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

KATER II Geology of the Rax-Schneeberg-region
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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.
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