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

TECTONIC STRUCTURE OF THE KIS-FENNSIK AREA (BÜKK MOUNTAINS, NE HUNGARY)

Pages: 223 - 234

Authors: MARTON FORIAN-SZABO, LASZLO CSONTOS

Abstract: Stratigraphic and structural investigations based on geological mapping in the Kis-fennsik region (NE part of the Bükk Mts, NE Hungary) proved the complex nappe structure of the area. According to new biostratigraphic data and structural setting, three main tectonostratigraphic units can be distinguished: in lowest structural position Carboniferous to Triassic deposits of the Bükk Parautochthonous Unit are forming a huge south-vergent anticline (North Bükk Anticline NBA). The Szarvaskő-type Harica Nappe (HN, representing the upper part of the Jurassic) is thrust over the northern limb of the anticline. After the emplacement of the Harica Nappe, Middle-Upper Triassic rocks of the North Bükk Anticline (Szeleta sliver, NBA/b) are thrust onto the HN unit, and along an E-W striking thrust fault onto the older part of the NBA unit. In the southern part of the investigated area a narrow zone of platform carbonates and dark shales (Vesszős Formation) was mapped. Together with the overlying thick cherty limestone succession, they are considered to belong to the NBA/b unit. All the above mentioned units, affected by regional dynamothermal metamorphism, are overlain by the Kisfennsik Nappe (KN), which consists of slightly metamorphosed Carnian platform limestones and dolomites, with some intercalating metavolcanites. Emplacement of the thrust sheet to the SE resulted in small- to map-scale folding in the North Bükk Anticline. Thrusting is attributed to the Cretaceous tectonometamorphic evolution of the Bükkium. Later, an intensive shortening generated well-developed, NE-SW oriented antiform-synform structures with reverse faults in all units. Folds with NW-SE axis represent another deformation phase.

Keywords: Bukk Mts, Kis-fennsik, geological mapping, Northern Hungary, tectonostratigraphy, deformation

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