna is composed of Ancyrogondolella equalis, Ancyrogondolella ex gr. transformis and Mockina ex gr. matthewi.

Due to the large morphological variety and the very low number of figured specimens, the taxonomic revision of these Norian assemblages is yet to be done. Anyhow, the establishment of a high-resolution Norian conodont biozonation of the Circum-Pannonian Region seems feasible, which will allow a better correlation potential within the Western Tethys realm.

The research was supported by the National Research, Development and Innovation Office NKFIH PD-131536 grant.

 

References:

Gawlick, H.-J., & Böhm, F. (2000). Sequence and isotope stratigraphy of Late Triassic distal periplatform limestones from the Northern Calcareous Alps (Kälberstein Quarry, Berchtesgaden Hallstatt Zone). International Journal of Earth Sciences, 89, 108–129.

Karádi, V., Kolar-Jurkovšek, T., Gale, L., & Jurkovšek, B. (2021). New Advances in Biostratigraphy of the Lower/Middle Norian Transition: Conodonts of the Dovško Section, Slovenia. Journal of Earth Science, 32, 677–699.