Vol.:(0123456789) 1 3 International Journal of Earth Sciences https://doi.org/10.1007/s00531-018-1636-4 ORIGINAL PAPER Stratigraphic correlation and structural position of Lower Cretaceous fysch-type deposits in the eastern Southern Alps (NW Slovenia) Špela Goričan 1  · Lea Žibret 2  · Adrijan Košir 1  · Duje Kukoč 1,3  · Aleksander Horvat 1 Received: 3 December 2017 / Accepted: 9 July 2018 © Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract Lower Cretaceous syn-orogenic sediments derived from the obducted ophiolites of the Meliata–Maliac–Vardar (Neotethys) Ocean are typically found in the Dinarides and the Austroalpine units. Correlative fysch-type deposits linking both regions through the Southern Alps had been reported from the Bohinj area (NW Slovenia), but their stratigraphic and structural framework remained poorly known. Our research focused on stratigraphic and structural feld studies in a 50 km 2 area between Lake Bled and Lake Bohinj in the Julian Alps. The mixed carbonate–siliciclastic sediments, informally named the Studor formation, range in age from the Valanginian (possibly late Berriasian) to the Aptian. They occur on top of two dif- ferent stratigraphic successions, which we assign to two separate nappes. The frst succession consists of deep-water Middle Triassic to Lower Cretaceous deposits of the Bled Basin and belongs to the Pokljuka Nappe, which is the uppermost nappe of the Julian nappe stack. The second succession consists of Upper Triassic to Lower Jurassic platform carbonates and a thin Jurassic–Cretaceous deep-water sequence. This succession was deposited in the marginal area of the Julian Carbonate Platform/Julian High and now belongs to the underlying Krn Nappe. The original (Dinaric) thrust contacts between the Pokljuka and Krn nappes are obliterated by younger deformations. The present-day boundaries between these two nappes are steep NE–SW and younger NW–SE trending faults. The post-nappe deformation sequence characterizing the Alps–Dinarides transition zone has been recognized: (1) Oligocene–Early Miocene NW–SE contraction; (2) Early–Middle Miocene exten- sion; and (3) Late Miocene to recent inversion and transpression. Keywords Alps–Dinarides transition zone · Mesozoic stratigraphy · Geological map · Julian nappes · Post-nappe tectonics Introduction The eastern Southern Alps (including the Julian Alps in NW Slovenia) are part of a complex, more than 300 km long transition zone between the Alps and the Dinarides (Fig. 1). An overlap of the Dinaric and younger Alpine structures was frst recognized westwards in the eastern Southern Alps of northern Italy (Doglioni and Siorpaes 1990) and then also confrmed at the boundary between the Southern Alps and the Dinarides in Slovenia (Placer and Čar 1998). Recent studies revealed that the zone of interference extends far eastwards to the Internal Dinarides in northern Croatia (van Gelder et al. 2015). The nappe system in the research area was derived from the continental margin of the Adriatic microplate. In the Middle and Late Jurassic, this part of the margin was located between two oceanic domains: the Alpine Tethys and the Meliata–Maliac–Vardar branch of the Neotethys (in the sense of Schmid et al. 2008). In complex transition zones, key segments with a solid stratigraphic and structural framework may help considerably in understand- ing the broader area. The primary aim of this study is to clarify the structural position and hence tectonic emplacement of Lower Creta- ceous fysch-type deposits that occur in the eastern Julian Alps. Time-equivalent syn-orogenic sediments are common Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00531-018-1636-4) contains supplementary material, which is available to authorized users. * Špela Goričan spela@zrc-sazu.si 1 Ivan Rakovec Institute of Palaeontology ZRC SAZU, Novi trg 2, 1000 Ljubljana, Slovenia 2 Research and Development in the Field of Natural Sciences, Lea Žibret s.p., Černetova ulica 3A, 1000 Ljubljana, Slovenia 3 Croatian Geological Survey, Sachsova 2, 10000 Zagreb, Croatia