Geologica Hungarica - Series Palaeontologica 55. [antikvár]

Geologica Hungarica series Palaeontologica, fasciculus 55 INTRODUCTION Attila Vörös The Balaton Highland is one of the most renowned and important reference areas of the Alpine-Tethyan Triassic stratigraphy (see Tozer 1984). Especially the Middle Triassic strata of this region became famous very early, in the 1870's, due to the magnificent pioneering works by Böckh (1872, 1873) and Mojsisovics (1873, 1882). One of the stratigraphical highlights was the "Trachyceras Reitzi horizon" whose importance is still acknowledged in the recent discussions on selecting the GSSP of the Anisian/Ladinian boundary. Another formation proving to be of outstanding importance was the "Muschelkalk" with "Ammonites Balatonicus". This ammonoid species, lending its name to one of the earliest described Middle Triassic genera (Balatonites Mojsisovics, 1879), is still the best marker of the substage now called Pelsonian (the middle Substage of the Anisian Stage). The first official naming of this substage as "Balatonisch" performed by Mojsisovics, Waagen Diener (1895) was a kind of tribute to the Balaton Highland. The next effort to contribute to the knowledge of the Pelsonian of the Balaton Highland is connected to the ambitious international project entitled "Wissenschaflliche Erforschung des Balatonsees" (Scientific Research of the Lake Balaton) lead by L. Lóczy sen. at the turn of the twentieth century. The product was a series of monographs which incorporated some very important stratigraphical (Laczkó 1911) and palaeontological (e.g. Diener 1899 and Arthaber 1903) contributions and was complemented with a comprehensive closing volume (Lóczy 1913, 1916). In the next decades, regrettably little progress was achieved in the research of the Middle Triassic of the Balaton Highland. Perhaps by this reason, PiA (1930, figs 2, 3), when introducing the substage name "Pelson", clearly referring to the Roman name of the Lake Balaton (Lacus Pelso), indicated the Dont valley as type section. In the 1960-1970's, Imre Szabó made extensive field work and stratigraphical research at the Balaton Highland, but only a minor part of this voluminous knowledge was published (Szabó 1972, Szabó et al. 1980). The pressing interest by the international scientific community {e.g. Assereto 1969, 1971; Workshop Meeting on IGCP Project 4., 1978) clearly indicated the necessity of new studies and an updated synthesis regarding the Triassic stratigraphy of the Balaton Highland. The review papers by Detre (1974, 1975) underscored some of the problems but did not fill the gap of knowledge. In the last two decades, important excavations and boreholes have been established at the Balaton Highland in the scope of the state-financed Geological Key Section Programme, coordinated by J. Fülöp and J. Haas. On this ground — partly connected to the detailed geological mapping project by the Geological Institute of Hungary (MÁFI — led by Géza Császár and Tamás Budai), partly sponsored by the National Scientific Research Fund (OTKA) — we have made detailed collections in many important stratigraphical sections and greatly improved the Middle Triassic stratigraphy of the Balaton Highland. The results have been integrated to the comprehensive volume on the geological mapping (Budai et al. 1999a) and to handbooks (e.g. Haas et al. 2001). Part of these results contributed to the recent resurgence in the "Anisian/Ladinian boundary problem" (Vörös 1993, Vörös et al. 1996, 2003). The other part of the new results was mainly connected to the Pelsonian strata; some of them were published in preliminary contributions (Vörös 1987, Tatzreiter & Vörös 1991). In the last years, a special grant by the National Scientific Research Fund (OTKA, T 26278) was dedicated to the updated synthesis of stratigraphy and a redefinition of the Pelsonian Substage at the Balaton Highland. In the course of our work we have made new, detailed, bed-by-bed collections of fossils and samples. The new data were integrated with the available, previous knowledge into a coherent data base. The main purposes were the biostratigraphical subdivision and definition of the Substage with designation of its boundaries and the description of its lithological and palaeontological content. The present volume is intended to sum up the recent knowledge on the Pelsonian Substage at the Balaton Highland. The first chapter, written by T. Budai and A. Vörös is a concise introduction to the geological setting of the Balaton Highland and the general relationships of the Pelsonian formations.