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Triassic environments in the Circum-Pannonian Region related to the initial Neotethyan rifting stage

The present review provides an explanation to the Triassic sheet of the “Tectonostratigraphic terrane and paleoenvironment maps of the Circum-Pannonian region” series. Five multiple composite terranes (named herein as megaterranes) are distinguished in the region regarding their Variscan and Alpine evolution: ALCAPA (including the Gemer—Bükk—Zagorje Composite Terrane at its southernmost part), Dacia, Tisia, Adria—Dinaria and Vardar. We present in this review their Early Alpine/early Neotethyan evolution, beginning with the Middle Permian transgression on the eastern part of the Carnic—Dinaridic microplate, which gradually reached the Peritethyan region by the early Middle Triassic (except some parts of the Dacia Megaterrane), when intense carbonate production started. The Neotethyan oceanic rifting began in the Middle—Late Anisian by the disrupture and break-down of the Steinalm-type carbonate ramp. However, establishment of new oceanic crust has been proven as Late Anisian (Gawlick et al. 2008). In the Ladinian the paleogeographical pattern of the Neotethys NW-end became fully established: an oceanic domain in the middle, and its continental margins: the European or Carpatho-Balkanide developed on the Variscan Mediterranean Crystalline Zone and on the continuation of the Moldanubian Zone, and the Adriatic one (most part of the Adria—Dinaria Megaterrane) developed on the Variscan Carnic—Dinaridic microplate. The Early-Middle Anisian carbonate ramp stage was ended by a drowning event in the Late Anisian. It was followed by development of an articulated see-bottom, when platforms (Wetterstein-type) and basins (Reifling and Buchenstein Formations) came into being on both margins. Additionally, as the main difference against the European margin, on the Adriatic margin Anisian synsedimentary tectonic movements resulted in emersion and erosion of certain blocks, marked by Richthofen-, Uggowitz- and Otarnik-type conglomerates and breccias, that were followed by intense, controversially interpreted (island arc or early rift type?), mainly calc-alkaline volcanism with the paroxism in the Ladinian (formerly called in the Dinarides as “Porphyrite-Chert Formation”). During the Carnian ”Raibl or Lunz event”, related to humid climate, the basins in between the Wetterstein platform became filled up mainly by siliciclastics and on the smoothed surface intense carbonate production (Dachstein Limestone, Main Dolomite) took place from the Late Carnian till the end of the Triassic (which continued on large parts the Adriatic—Dinaridic Carbonate Platform till the end of Mesozoic). Well-expressed facies polarity shown by the gradual Neotethyan transgression from the Middle Permian to the earliest Middle Triassic and by Late Triassic facies zones (Hallstatt/Bódvalenke Limestone on the distal drowned part of the continental margin → Dachstein Limestone with reef facies on the outer shelf zone→ Hauptdolomit or Main Dolomite on the inner shelf zone → Carpathian Keuper or Keuper-like continental siliciclastics in the Peritethyan zone) is the best indicator of the existence of displaced/exotic terranes in the Circum-Pannonian region, regarding especially the two sides of the Periadriatic—Balaton and Zagreb—Zemplín or Mid-Hungarian lineaments. Thus, the Pannonian basement represents a school/textbook example of such kind of terranes, brought about mainly by sizeable Tertiary (pre-Middle Miocene) strike-slip and rotational displacements, respectively dispersions. However, at the NE border of the Gemer—Bükk—Zagorje Composite Terrane the lateral displacement, regarding dispersed remnants of the Hallstatt—Meliata zone, should have preceded the Cretaceous nappe stacking. The Bosnian—Serbian sector in the southern part of the Circum-Pannonian region represents the NW-most part of the complex Neotethyan suture zone(s). Further to the N, respectively NW and NE only small fragments (representing typical examples of disrupted terranes) of the Neotethyan accretionary complexes can be found in the area of the ”Carpathian loop” (Zagorje—Bükk/Darnó and Meliata Units, Transylvanides), dispersed due to late Mesozoic to Tertiary tectonic movements ; a fact, which cannot be neglected in Early Mesozoic paleogeographical reconstructions.

Circum-Pannonian Region, Alps. Carpathians, Dinarides, Pannonian Basin, Triassic, Neotethys, tectonostratigraphic terrains, paleogeography

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