Acta Geologica 38. (1995)

1. szám - J. Haas - A. Balog: Facies characteristics of the Lofer cycles in the Upper Triassic platform carbonates of the Transdanubian Range, Hungary

Acta Geologica Hungarica, Vol. 38/1, pp. 1-36 (1995) Facies characteristics of the Lofer cycles in the Upper Triassic platform carbonates of the Transdanubian Range, Hungary János Haas, Anna Balog Geological Research Group, Department of Geol. Sciences, Virginia Polytechnic Eötvös Loránd University, Budapest Institute and State University, USA Lofer cycles are metre-scale peritidal-subtidal (lagoonal) cycles within platform carbonates. Based on observations of Upper Triassic sequences of Lofer cyclicity in the Transdanubian Range, this paper summarizes fundamental features of the basic facies and subfacies which make up the cycles. Assumed environments of deposition of the distinguished facies types are also presented. Key words: carbonate platform, metre-scale cyclicity, facies analysis, paleoenvironment, peritidal, lagoonal, Upper Triassic, Transdanubian Range Introduction Due to their extension and thickness, Upper Triassic (Upper Carnian-Norian- Rhaetian) carbonate formations play a fundamental role in the construction of the Transdanubian Range. These particular formations, primarily the Main Dolomite (Fődolomit in Hungarian, which shows close similarity with the South Alpine Dolomia Principale and the Austroalpine Dachstein Dolomite, but differs from the typically bituminous, thin-bedded Hauptdolomit) and the Dachstein Limestone, extend far beyond the area of the Transdanubian Range. One can follow them all along the broad shelf of the former Tethys, from the West Carpathians, through the Eastern and the Southern Alps and also in the Dinarides and Hellenides. Even in the Himalaya and on Timor Island, the Upper Triassic formations show amazing similarity with the above-mentioned ones. The most spectacular feature of these platform carbonates is a meter-scale cyclicity, since, due to different colour and potential for weathering of the individual members of the cycles, this feature is well visible both in the natural outcrops and the quarry exposures (Fig. 1). Rapid and long-lasting subsidence of the Tethys shelf and development of an extremely broad and level tidal flat were particularly favourable for accumulation and preservation of thick cyclic peritidal-lagoonal sequences. Considering these facts it is understandable why these formations became classic examples of cyclic shallow marine carbonates, Addresses: J. Haas: H-1088 Budapest, Muzeum krt. 4/a, Hungary A. Balogh: Blacksburg, Virginia, 24061-0420, USA Received: 2 January, 1995 0236-5278/95/$ 5.00 © 1995 AkadémiaiKiadö, Budapest MAGYAR TUDOMÁNYOS AKADÉMIA KÖNYVTÁRA