International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

From continental platform towards rifting of the Tisza Unit in the Late Triassic to Early Cretaceous

Pages: 279 - 290

Authors: GÉZA CSÁSZÁR, BALÁZS SZINGER, OLGA PIROS

Abstract: The Upper Triassic—Lower Cretaceous successions of the Transdanubian part of the Mecsek and Villány- Bihor Zones of the Tisza Unit have been studied from the lithological, lithostratigraphical, sedimentological, microfossil and microfacies points of view in order to correlate and interpret the significant differences between them and to draw a conclusion about their geological and paleogeographical history. After an overview of the paleogeographical recon- structions of the broader area, the succession of the Mecsek and Villány-Bihor Zones and the debated Máriakéménd-Bár Range are introduced. Until the end of the Middle Triassic the study area acted as an entity. The first fundamental difference between the two zones can be recognized in the Late Triassic when marine carbonates were replaced by thick fluvial siliciclastics in the Mecsek Zone, while it is represented only by small, local lenses with a few and thin dolostone intercalations in the Villány Zone. The Mecsek Zone is bordered southward by one of the large listric faults to the north of which very thick siliciclastics developed in the Early to Middle Jurassic, whereas it is highly lacunose in the larger western part of the Villány-Bihor Zone. The break at the base is subaerial, higher in the succession it is shallow subma- rine. The sediment is silty, occasionally sandy crinoidal limestone of late Early Jurassic or even Middle Jurassic in age. The Upper Jurassic in the Mecsek Zone is composed of deep-water cherty limestone while in the Villány Zone it became a thick, shallowing pelagic limestone with reworked patch reef fragments. It is clear evidence that the Mecsek Zone had a thinned continental crust thanks to the nearby rift zone while in the Villány Zone the crust remained thick. The actualized version of the Plašienka’s paleogeographical model (Plašienka 2000) is introduced.

Keywords: Upper Triassic, Lower Cretaceous, Tisza Unit, rifting, facies analysis, plate tectonics, paleogeography, lithostratigraphy

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