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Paleogeographic characterization of the Early Cretaceous "Urgonian" carbonate platforms

Fekete K., Straka A.

Geology, Geophysics and Environment

2014

Vol. 40, no. 1

80--81

The objective of the present paper is to show clues which are provided for understanding the development and paleogeographic significance of the Lower Cretaceous carbonate platform sequences in different localities. The results are based mainly on the study of previous works and also on the preliminary results from lithological sections investigated by authors. The Urgonian-type limestone represents a characteristic Barremian and Aptian shallow-water carbonate facies deposited along the northern Tethyan margin. The term Urgonien was established by A. d'Orbigny in 1847 for the reef limestones near Orgon (southern France). The facies encloses massive, light-coloured organodetrital limestones with foraminifers (Orbitolina) and transitional sediments - detrital or siliceous limestones. Among bioclasts, fragments of bivalves (rudists), corals, hydrozoans, bryozoans, small and large foraminifera (Palorbitolina lenticularis, Sabaudia minuta) and algae are the most characteristic constituens. In the Early Cretaceous, the opening of Alpine Tethys was completed and induced the development of carbonate platforms on its northern margin. Urgonian carbonate platforms in the Tethys have been widely studied (e.g. Arnaud & Arnaud-Vanneau 1991, Michalik 1994). Several deposition areas can be distinguished in the Western Carpathians, mainly: the Tatric "Urgonian" Platform (biohermal and lagoonal facies), source of the detritus transported to the Murań Limestone; and the Manin Urgonian Platform prograding into the Bela Unit during the Aptian. Debris from both platforms was transported into adjacent basins and deposited as allodapic accumulations (Misik 1990). The oldest hypothesis on the position of the neritic "Urgonian" Lower Cretaceous limestones of the Manin Unit consisting of Podhorie and Manin formations was summarized by Andrusov (1938). He considered the Manin Unit as an independent nappe unit. Later, based on lithostratigraphic and tectonic features, he characterized it as a succession of Central Carpathian affinity. However, its position and the tectonic style are close to Pieniny Klippen Belt structures (Andrusov 1938, Birkenmajer 1977). From the Urgonian-like facies, which occur in the Klippen Belt and the Peri-Klippen Belt we focused mainly on the Manin Unit in the area of the Strazovske vrchy Mts., the Nizna Unit (Nizna Limestone Formation) (Jozsa & Aubrecht 2008), Benatina Klippe (Schlogl et al. 2004) and also in the Haligovce Unit (Haligovce Limestone Formation), which is usually considered as an equivalent of the Manin Unit. In the Outer Carpathians, the Urgonian-type limestones occur exclusively as exotic pebbles in younger deposits. Urgonian facies in the Western Carpathians shows some different features in comparison with other areas in the Tethys realm; e.g. lack of oolitic and oncolitic limestones, small representation of typical lagoonal facies with miliolids and dasycladaceans. The "reef-tufa" cementation, fenestrae, evaporate minerals are also missing, bauxitization is unknown. They use to be affected by silicification (presence of cherts). Dolomitization is almost missing (Misik 1990).