Explanatory notes to the digital geological map of the Rax ... - KATER

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KATER II Geology of the Rax-Schneeberg-region __________________________________________________________________________________________ LATE PLEISTOCENE TO HOLOCENE (12) - (1) Within the terminal moraine circle at Tränkwiese (north of Schneeberg) a completely flat area is supposed to represent late Pleistocene lake deposits (12). Also of late Pleistocene ages are two fluviatile fans (11) at Klostertaler Gscheid, which belong to an older drainage system. The recent one has changed its direction and is crosscutting the fans. Late Pleistocene to recent mass movements have created typical features like tension cracks (10), landslide scars (9), creeping soil/debris (8) and blocky debris (7) of rock fall. Recent deposits are slope debris and debris fans (6) at the foot of steep mountain slopes, fluviatile fans (5) from tributary valleys, swamp/moor deposits (4) and recent fluviatile gravel (2) and erosional features (3). Anthropogene deposits (1) are mainly caused by former mining activities (Iron ores). 17

KATER II Geology of the Rax-Schneeberg-region __________________________________________________________________________________________ 2 TEKTONIK 2.1 Principles of NCA structural evolution The sequence of Mesozoic sediments of the NCA has lost its former crustal basement during Alpidic Orogeny. During Upper Jurassic to Tertiary times several events of folding, gravitational gliding, thrusting and final faulting have created a complex pile of nappes which rests in the north with overthrust contact on the Rhenodanubian Flysch Zone and in the south with a tectonically disturbed transgressiv contact on the Greywacke Zone. The following nappe scheme of Northern Calcareous Alps can be given today: The northern (=frontal) part of the NCA (outside of the project area) is built by the Bajuvaric nappes, which one show narrow synclines and anticlines. They dip down toward the south below the overthrusted Tyrolic nappe system. Due to their widespread rigide dolomitic lithology the Tyrolic nappes exhibit internal thrusting and faulting and only minor folding. The southernmost nappe is the Göller Nappe with a stratigraphic succession from Triassic shallow water carbonates to Jurassic red limestones, marls and radiolarite. The Juvavic Nappe System represent the uppermost tectonic element, overlying Mesozoic rocks (Tyrolic Göller Nappe) in the north and the Greywacke Zone and its transgressiv Permoscythian cover (Werfen Imbricates Zone) in the south. It can be subdivided into a few large units (up to tens of kilometers), the Mürzalpen Nappe, Schneeberg Nappe, Hohe Wand Nappe and several smaller ones (hundreds of meters to about a kilometer), forming Klippen below or outliers above the larger ones. The contact between NCA and Greywacke Zone was a matter of long lasting controversial discussions: on the one hand there is a transgressive contact of Permo-Skythian clastics over Lower Palaeozoic rocks of the Greywacke Zone visible; on the other hand the Skythian clastics (Werfen Fm.) are followed by Middle Triassic carbonates. Many authors have seen here an undisturbed sedimentary sequence. Local missing members of the sequence have been explained by only minor thrusting. Other authors claimed that this sedimentary contact is only a virtual one. They postulated a major overthrust, separating the Permoscythian of a Tyrolic nappe system from carbonates of the Juvavic Nappe System – see PLÖCHINGER 1996, TOLLMANN 1985. This question is crucial for prediction of the deep subsurface structures, especially of the position of the aquifer/aquiclude boundary. New mapping of this southern margin has revealed a clear evidence for the overthrust concept. The thrust plane is marked by slices and small Klippen-like bodies of tectonized Middle to Upper Triassic rock sequences of the Hallstatt realm and of the Meliata realm - see MANDL & ONDREJICKOVA 1993, KOZUR & MOSTLER 1992. In this sense the Noric-Tyrolic Nappe System consists of the former Palaeozoic basement (Greywacke Zone) and the relictic preserved transgressiv Permotriassic (Werfen Imbricates Zone) of the Tyrolic Nappes. In the eastern NCA it has been left behind several kilometers in the south during the nappe movements. Today there is a common agreement that the NCA depositional realm during the Permotriassic was a passive continental margin between Variscian (=Hercynian) consolidated Pangäa and the Tethys ocean – see HAAS et al. 1995. Beginning in the Jurassic the Austroalpine realm (including the NCA) became separated from its European hinterland by the birth of the transtensional basin of the Penninic Ocean, which was linked by large transform faults to the opening of the Northern Atlantic Ocean. 18

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