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

KATER II Geology of the Rax-Schneeberg-region
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2.2 Structural frame of the Rax/Schneeberg aquifer system
The karstified plateau mountains of Rax and Schneeberg are forming the catchment areas of
several springs of the Vienna Water Supply, for example the Kaiserbrunn-, Hölltal, Fronbachand
Stixenstein spring.
The aquifer is mainly built by Middle to Early Upper Triassic carbonate rocks of shallow water
origin – the Gutenstein, Steinalm and Wetterstein limestones and dolomites. Limestones
from slope to basinal depositional sites – the Grafensteig limestones – are of some relevance
only in the northern Schneeberg area, see stratigraphic scheme Figs. 2 and 3.
SCHNEEBERG NAPPE
During the alpine tectonics this Wetterstein platform was detached from its basement and
from adjacent basinal carbonate rocks and became a tectonically isolated mass of rocks, the
Schneeberg Nappe.
The Lower Triassic Werfen Formation, which may act as an aquitard or aquiclude, was used
as a shear horizon during the nappe movements. Therefore only parts of it remained in the
stratigraphic succession of the Schneeberg Nappe, large parts got lost during thrusting. We
cannot expect it anymore as a continous layer below the carbonates.
The lateral boundaries of the Schneeberg Nappe can be drawn today without any doubt:
On the northern side the Triassic rocks of the Schneeberg Nappe are thrusted over Early to
Middle Jurassic basinal sediments of the Göller Nappe. The same situation is visible within
two tectonic windows, the Ödenhof- and the Hengst-Window.
On the western side the tectonic contact shows two different situations. In the northern part
the Schneeberg Nappe again superimposes Middle Jurassic basinal sediments of the Göller
Nappe. In the southern part Middle Triassic to Carnian rocks of the Schneealpe (Mürzalpen
Nappe) are dipping down toward east below the Schneeberg nappe.
On its southern side there is an overthrust contact to the Palaeozoic to Lower Triassic
shales and siliciclastics of the underlying Werfen Imbricates Zone. The tectonic nature of the
contact is proved by the intercalation of several slices of Middle to Upper Triassic rocks of
deep shelf and oceanic origin. An additional deformation has affected the southern margin of
Schneeberg nappe subsequent to the deposition of the Gosau-Group, resulting in recumbant
folds and backthrusting toward south.
On its eastern side the Schneeberg nappe is dipping down below transgressive Neogene
sediments of the Vienna basin, where it continues in the subsurface (proof by several oil
drillings).
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