Identification of the North European Platform below the Eastern Part of the Western Carpathian Flysch Belt

Abstract

For the identification of the North European platform below the Western Carpathian Flysch belt and for the definition of the lithospheric and crustal relationships in the collisional zone between the Western Carpathian block and the North European platform, two migrated reflection seismic profiles with deep registration were chosen in the eastern sector of the Western Carpathians. Both of them were newly reprocessed (1999–2000), deep and composite seismic profiles, which define some new features in the geological structure in the eastern part of the Western Carpathians. From a general point of view, both seismic profiles are dominated by a fanwise (flowerlike) structure. However, we define this structure as fanwise, because in many features, it looks like a classic flower structure. The described fanwise structure has a great impact on the final form of the collisional zone. The impact of the fanwise structure is also clearly visible on both seismic sections in the area of the Inner Carpathian Paleogene basin. The Inner Carpathian Paleogene basin base dips moderately toward the Pieniny Klippen Belt in the northeast, and according to our interpretation of seismic lines, the Inner Carpathian Paleogene basin sedimentary package is divided into three or four structural levels (the oldest level is built up by basal Paleogene sediments, and the overlying folded Sambron Member beds consist of two structural levels and three structural levels [our opinion] of sediments; see mainly seismic section AB below). What is very interesting is that the uppermost level of the Sambron Member beds displays clear extensional features. The Pieniny Klippen Belt is a major tectonic unit at the surface, where it separates the Outer and Inner Western Carpathians. However, both seismic lines reveal that the Pieniny Klippen Belt has no continuous depth prolongation as a tectonostratigraphic unit. The seismic image allows an interpretation of an older subhorizontal structure of laterally wedging-out and interfingering rock units that originated by collisional processes in a wider zone associated with the Pieniny Klippen Belt. Younger and steep brittle structures that accompany the Pieniny Klippen Belt and its surroundings may be traced to great depths where they merge into a subvertical fault zone. This fanwise fault zone closely resembles a transpressional flower structure. From the point of view of hydrocarbon prospection, the most important feature of both seismic lines is the anticline structure of the North European platform below the thrust stack of the Flysch belt. This strong reflection package probably indicates the presence of carbonates in the North European platform cover (see seismic profile AB below). In our opinion, this structure is the most attractive for hydrocarbon exploration in the eastern part of the Slovakian Flysch Belt.