geological field trip to the northern calcareous alps

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ALPS 2016
1-8 SEPTEMBER
GEOLOGICAL FIELD TRIP TO THE NORTHERN CALCAREOUS ALPS
ALPS 2016
1-8 SEPTEMBER
Introduction
Die Zielsetzung unseres Projekts ist, unsere Studenten mit der Geologie der Nördlichen Kalkalpen
durch eine Geologische Feldübung bekannt zu machen. Diese mehrtägige Feldübung würde uns
eine gute Gelegenheit bieten, um die Ähnlichkeiten und die Unterschiede zwischen den
ungarischen und alpinen Gesteinen vor Ort zu studieren.
Die Sedimente der Nördlichen Kalkalpen wurden zwischen dem Ober-Perm und dem tieferen Jura
auf einem typischen passiven Kontinentalrand abgelagert. Die ältesten bekannten Gesteine sind
Mergel, Sandsteine und Schiefertone, die nur wenig deutlich hervortreten. Das größte Volumen der
Kalkalpen besteht aus Kalksteinen und Dolomiten aus dem Trias-Zeitalter. Die bekanntesten und
mächtigsten Formationen von ihnen sind der Hauptdolomit, der Wettersteinkalk und der
Dachsteinkalk. Diese Gesteine bauen auch die Mehrzahl der höchsten Gipfel der Kalkalpen auf, wie
zum Beispiel den Hohen Dachstein, den Watzmann und den Hochschwab. Die meisten
Schichtglieder des Jura sind Mergel, Kalke und kieselige Kalke, die in der Tiefsee abgelagert wurden.
Die Gebirgsbildung der Alpen startete im Jura, als das östliche Meeresbecken des Neotethys-Ozeans
sich zu schließen begann und sich der erste Deckenstapel entwickelte. Vom Kreide-Zeitalter an
wurde dieser jurassische Deckenstapel mehrfach tektonisch überprägt und verändert, und dabei
wurden die Nördlichen Kalkalpen durch tektonische Bewegungen an ihrem heutigen Platz
transportiert.
Die meisten wichtigen strukturellen Einheiten und Decken der Nördlichen Kalkalpen werden
während der Geländeübung besichtigt. Wir möchten auch Deformationsstrukturen, wie zum
Beispiel Deckenüberschiebungen, Falten und Verwerfungen ausführlich studieren, da solche in
Ungarn nicht oder nur in begrenztem Ausmaß beobachtbar sind. Deswegen ist es für die
ungarischen Studenten äußerst wichtig, diese Gesteine direkt im Gelände zu sehen, um die Bildung
und die Bedeutung dieser Strukturphänomene besser zu verstehen.
93öu4
Jurassic tectonics at Schesaplana, Vorarlberg (Rätikon)
Our first field day was dedicated to examine the
Jurassic tectonics at Schesaplana in Vorarlberg.
We strated at Melkboden (1620 m) where saw
some examples for early deformation in
calcareous sediments (slump). Then we walked
up through Oberzalimhütte to Mannheimer Hütte
(2679 m) while examined some nice examples
those Jurassic tectonics mentioned above.
Slump: early
deformation in
calcareous
sediment
N
S
Oberzalimhütte
S
N
N
Hau
S
ptd
olo
Köss
en
mit
N
Alg
äu
e
View from the Mannheimer Hütte
me
li
ät
rrh
e
Ob
View from halfway to Mannheimer Hütte:
T3: Kössen, Hauptdolomit, Oberrhät limestone,
J1: Algäu
n
sto
Krabachjoch Klippen, condensed sedimentary succession of Zürser Schwelle, Aptian to Cenomanian synorogenic sedimentary succession
On our second field day we walked to Trittalm, Gondelbahn Rüfikopf, Bockbachsattel and then
to Rauekopfscharte. In the Northeren Calcareous Alps the nappe stack is translated towards
the NNW, which caused the nappe units extending over the whole orogen. The shape of the
nappes are controlled by the occuring facies boundaries.
The thrust between the Lechtal and Inntal nappes was cut by previous folding. The Upper
Triassic Dolomites from the westernmost part of the Inntal nappe overlie the Cenomanian
synorogenic deposites. Since the Inntal succession was eroded down to the Upper Triassic
sequences, it contains no Jurassic sediments. This was caused by the Upper Cretaceous Gosau
groups synorogenic deposition. Therefore the Gosau was placed directly above the Haupt
Dolomite with an angular unconformity. This is the youngest part of the sedimentological
succession which was deposited in shallow marine environment.
Sunset view from
Stuttgarter Hütte
Inntal Upper Triassic cliffs placed on top of Lechtal Upper Jurassic
and Creatceous successions
Sequence boundary
Geometry of growth strata in a transpressive fold belt: Gosau Group at Muttekopf
Our third field day was dedicated to examine the large-scale geometries
of growth strata in transpressive settings at Muttekopf. The panoramic
views provided an excellent way to understand the different structures,
resulted geometries and their relationships. In general the thrust sheets
of the Northern Calcareous Alps were emplaced during Late Cretaceous
thrust-dominated transpression. Thrust sheet-top sediments were
deposited during thrusting and associated fold growth and were
controlled by active folding and tearing. Episodic tear fault activity may
create several angular unconformities attached to a tear fault.
View from the west of the Muttekopf syncline (centre) and the Larsenn
anticline in the ridge Muttekopf-Rotkopf.
N
Muttekopf
Uppe
S
r Gos
Hauptdolomit
au
Hanauer Hütte
S
N
The presence of fault-related progressive unconformities shows that the Gosau
Group of Muttekopf was deposited in a zone affected by active folding and tearing.
N
Analogue model experiment of
growth structure (Ortner et al. 2015)
S
Reichspitze
Hau
ptd
Hauptdolomit
Uppe
r Gos
au
unconfo
r
a
rmity
Schlenkerk
olo
mit
Geometry of growth strata in a transpressive fold belt: Gosau Group at Muttekopf II.
During our fourth field day we could take a closer look on the stratigraphy of the
Santonian-Campanian part of the Upper Gosau Subgroup. The sedimentation started
with the deposition of dolo-conglomerates of alluvial fans, which is overlaid by shallow
marine Inoceramus marl. The cover turbiditic succession is built up by upward coarsening
sequences: first deep marine black shales, than turbiditic sandstone with Bauma series
were deposited. Upward, thick deep marine conglomerate intercalations are more and
more frequent. The overlying shales of the next sequence caused fluid overpressure in
the conglomerate body, which resulted the fluidisation and the chaotic mix of these
soft-sediments. In the turbitic sandstone trace fossils and spectacular soft-sediment
fold (slumps) occured.
W
E
rate
Hauptdolomit
er
wat
te
era
te
-wa
p
dee
itic
st
and
s
NW
Trace fossils
Soft-sediment fluidisation
m
glo
n
r co
id
turb
Slump fold in sandstone, which is covered by conclomerate.
g
con
p-
dee
one
SE
e
lom
Syn-sediment deformation on passive margins: Rofan Mountains
W
E
We finished our field trip in the Rofan mountains.
SHere
we had the chance to study the geometry of
the Rofan Breccia which was dragged along the
active normal fault (at left). We can interpret this
geometry as a clear evidence for the syn-tectonic
sedimentation of the breccia.
ia
an
Rof
cc
Bre
ia
Rofan Brecc
Neptunian dyke or olistolith (white limestone) in
the Lower Jurassic Red Limestone▼
ne
to
imes
tL
hä
berr
co
nt
a
ct
O
ne
to
imes
ät L
rrh
Obe
Reconstructed geometry of the syn-tectonic Upper Jurassic Rofen Breccia above the Upper Triassic Oberrhät Limestone ▲
Elsewhere we see thrusts and large scale folds which also
formed at the same time as the Rofan Breccia and the
extencional folds. How is that possible?
Rofan Breccia
Contemporanous breccia deposition, normal faulting,
thrusting and folding indicate large scale slumping. In the
Rofan mountains slumping is related to the Upper Jurassic Ruhpolding Radiolarite
Red Limestones
initiation of the thrusting at the seafloor previuosly formed
by extension (at right). The thrusting caused instability on
the slopes where slumping occured.
Oberrhät Limestone
Interpretation of the observed structures in the Rofan Mountains ►
Kössen Formation
Modified after
Brandner & Gruber 2011
Relationship of the Inntal and Lechtal thrust sheets
On the fifth day of the field trip, our team had the possibility to take a look at the
relationship of the major tectonic units of the Northern Calcareous Alps in the
Karwendel Mountains. During the ascent from the Eng valley, we could examine the
Inntal thrust from many different views. The interpreted field panorama photo shows
the northwards thrusting of the Early Mesozoic strata by the Late Cretaceous Inntal
thrust. The thrusting resulted in the formation of a kilometre-scale anticline building
up the Gamsjoch. Some minor out-of-sequence thrust faults occurred during the
folding. The Inntal thrust and its related fold is crosscut by a later (supposedly
Neogene) northwestward breakthrough-thrust. According to the classical
nomenclature of Tollmann (1976), the boundary between the Inntal thrust sheet and
the Lechtal thrust sheet is the breakthrough-thrust. However, both thrust sheets are
built up by the same succession, so their subdivision into two tectonic units is
questionable, and may reflect to the importance of considering the lateral variability
of even the most significant structures of an area.
SSW
Binasalm-Niederleger provided the accomodation
place on our last night on the field.
Inntal thrust sheet sensu stricto
Lechtal thrust sheet sensu stricto
Gamsjoch
Gumpenspitze
hrust
Inntal t
ug
ro
kth
a
bre
Various Lower Jurassic clastic sediments
Kössen Fm. (Upper Triassic)
Wetterstein Fm. (Middle Triassic)
Reifling Fm. (Middle Triassic)
Steinalm Fm. (Middle Triassic)
Virgloria Fm. (Middle Triassic)
Reichenhall Fm. (Lower to Middle Triassic)
t
us
hr
h-t
NNE
ALPS 2016
1-8 SEPTEMBER
93öu4
Acknowledgements
First of all, we are very greatful for the financial support of the Austrian Hungarian Action Foundation
(93öu4). Special thanks to our local host and leader, prof. Hugo Ortner. Without his help and
exceptionally interesting guidance, our field trip would not have been organized.
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