Middle Norian conodonts from the Buda Hills, Hungary: an exceptional record from the western Tethys

Abstract

Recent biostratigraphic investigations of pelagic dolomites in the Buda Hills area, Hungary provided unique Middle Norian conodont assemblages. Due to the poorly represented Tethyan record of similar faunas and the present state of our knowledge of Alaunian conodonts, finer age assignment could not have been carried out. The purpose of this study is to discuss the natural cause (sedimentary, tectonic and paleoecological) and artificial biases (lumping taxonomy and inadequate figuration) that led to a scarce representation of the Alaunian conodont record. Further aims are to present here several taxonomic, systematic, and biostratigraphic notes on the Middle Norian conodonts based on the rich material recovered. Rock samples were processed using standard dissolution technique of dilute acetic acid. Scanning micro-photographs were taken of the conodont specimens from three views. Remarks are added to the problematic species Epigondolella abneptis and Mockina postera, and some aspects for improvement of the Middle Norian conodont biostratigraphy are suggested. Detailed systematic descriptions of 3 genera and 15 species are given. The observed faunas include 5 previously unknown forms, namely Epigondolella aff. vialovi, Mockina aff. matthewi, M. aff. postera, M. aff. spiculata and Mockina sp. A. The Tethyan occurrence of Epigondolella transitia, a transitional Lower/Middle Norian conodont species previously known only from North America, is documented. The assemblage lets an insight into the main characteristics of the Lacian/Alaunian faunal turnover and into the evolutionary trends that resulted in the origination of the last representatives of conodonts of the Sevatian and the Rhaetian. The new conodont record of the Buda Hills highlights the fact that Alaunian conodonts are less known among Upper Triassic faunas. This work suggests the route of the future studies for a more precise and global applicability of conodonts in the Middle Norian biostratigraphy.