Late Jurassic tectonics and sedimentation: breccias in the Unken syncline, central Northern Calcareous Alps

Abstract

this study analyses and discusses well preserved examples of Late Jurassic structures in the Northern calcareous Alps, located at the Loferer Alm, about 35 km southwest of salzburg. A detailed sedimentary and structural study of the area was carried out for a better understanding of the local Late Jurassic evolution. the Grubhörndl and schwarzenbergklamm breccias are chaotic, coarse-grained and locally sourced breccias with mountain-sized and hotelsized clasts, respectively. both breccias belong to one single body of breccias, the Grubhörndl breccia representing its more proximal and the schwarzenbergklamm breccia its more distal part, respectively. breccia deposition occurred during the time of deposition of the ruhpolding radiolarite since the schwarzenbergklamm breccia is underlain and overlain by these radiolarites. Formation of the breccias was related to a major, presumably north-south trending normal fault scarp. It was accompanied and post-dated by west-directed gravitational sliding of the Upper triassic limestone ("Oberrhätkalk"), which was extended by about 6% on top of a glide plane in underlying marls. the breccia and slide-related structures are sealed and blanketed by Upper Jurassic and Lower cretaceous sediments. the normal fault scarp, along which the breccia formed, was probably part of a pull-apart basin associated with strike slip movements. On a regional scale, however, we consider this Late Jurassic strike-slip activity in the western part of the Northern calcareous Alps to be synchronous with gravitational emplacement of "exotic" slides and breccias (Hallstatt mélange), triggered by Late Jurassic shortening in the eastern part of the Northern calcareous Alps. Hence, two competing processes affected one and the same continental margin.Late Jurassic tectonics and sedimentation: breccias in the Unken syncline, central Northern calcareous Alps

Evidences for pre-orogenic passive-margin extension in a Cretaceous fold-and-thrust belt on the basis of combined seismic and field data (western Transdanubian Range, Hungary)

“…In this case, thickness variation of the pre-orogenic succession can be an indicator of synsedimentary normal faulting. The most characteristic fault-related sediments are coarse-grained talus-cone breccias (Ortner et al 2008); moreover, synsedimentary fault movements are often associated with soft-sediment deformation (Bergerat et al 2011).…”

Syn‐rift mass flow generated ‘tectonofacies’ and ‘tectonosequences’ of the Kingston Peak Formation, Death Valley, California, and their bearing on supposed Neoproterozoic panglacial climates

“…Large-scale faulting accompanied by earthquake activity and severe ground shaking is typically associated with the collapse of rock slopes in tectonically-active basins (Festa et al, 2016). Olistostromes of the Kingston Peak Formation are comparable with other known large faultgenerated megabreccia units of the Muya Rift of the Baikal Rift System (Ufimtsev et al, 1998), the faulted carbonate platform of the Devonian Yangshuo pull-apart basin (Chen et al, 2001), submarine fault scarps of the North Sea (McArthur et al, 2013(McArthur et al, , 2016 and the those within late Jurassic rifts of the Alps (Eberli, 1987;Ortner et al, 2008). The depositional setting of FA1 is thus envisaged as a deep water 'base-of-scarp' environment where material is shed abruptly by the catastrophic collapse of scarps cut into either hard bedrock or indurated basin-margin sediments, and transported en masse into deep water.…”

“…, 2013, 2016) and the those within late Jurassic rifts of the Alps (Eberli, 1987; Ortner et al. , 2008). The depositional setting of FA1 is thus envisaged as a deep water ‘base‐of‐scarp’ environment where material is shed abruptly by the catastrophic collapse of scarps cut into either hard bedrock or indurated basin‐margin sediments, and transported en masse into deep water.…”

Bulk inclusion micro‐zircon U–Pb geochronology: A new tool to date low‐grade metamorphism

“…The Austroalpine unit in the Eastern Alps is a nappe stack that was built from material of the Adriatic continental crust in the Cretaceous and then became the upper plate during the subsequent closure of the Alpine Tethys and collision of the European plate in the Cenozoic era (Figure 1a; Froitzheim et al, 2008;Schmid et al, 2004). Its tectonostratigraphic age is constrained by the synorogenic sediments on top of the cover nappes (140-100 Ma; Ortner et al, 2008) and by P-Tt-d data in the upper greenschist to eclogite facies nappes that together form a metamorphic extrusion wedge (100-85 Ma; Sölva et al, 2005;Tenczer & Stüwe, 2003;Thöni, 2006). The samples investigated in this study were collected at the base of the SHN, the upper structural level of the Austroalpine unit exposed in the Kitzbühel mountains north of the Tauern Window (Figure 1b, Pestal et al, 2005).…”

“…The samples investigated in this study were collected at the base of the SHN, the upper structural level of the Austroalpine unit exposed in the Kitzbühel mountains north of the Tauern Window (Figure 1b, Pestal et al, 2005). The nappe consists of (a) Neoproterozoic to Carboniferous metasediments and metavolcanics stacked together during the Variscan orogeny between 350 and 300 Ma (Heinisch et al, 2015), (b) a Permian to Jurassic cover sequence, and (c) Valanginian to Barremian (140-125 Ma) synorogenic sediments (Ortner et al, 2008). Alpine deformation and metamorphism documented by K-Ar and 40 Ar/ 39 Ar white mica ages commenced between 120 and 113 Ma and lasted until 90-95 Ma (Frank & Schlager, 2006;Kralik, 1983).…”