GeolCarp_Vol62_No3_279

www.geologicacarpathica.sk

GEOLOGICA CARPATHICA

, JUNE 2011, 62, 3, 279—295 doi: 10.2478/v10096-011-0022-y

Introduction

The study focuses upon the upper section of the Enns River,
which is one of the largest tributaries to the Danube in Aus-
tria and emphasizes the dominating forces that contributed to
the present-day diversity of morphology of the Upper Enns
Valley.

The dynamic evolution of a fault-controlled valley and its

drainage system cannot be seen as an isolated process but in
the context of the landscape involved. Surface uplift of moun-
tains,  rivers  and  drainage  patterns,  faults,  erosion  and  sedi-
mentation  as  well  as  climatic  impacts  are  reflected  by  the
landscape (Kuhlemann et al. 2001a). As a result of the colli-
sion  of  the  European  and  Adriatic  plates,  the  morphogenetic
evolution  of  the  Eastern  Alps  started  in  the  Oligocene  (from
ca. 30 Ma onwards; Frisch et al. 2000a). Approximately N—S
directed plate convergence caused thrusting and crustal thick-
ening  during  continental  collision  (Ratschbacher  et  al.  1989,
1991;  Peresson  &  Decker  1997a,b;  Neubauer  et  al.  2000;
TRANSALP  Working  Group  2002).  Crustal  thickening  and
isostatic uplift formed the first coherent relief (Hejl 1997). The
tectonic  evolution  was  driven  by  shortening  of  the  orogenic
wedge and by onset of the eastward oriented lateral extrusion
of  the  Central  Eastern  Alps.  An  important  feature  of  eastern
sectors of the Northern Calcareous Alps and central sectors
of the Eastern Alps is the Miocene Salzach-Enns-Mariazell-

Neotectonics, drainage pattern and geomorphology of the

orogen-parallel Upper Enns Valley (Eastern Alps)

MELANIE KEIL

and FRANZ NEUBAUER

Division of General Geology and Geodynamics, Department Geography and Geology, University of Salzburg, Hellbrunner Straße 34,

A-5020 Salzburg, Austria; Melanie.Keil2@sbg.ac.at; Franz.Neubauer@sbg.ac.at

(Manuscript received March 3, 2010; accepted in revised form October 13, 2010)

Abstract: The geomorphology and neotectonics of the Upper Enns Valley (Austria) in the Eastern Alps reveal the
formation of a fault-controlled orogen-parallel valley. In the study area, the Eastern Alps have been under surface uplift
since Early Miocene times. Quaternary processes such as uplift and cyclic glaciations likely interfere with neotectonic
activity as the Upper Enns Valley follows the Salzach-Enns-Mariazell-Puchberg (SEMP) fault. The geomorphologi-
cally different landscapes comprise three main tectonic units: (1) the Austroalpine crystalline basement exposed in the
Niedere Tauern, (2) the Austroalpine Paleozoic units (Greywacke Zone) and (3) the Dachstein Plateau dominated by
Triassic carbonate successions. The Upper Pleistocene Ramsau Conglomerate overlying the Greywacke Zone on the
northern slope of the Upper Enns Valley is a crucial element to reconstruct the evolution of the valley. A new

C date

(uncalibrated) indicates an age older than 53,300 years, outside of the analytical limit of the methods. Provenance
analysis of the Ramsau Conglomerate shows the Niedere Tauern as a source region and consequently a post-early Late
Pleistocene dissection of the landscape by the Upper Enns Valley. Paleosurfaces at elevations of about 1100 m on the
northern and southern slopes of the Upper Enns Valley allow us to estimate surface uplift/incision of about 2.5 mm/yr.
Regularly oriented outcrop-scale faults and joints of the Ramsau Conglomerate document Pleistocene to Holocene
tectonic deformation, which is consistent with ongoing seismicity. Paleostress tensors deduced from slickensides and
striae of pre-Cenozoic basement rocks indicate two stages of Late Cretaceous to Paleogene deformation independent of
the SEMP fault; the Oligocene—Neogene evolution comprises NW—SE strike-slip compression followed by E—W com-
pression and Late Pleistocene ca. E—W extension, the latter recorded in the Ramsau Conglomerate.

Key words: Quaternary, Eastern Alps, seismicity, tectonic deformation, paleostress analysis, provenance analysis,
Ramsau Conglomerate Formation.

Puchberg  (SEMP)  fault  striking  WSW—ENE  over  400 km
from the northern Tauern Window in the west to the Vienna
Basin in the east (e.g. Ratschbacher et al. 1991; Linzer et al.
1997). The SEMP-fault represents the northern margin of the
principal eastward extruding block. During Early and Middle
Miocene times, the Adriatic plate continued to move towards
the  stable  European  lithosphere  (Ratschbacher  et  al.  1989,
1991).  The  southern  sectors  of  the  Eastern  Alps  experienced
crustal shortening, and, in the northern sectors of the Eastern
Alps,  numerous,  mostly  orogen-parallel  sinistral  strike-slip
fault-systems were the consequence of indentation. N—S short-
ening changed from thrusting and crustal thickening to lateral
extrusion  and  orogen-parallel  extension  (Ratschbacher  et  al.
1989,  1991;  Peresson  &  Decker  1997a,b;  Frisch  et  al.  1998,
2000b;  Sachsenhofer  2001),  and  affected  and  formed  the  to-
pography  of  the  Eastern  Alps  in  Early  to  Middle  Miocene
times (Fig. 1a). Strong Neogene strike-slip tectonics were re-
sponsible for not only the eastward extrusion of the Austroal-
pine upper crust but also for the development of the west-east
trending fault-controlled Paleo-Enns Valley with tributary riv-
ers, the Paleo-Mur-Mürz (Dunkl et al. 2005) and locally fault-
controlled basins. Investigations in the westernmost Wagrain
sedimentary basin between Altenmarkt and Wagrain (Fig. 1b)
demonstrate  that  the  development  of  the  basin  is  concurrent
with the formation of the SEMP and Mandling faults in Early
Miocene times (Wang & Neubauer 1998; Neubauer 2007).

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Fig. 1. a – Simplified tectonic map of the Eastern Alps showing N—S shortening and lateral extrusion (modified after Keil & Neubauer
2009; credit to Österreichische Geologische Gesellschaft). b– Simplified geological map of the Upper Enns Valley region showing major
structural units.

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Some major extrusion-related fault zones are recognized to

be  still  active,  among  others,  the  SEMP  fault  (Reinecker  &
Lenhardt  1999;  Lenhardt  et  al.  2007);  shallow  low-magni-
tude  earthquakes  have  been  reported  from  the  study  area
(M 0.7—4.1).

We document, for the first time, deformation structures in

a Pleistocene conglomerate and use geomorphological fea-
tures to deduce steps of surface uplift of the region. We also
present a new

C-age of lignite from the Ramsau Conglom-

erate documenting an older age of this formation than previ-
ously suggested.

Materials and methods

Basic materials are the topographic maps ÖK 25V,

sheet 127 Schladming and sheet 128, Gröbming, Geologische
Karte  der  Republik  Österreich,  1 : 50,000,  sheet 127  Schlad-
ming  (Mandl  &  Matura  1995),  and  digital  elevation  models
(DEM). Fieldwork focused on the Ramsau Conglomerate, the
tributaries  of  the  Enns  River  and  the  Schladming  Basement
Complex  and  comprised  geomorphological  and  sedimento-
logical  investigations.  A  provenance  analysis  and  structural
analyses of the Ramsau Conglomerate were carried out in de-
tail.  The  approach  of  the  provenance  analysis  of  conglomer-
ates  followed  Ritts  et  al.  (2004)  and  Yue  et  al.  (2003).
Slickenside and striation data were collected along the tribu-
taries of the Enns River and at the bottom of the Schladming

Basement Complex. Paleostress orientation patterns of faults
and slickensides were evaluated by using the Tectonics FP
computer programme (Ortner et al. 2002).

Geological and geomorphological setting

The ENE-trending sinistral SEMP fault (Ratschbacher et al.

1991; Wang & Neubauer 1998) is supposed to run along the
Upper Enns Valley in the study area. The fault itself is largely
hidden  by  the  Holocene  valley  fill  (alluvial  deposits)  and  is
likely  located  along  the  southern  margin  of  the  valley.  The
Upper  Enns  Valley  separates  the  crystalline  basement  of  the
Schladming Tauern as part of the Niedere Tauern in the south
from the Greywacke Zone and the Northern Calcareous Alps
with  the  Dachstein  plateau  in  the  north  (Fig. 2).  In  addition,
the  ENE-trending  dextral  Mandling  fault  transects  the
Greywacke Zone, and the Mandling wedge, composed of Me-
sozoic rocks of the Northern Calcareous Alps, is exposed to its
south.  The  Mandling  wedge  is  interpreted  as  representing  a
strike-slip duplex of the Northern Calcareous Alps.

The southern and the northern slopes of the Upper Enns

Valley  differ  significantly  in  geomorphology  and  geology.
Three  geomorphologically  different  types  of  landscapes  are
characteristic for the main tectonic units, namely the Austroal-
pine  crystalline  basement  with  gneisses,  granites  and  mic-
aschists  represented  by  the  rugged  relief  in  the  Niedere
Tauern,  the  Austroalpine  Paleozoic  unit  (Greywacke  Zone)

Fig. 2. Digital elevation model of the study area indicating the geological and geomorphological setting. Numbers refer to locations of main tribu-
taries to the Enns River shown in Fig. 4: 1 – Grubbach, 2 – Grießenbach, 3 – Gradenbach, 4 – Aichbergbach, 5 – Eisbachgraben, 6 – Pre-
uneggbach, 7 – Talbach/Obertalbach, 8 – Dürrenbach, 9 – Gumpenbach, 10 – Seewigtalbach, 11 – Auerbergbach, 12 – Sattentalbach.

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with lithologies of high erosivity and the Permomesozoic cov-
er rocks dominated by Triassic carbonate sequences with steep
rock faces and the Oligocene/Early Miocene Dachstein pla-
teau on top.

Pronounced geomorphological differences can be observed

between the northern and southern valley flanks. The Ramsau
plateau (ca. 1100 m a.s.l.) is located ca. 340—360 m above the
present-day valley bottom; its southern boundary displays
sharp-edged scars (Fig. 2). Fine-grained sediments promote
water outlet, resulting in deeply carved channels. Alluvial fans
on the north side of the valley display scars ca. 20 m above the
present-day valley bottom.

The southern tributary valleys form larger alluvial fans than

those  from  the  northern  side  and  significant  canyons,  epige-
netic gorges and distinct knick zones. The valleys are narrow;
the  valley  slopes  are  steep  or  subvertical.  Mass  movements
and landslides, which developed on weak phyllite lithologies
of  the  Ennstal  Quartzphyllite  zone,  have  shaped  the  slopes
facing the valley.

Stratigraphic units

The Schladming Basement Complex (part of the Niedere

Tauern)  is  exposed  on  the  southern  side  of  the  Upper  Enns
Valley  (Fig. 1b).  This  complex  consists  of  a  polymetamor-
phic,  Variscan  and  Alpidic  basement  with  medium-  to  low-
grade  para-  and  orthometamorphic  rocks  (Mandl  &  Matura
1987).  Para-  and  orthogneiss,  migmatite-gneiss,  quartz-phyl-
lite,  sericite-quartzite,  greenschist,  and  amphibolite  are  the
most frequently occurring rocks in the Schladming Basement
Complex.  The  westernmost  part  belongs  to  the  Lower  Aus-
troalpine  units  of  the  Radstadt  Tauern  with  the  Permian  Al-
pine  Verrucano-type  Quartzphyllite  Group  and  the  Lower
Triassic Lantschfeld Quartzite at its stratigraphic base (Mandl
& Matura 1987). To the south of the Upper Enns Valley, the
Schladming  Basement  Complex  is  overlain  by  the  Wölz
Micaschist unit and the Ennstal Quartzphyllite or its western
extension,  the  Wagrain  Quartzphyllite.  The  Schladming
Basement  Complex  exhibits  a  young  morphology  with  steep

slopes, and reaches elevations up to 2800 m a.s.l. (Reinecker
2000; Frisch et al. 2000a).

North of the Upper Enns Valley, in the wider Schladming

area, the Pichl unit represents the southern, structural lower el-
ement  of  the  Greywacke  Zone  and  the  Glutserberg  unit  the
higher one, exposed farther north (Fig. 2). These are separated
by the Mandling wedge. The Pichl and Glutserberg units com-
prise  phyllites  rich  in  quartz  veins  and  lenses,  greenschist,
grey metasandstone, and rare calcite and dolomite marble in-
tercalations.  The  Mandling  wedge  comprises  rare  lenses  of
Lower  Triassic  Werfen  Quartzite  cut  at  the  base  by  faults,
mainly Middle Triassic Gutenstein Dolomite and Upper Trias-
sic Dachstein Limestone (Matura 1987). Greywacke Zone and
Mandling  wedge  are  at  relatively  low  elevations  reaching
maximum altitudes of 1760 m.

The Glutserberg unit is overlain by the Permian to Upper

Jurassic  succession  of  the  Dachstein  block,  which  is  part  of
the Northern Calcareous Alps. The succession includes Perm-
ian  to  Lower  Triassic  siliciclastic  formations  (Alpine  Verru-
cano  and  Werfen  Formations).  These  lithologies  display  a
similar geomorphological expression to the Greywacke Zone.
A thick Middle to Upper Triassic dolomite and limestone se-
quence  including  the  Upper  Triassic  Dachstein  Limestone
forms  impressive,  steep  rock  faces.  Jurassic  formations  are
rare. The Dachstein Limestone forms a plateau at elevations of
ca. 2200—2400 m and peaks up to 3000 m a.s.l. Miocene clas-
tic  rocks,  the  so-called  Augenstein  Formation  comprising
mainly  well  rounded  vein-derived  quartz  pebbles  have  been
found  on  the  plateau  and  in  karst  holes  (Frisch  et  al.  2002;
Seebacher  2006,  e.g.  Dachstein  south  face  at  1770 m  a.s.l.).
This  proves  that  the  Dachstein  plateau  is  a  karstified,  Lower
Miocene paleosurface covered by fluvial deposits, now uplift-
ed to its present elevation (Frisch et al. 2001).

The Upper Pleistocene Ramsau Conglomerate overlies the

Pichl unit of the Greywacke Zone and forms much of the land-
scape of the northern slope of the Upper Enns Valley between
Pichl and Weißenbach/Haus (Fig. 3). Here, we introduce the
informal term Ramsau Conglomerate Formation for this sec-
tion. The base of the Ramsau Conglomerate Formation is at an
elevation of ca. 820 m in the west (Pichl) and ca. 780 m in the

Fig. 3. Simplified geological map of the study area (with main emphasis on the Pleistocene Ramsau Conglomerate Formation) between
N 47°23.652/E 013°36.506 and N 47°24.806/E 013°44.917. The E—W distance is about 12 km (modified after Mandl & Matura 1995). A—K – out-
crops for provenance analysis, L – location of Fig. 12, SEMP – Salzach-Enns-Mariazell-Puchberg fault.

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east (Birnberg road near Oberhaus railway station), and its top
forms an impressive planation surface, the Ramsau plateau at
an elevation of ca. 1100 m a.s.l. The conglomerate comprises
mainly a polymict conglomerate dominated by metamorphic
pebbles, rare sandstones and a widespread subhorizontal coal/
lignite seam at an elevation of ca. 965 m (Fig. 3). The coal ap-
pears dark brown, shrunk and shows the megascopic charac-
teristics of lignite (Weber & Weiss 1983; Sachsenhofer 1988).
It was subject to underground exploitation until 1947 (Weber
& Weiss 1983; Weiss 2007). The uncalibrated

C age is

31 ± 1.2 ka (van Husen 1987). The age of this lignite seam is
still uncertain in spite of spore/pollen analyses (Draxler 1977;
Draxler & van Husen 1978). The

C age is at the limit of the

method. Earlier opinions argue for an age of deposition in the
Riss/Würm Interglacial (e.g. Sachsenhofer 1988). The Ram-
sau Conglomerate Formation is covered by Upper Pleistocene
moraines and Holocene rivulets are incised into it.

Results

Drainage pattern

Though the fluvial channel of the Enns River represents

only a small proportion of the landscape in the study area, to-
gether with its tributaries from N and S, it may be the key to
explaining external and tectonic geological processes, which
resulted in formation of the present-day morphology. All trib-

utaries  are  oriented  aproximately  perpendicular  to  the  Upper
Enns  Valley.  The  Enns  River  flows  near  the  southern  valley
side, except where large alluvial fans coming from the south-
ern  tributaries  force  a  distal  flow.  The  longitudinal  valley  of
the Enns River has one characteristic feature, namely an asym-
metric drainage pattern of tributary rivers (Zötl 1960; Keil &
Neubauer 2009). Less than 15 percent of the drainage area is
located  north  of  the  Enns  Valley.  Tectonically  undisturbed
rivers  have  a  concave  longitudinal  profile,  steeper  near  the
source, shallow at lower reaches of the rivers. The gradients of
the  tributaries  to  the  Enns  River  are  not  smooth  at  all;  steep
reaches  change  with  sections  of  gentle  gradients  with  pro-
nounced  knick  points  in  between  (Fig. 4).  The  profiles  of
twelve tributaries show clear variations of the river gradients,
sometimes within rather short distances. To calculate the river
gradients we used the method of Burbank & Anderson (2001):
elevation change/length of the reach. The northern tributaries
of  the  Enns  River  represent  short  valleys  (2—5.5 km)  com-
pared  to  those  from  the  south,  which  are  up  to  15.5 km  in
length. Significant for the majority of the tributaries from the
north is the low gradient over a long distance before their con-
fluence with the Enns River (Fig. 4a).

The tributaries from the south caused accumulation of

comparably large alluvial fans on which most major villages
are located (Fig. 2). Each tributary shows profiles with sev-
eral  knick  points  followed  by  steep  sections.  These  steep
reaches  often  include  waterfalls  (e.g.  Gradenbach,  Seewig-
talbach)  and  canyons  (Talbach,  Dürrenbach)  in  crystalline

Fig. 4. Longitudinal profiles: a – Enns River, tributaries from north, b – Enns River,
tributaries from south. For locations, see Fig. 2.

Fig. 5. Longitudinal valley profile Preuneggbach—Grießenbach; these brooks are tributaries
from opposite sides of the Upper Enns Valley.

bed rocks, whereas the infill of flat
parts includes characteristic lake sedi-
ments and high moors.

Flat reaches over long distances are an

outstanding  feature  of  the  rivers,  the
sources of which lie at or above 1700 m,
for  example,  the  Preuneggbach  (length
of flat reach 6400 m), Talbach/Obertal-
bach (length of flat reach 4000 m), Sat-
tentalbach (length of flat reach 7600 m).
The flat reaches are located at elevations
between  1000 m  and  1100 m  (river
nos. 6,  7,  10,  11  in  Figure 4b)  and  be-
tween 800 m and 900 m (river nos. 6, 7,
10  in  Figure 4b).  These  flat  reaches  are
used  to  analyse  any  coincidences  be-
tween the northern and the southern side
of the valley and to reconstruct a possi-
ble Pleistocene valley bottom (Fig. 5).

Ramsau Conglomerate Formation:
provenance analysis

Descriptions dealing with the con-

glomerate north of the Upper Enns Val-
ley  are  rare  (Spaun  1964;  van  Husen
1981, 1987). Today, the stratigraphic se-
quences  of  the  Ramsau  Conglomerate
Formation are well exposed from 760 m
to ca. 1100 m a.s.l. north of Schladming.
The  same  lithostratigraphic  succession

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has been observed on the southern slope of Mit-
terberg, about 10 km farther east (Fig. 1b).

The bedding of the whole section is subhori-

zontal and the entire section is about 340 m
thick (Fig. 6).

The section comprises from base to top: (1)

Thick-bedded  coarse-grained  (2—5 cm)  massive
conglomerates (ca. 10 m in height) representing
deposits of alluvial fans, which are now dissect-
ed  by  small  facets;  (2)  a  sharp  edge  forms  the
boundary  to  massive  conglomerates,  –  ca.
20 m  in  height  –  with  easily  accessible  out-
crops  of  the  Ramsau  Conglomerate  Formation;
(3)  above,  conglomerates  with  mostly  well-
rounded clasts intersected by meter-scaled sand-
stone layers grade at an elevation of 900 m, into
(4) a succession of siltstone and mudstone con-
taining  (5)  a  lignite  seam  at  an  elevation  of
965 m.  Above,  (6)  a  coarse-grained,  polymict
conglomerate is arranged in 10 m thick beds, the
uppermost  layers  are  poorly  sorted.  A  ground
moraine  covers  the  Ramsau  Conglomerate  For-
mation.

We interpret the conglomerate beds as alluvial

fans, according to criteria summarized in
Schäfer (2005). On the whole, the lower part of
the succession represents a fining upward cycle
up to the lignite level. The middle stratigraphic
levels with mudstone and lignite are interpreted as
lake sediments, already proposed by van Husen

(1981) and Draxler (1977). A coarsening upward cycle rep-
resents the higher stratigraphic level.

The clast compositions of eleven stations between 768 and

1081 m  a.s.l.  were  determined  by  counting  approximately
100  clasts  per  exposure  on  regularly  spaced  grids,  ca.
20 20 cm.  Only  clasts  with  a  minimum  grain  size  of  1 cm
were  counted  because  of  easy  identification.  Results  are
shown in Figure 7. Clasts originate from: (1) AA crystalline
basement  (Ennstal  Quartzphyllite,  paragneiss,  orthogneiss,
amphibolite, vein quartz); (2) AA metamorphic cover ( green
quartzite,  green  quartzitic  phyllite,  light  quartzite,  calcitic
marble);  (3)  GWZ  (Alpine  Verrucano-type  quartz-phyllite,
vein-derived  quartz  pebbles,  dark  quartzite,  green  quartzite,
phyllite,  Ennstal  Quartzphyllite);  (4)  NCA  (Hallstatt-type
limestones,  Gutenstein  Limestone,  red  calcitic  sandstone  as
well  as  dark  and  light-coloured  sandstone  from  the  Werfen
Formation at the base of the Northern Calcareous Alps. Hall-
statt  type  limestones  are  abundant  in  the  NW  of  the  study
area, e.g. Scheidleder et al. (2001). There are three groups of
clasts: (1) clasts, formed within greenschist-facies metamor-
phic  conditions,  (2)  clasts  of  a  higher  metamorphic  grade
like amphibolite, para- and orthogneiss as well as marble and
quartz-bearing  marble  (derived  from  the  Schladming  and
Wölz  Basement  Complex),  and  (3)  limestones  and  sand-
stones derived from the Northern Calcareous Alps.

Fig. 6. Stratigraphic sequences of the Ramsau Conglomerate For-
mation (^^ facets); numbers 1—6 relate to description in the text.

Fig. 7. a – Provenance analysis of the Ramsau Conglomerate Formation at dif-
ferent elevations; A—K refer to sites in Fig. 3; b – summarized result of the
provenance analysis.

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C dating of lignite

To assess the previously published age of the lignite from

the Ramsau Conglomerate Formation (Draxler & van Husen
1978) we collected a new lignite sample at 965 m a.s.l. by
excavation. The sample coordinates are N 47°23

’49.403”,

E 13°38

’42.433”. The

C analysis was performed by accel-

erator mass spectrometry at the VERA facility of the Universi-
ty of Vienna (VERA-5152, sample Ramsau 1). The analytical
data are given in Table 1 (Appendix). The

C abundance is

below the detection limit representing a

C-age older than

53,300 years.

Glacial overdeepening of the Upper Enns Valley

The Upper Enns Valley is filled with Holocene gravels,

and the overdeepening of the valley is explained by glacial
carving (Spaun 1964; van Husen 1987; Becker 1987; Reitner
& van Husen 2007).

The ablation area of the Würm glaciations formed large

overdeepened parts of the valley (van Husen 2000). Drillings
and results of geophysical surveys (Becker 1981, 1987) give
improved information about sediment thickness and the po-
sition  of  the  underlying  bedrock  in  the  Upper  Enns  Valley
(Fig. 8).  It  shows  that  glacial  overdeepening  between  Man-
dling and Wörschach is of greater extent than originally as-
sumed  (Becker  1981,  1987).  At  Mandling,  the  valley  fill  is
about 150 m, the bedrock lies at 650 m a.s.l. The Quaternary
fill  of  120—130 m  suggests  the  bedrock  at  Schladming  at

595 m a.s.l. which results in a rather constant river gradient of
about 0.5 % (Frisch et al. 2000). Recent seismic profiling in
the eastern Enns Valley (between Liezen and Weng) shows
ca. 480 m of Quaternary sediments (Schmid et al. 2005).

Paleostress in the basement

Geological considerations and large-scale offsets indicate a

sinistral transtensional motion with the northern block moving
down  along  the  SEMP  (Genser  &  Neubauer  1989;  Ratsch-
bacher et al. 1991; Wang & Neubauer 1998; Keil & Neubauer
2009). Detailed fault-slip data and their paleostress assessment
from the SEMP fault were mainly published from a segment
north  of  the  Tauern  Window  (Wang  &  Neubauer  1998)  and
from the easternmost sectors of the Northern Calcareous Alps
(Nemes  et  al.  1995).  From  the  Upper  Enns  Valley,  no  data
were published and our aim is to fill this gap.

A list of investigated stations together with geographical sit-

uations and lithological descriptions is given in Table 2 (Ap-
pendix). The sense of slip was deduced from offset markers,
Riedel  shears,  the  surface  morphology  of  slickensides  and
quartz fibers. The raw data contain partly fault-slip sets with
incompatible  slip-sense;  the  Tectonics  FP  computer  program
was used to sort the data and to calculate paleostress tensors
(Ortner et al. 2002). Only results from those sites are reported
where  measurements  are  related  to  a  significant  (four  and
more) number of fault-striae pairs after separation of data.

The number of overprint criteria is limited. However, a de-

tailed analysis allows us to infer a specific succession of brittle

Fig. 8. Geographical setting of locations indicated in a sketch of glacial overdeepening in the Upper Enns Valley from Mandling to Hieflau
(modified after Becker 1987 & van Husen 1987; sources of drill hole data STEWEAG 1978).

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Fig. 9. a – Localities of paleostress tensor groups A and B, b – Localities of paleostress tensor groups C and D.

tectonic events (see below). The same is valid for the timing
as  no  Cenozoic  sediments  are  exposed  in  the  working  area,
which would allow us to construct a paleostress stratigraphy.
For  that  purpose,  we  follow  the  analyses  of  Peresson  &
Decker  (1997a,b)  from  the  adjacent  Northern  Calcareous
Alps and of Wang & Neubauer (1998) from the SEMP fault
west  of  the  study  area.  The  timing  given  in  these  studies  is
based on interferences with the Miocene sedimentary depos-
its and Oligocene metamorphism in the Tauern Window.

Figures 9 and 10 show the results of the paleostress analy-

sis. We found four distinct paleostress tensor groups labelled
A to D.

Paleostress tensor group A defines an event with N—S

compression and mainly strike-slip faults. NW-trending dex-
tral and NNE- to NE-trending sinistral strike-slip faults dom-
inate. S-dipping thrust faults are subordinate. Chlorite and
quartz fibers on fault surfaces indicate motion under hydro-
thermal conditions. Consequently, rocks were at 3—6 km
depth beneath the surface during fault motion. The suggested
formation time is Late Cretaceous to Paleogene (see Discus-
sion section).

Paleostress tensor group B comprises E/SE and W/NW-

dipping normal faults indicating E—W extension which over-

prints the former N—S compressional structures (e.g. outcrop
no. 15 in Figure 9). This set is also characterized by chlorite-
and quartz fibers, again indicating formation under hydrother-
mal conditions. Furthermore, in two cases, we found N—S
extension (labelled paleostress tensor group B

) on mostly

S-dipping normal faults. No overprint criteria were found for
this group. The limited number of group B

leaves it uninter-

pretable.

Paleostress tensor group C comprises ca. N—S trending

sinistral strike-slip faults and ca. E—W trending, steeply S-dip-
ping dextral strike-slip faults. Together, these faults indicate
ca. NW—SE compression, also indicating a dextral shear along
the ENE-trending SEMP fault. Wang & Neubauer (1998) as-
sume a pre-Early Miocene age for this group of faults because
it is not recorded in the Miocene Wagrain Basin. Overprints
on the older fault sets were observed at localities 3, 6 and 10
(Fig. 9).

Paleostress tensor group D comprises ca. ENE-trending

dextral and NW to NNW-trending sinistral strike-slip faults
together constituting ca. E—W compression. Peresson &
Decker (1997a,b) assume a Pliocene age for this group.

Interestingly, virtually no record of sinistral shear along

the SEMP fault was found.

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Ramsau Conglomerate Formation: deformation structures

Shallow dip of bedding (2—10°) is found in the Ramsau

Conglomerate Formation near the edge of the Ramsau plateau
(Fig. 11). Bedding planes with dip angles  > 30° are developed
at  lower  elevations  and  farther  east  close  to  the  base  of  the
Ramsau  Conglomerate  Formation,  near  Birnberg  where  nor-
mal  faults  are  exposed.  The  moderately  W-dipping  bedding

planes are associated with listric normal faults; they represent,
therefore, rollover-type structures.

In many outcrops joints are steep to subvertical and show

three trends: a) ENE, b) NE and c) N. The first two sets can be
interpreted  as  conjugate  Mohr  fractures  (Fig. 11b,  sets  a, b)
and  the  N—S  trending  joints  as  extensional  structures
(Fig. 11b,  set  c).  The  conjugate  Mohr  fractures  indicate  ca.
NE—SW  contraction  (as  shown  in  Fig. 11b),  the  N-trending
joints E-extension, roughly consistent with normal faults.

Normal faults in several outcrops coincide in orientation

with NNE-dipping joints (Fig. 11c). Particular impressive ex-
amples of nearly vertical faults can be found on the road
Schladming—Ramsau Leiten (Fig. 12, location L in Figure 3).

The dip of faults is perpendicular to valley slopes exclud-

ing  an  origin  as  mass  movement;  they  dip  steeply,  or  with
medium  angle,  to  the  ESE.  Primarily,  these  faults  indicate
WNW—ESE  to  E—W  extension.  We  observed  regularly  ori-
entated offsets of ca. 1.0 to 1.2 m.

A lignite seam is intercalated in the Ramsau Conglomerate

Formation at middle stratigraphic levels. The lignite seam is
flat-lying and can be traced in a W—E direction for about six
kilometers (Weiss 2007). The original underground-mining
map indicates several faults (“Sprung”). Two orientations are

Fig. 10. Fault and striae data and their paleostress assessment from basement rocks along the SEMP and Mandling faults. Numbers accord-
ing to localities in Fig. 9 and Table 2; lower hemisphere equal-area projections.

Fig. 11. Ramsau Conglomerate Formation: (a) orientation of bed-
ding planes, (b) joints and (c) faults; lower hemisphere equal-area
projection.

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Fig. 12.  Field
p h o t o g r a p h
and  a  parallel
scheme  show-
ing an array of
steep  normal
faults  within
the

Ramsau

Conglomerate
Formation, NE
Schladming.

Fig. 13. Photolineaments in digital ele-
vations models of (a) the Ramsau pla-
teau area and (b) Mitterberg.

reported  in  the  map:  ca.  E-trending  faults  with  the  northern
block  down,  and  ca.  NNE-trending  faults  with  the  eastern
block down. Weber & Weiss (1983) report vertical offsets of
ca. 2.5 meters at maximum. The NNE-trending normal faults
are  subparallel  to  normal  faults  of  surface  exposures  within
the Ramsau Conglomerate Formation.

Photolineaments have been studied from the Ramsau pla-

teau and Mitterberg using digital elevation models (Fig. 13).

The  Ramsau  plateau  displays  several  ca.  E-  and  subordinate
NNE-trending  lineaments,  which  can  be  traced  ca.  1.5  to
3 km. Some N- to NNW-trending lineaments are much short-
er. The E-trending lineaments of the Ramsau plateau are simi-
lar in orientation to the E-trending normal fault of the lignite
seam and suggest N—S extension. The N-trending lineaments
correspond  to  the  N-trending  measured  surface  structures  of
the Ramsau Conglomerate Formation.

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ENE-trending lineaments occur on Mitterberg (Fig. 13b).

A further, prominent NW-trending lineament cuts the Mitter-
berg  block  in  the  west;  geomorphic  evidence  argues  for  a
dextral  displacement  (Fig. 13b,  point 1;  Table 2,  site 17).  A
NNW-dipping  normal  fault  within  the  Ramsau  Conglomer-
ate Formation was observed at location 2 (Fig. 13b).

In summary, trends of surface joints and faults conform in

their orientation and prove similar kinematics as subsurface
faults  and  photolineaments:  (1)  ca.  N—S  extension,  (2)  ca.
ESE—WNW  to  E—W  extension,  and  (3)  NE—SW  compres-
sion,  which  is  recorded  only  in  conjugate  Mohr  fractures.
The  development  of  the  latter  two  could  be  related  to  the
same stress field.

Recent seismicity

The Upper Enns Valley is not indicated as an area of in-

tense  seismicity,  but  within  the  polygon  grid  Ennstal  111
seismic  events  have  been  recorded  between  1987  and  2005
(Rieder,  pers.  comm.  2005);  magnitudes  were  between  0.7
and 4.1. These earthquakes were rather shallow; hypocenters
are  located  at  a  depth  between  6  and  8 km  (Lenhardt  et  al.

2007). However, as if to underline our work, an earthquake
occurred in the study area on July 19

, 2008 with a magni-

tude of 3.8 and an epicentral intensity of 5 EMS (European
Macroseismic Scale).

Fault plane solutions are only available from adjacent re-

gions  (Fig. 14,  NNE  of  Salzburg).  The  orientation  of  maxi-
mum  compression  trends  either  NE—SW  or  NNE—SSW
(Reinecker  &  Lenhardt  1999;  Lenhardt  et  al.  2007)  corre-
sponding to paleostress orientations deduced from fault ori-
entations  within  the  Ramsau  Conglomerate  Formation  (see
above).

Discussion

In the following, we discuss the different aspects that con-

tributed to the evolution of the Upper Enns Valley. First, we
discuss  the  paleostress  evolution  of  the  SEMP  fault  in  the
context of the evolution of the Upper Enns Valley, the devel-
opment of the drainage pattern, then Quaternary events as re-
corded  by  the  Ramsau  Conglomerate  Formation,  surface
uplift/incision  rates,  glacial  overdeepening  and  recent  seis-

Fig. 14. Stress S

orientations of the eastern sectors of the Eastern Alps (modified after Reinecker & Lenhardt 1999).

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micity. A further description and discussion of vertical mo-
tion north and south of the SEMP fault/Upper Enns Valley
can be found in Keil & Neubauer (2009).

Kinematics and paleostress evolution

Paleostress tensor orientations of slickensides and striae

along  the  tributaries  of  the  Enns  River  and  apart  from  the
Ramsau Conglomerate Formation record four different stress
groups  compared  to  the  six  stress  groups  of  Peresson  &
Decker  (1997)  east  of  our  working  area  along  the  SEMP
fault. We show below that our data are in part significantly
different from those of Peresson & Decker (1997). A partly
similar  succession  of  deformation  events  has  been  found
within and around the Wagrain Basin (Neubauer 2007) and
along  the  SEMP  fault  at  the  northern  margin  of  the  Tauern
Window.

Paleostress tensor group A indicates N—S strike-slip

compression.  The  event  displays  abundant  evidence  for  hy-
drothermal  activity  resulting  in  quartz  and  chlorite  fiber
growth. Similar events are recorded for deformation related
to ductile to brittle low angle normal faults formed in T-con-
ditions of ca. 200—300 °C, leading to the subsidence of Up-
per Cretaceous to Paleogene Gosau basins (e.g. Neubauer et
al. 1995; Koroknai et al. 1999). However, Peresson & Decker
(1997a)  assume  a  Late  Eocene  to  questionable  Oligocene
age in the Northern Calcareous Alps.

Group B is concentrated in the western section of the

Enns  Valley.  High-angle  normal  faults  with  quartz-  and
chlorite fibers indicate ca. E—W extension, a widespread ori-
entation in Austroalpine units, and possibly suggest the wan-
ing stage of the Gosau E—W extension event (e.g. Neubauer
et  al.  1995;  Koroknai  et  al.  1999).  In  accordance  with  their
data,  we  assume  therefore,  a  Late  Cretaceous  to  Paleogene
age  for  paleostress  tensor  groups  A  and  B.  The  timing  of
groups A and B is different to that from Peresson & Decker
(1997a), and does not go conform to the topic of the paper.

Group C (NW—SE compression) occurs along the total

length of the study area (12 km) only north of the SEMP
fault. We suggest that group C already indicates the onset of
reactivation along the sinistral SEMP fault, as at locations 3,
6, 10 in Figure 9.

Group D recording ca. E—W strike-slip compression in-

dicates  the  end  of  the  lateral  tectonic  extrusion  event  and
suggests reactivation by dextral inversion of the initially sin-
istral  SEMP.  A  similar  reactivation  has  been  described  by
Peresson  &  Decker  (1997a,b)  for  the  eastern  part  of  the
SEMP fault and by Hinsch et al. (2005) for the Vienna Ba-
sin. These authors assume a Pliocene age for this stage. E—W
compression again only affects the northern side of the Up-
per Enns Valley.

The most interesting result is that hardly any evidence

for sinistral strike-slip and oblique-slip motion along steeply
NNW-dipping faults has been found in the working area as
could have been expected from the sinistral nature of the
SEMP fault as revealed by geological reasons.

A further result is that deformation is not reflected in brit-

tle structures in basement rocks except the scarce evidence
for N—S extension in paleostress tensor group B

Evolution of drainage pattern

The drainage pattern of the Eastern Alps largely reflects

extrusion  tectonics  (Frisch  et  al.  2000a;  Robl  et  al.  2008b)
and  major  rivers  like  the  Enns  River  follow  major  faults  of
the extrusional wedge. The formation of the drainage system
is  connected  with  fault  activity.  Robl  et  al.  (2008a)  assume
that the elbow-shaped bend of the Enns River near Hieflau is
a  consequence  of  displacement  along  the  SEMP.  A  similar
phenomenon characterizes the Enns River SE of Mitterberg,
where it turns from E to N. However, the impact of glacia-
tions may be responsible for the reorganization of the drain-
age system, as well.

The steep slopes on the southern side of the Enns River

can  be  seen  as  a  result  of  neotectonics,  and/or  of  glacial
overdeepening (Székely et al. 2002). Erosion in the tributary
courses  is  enhanced  by  the  high  gradients  and  lithological
erodability.  Erosion  that  deepens  the  river  valleys  but  does
not  erode  peaks  reduces  the  mass  of  an  area  and  leads  to
peak  uplift  as  a  consequence  of  isostatic  adjustment  (Bur-
bank  &  Anderson  2001).  Such  a  process  by  glacial  over-
deepening  and  widening  of  valleys  was  considered  to  be
responsible for Quaternary surface uplift by Pelletier (2008).
The  high  rate  of  stream  incision  below  the  paleosurfaces
south of the Enns River could be considered as proportional
to shear stress exerted by turbulent flowing conditions of the
tributaries (Schlunegger et al. 2001). This possibly explains
the profile geometry in a tectonically active area. Surface up-
lift and incision rates are higher south of the Enns River than
north of it. The tributaries from the north show a significant-
ly low stream gradient over long distances. A series of trian-
gular facets borders the abrupt transition to a lower gradient;
these facets in connection with the low stream gradient and
the distally flowing Enns River could be the result of a slow-
er surface uplift rate at the northern side of the valley. Obvi-
ously,  tectonic  and  morphological  perturbations  are  more
effective in the southern part of the Upper Enns Valley. Con-
sequently, this leads to the assumption that the SEMP strike-
slip fault primarily affects the southern side of the valley.

Relating to Becker (1981, 1987) that the Upper Enns Valley

was  filled  up  to  ca.  1050 m  during  the  Riss/Würm  Intergla-
cial,  the  correlation  of  the  paleosurfaces  at  ca.  1000—1100 m
and  800—900 m  on  both  sides  of  the  Enns  Valley  during  the
Quaternary suggests interglacial valley bottoms. Thus, the riv-
er  profiles  may  be  used  to  document  surface  uplift/incision
since the last glaciation (Fig. 5).

Glacial overdeepening

The present-day U-shaped Enns Valley profile is ex-

plained  by  glacial  overdeepening.  However,  the  overdeep-
ened  longitudinal  orogen-parallel  Upper  Enns  Valley
follows  the  tectonic  structure  of  the  SEMP  fault.  Tectonic
subsidence can be a reason for overdeepening in addition to
the  formation  by  glacial  erosion  (Reitner  &  van  Husen
2007). The thickness of Alpine valley infill and the depth of
the  underlying  bedrock  is  being  discussed  (Brocard  et  al.
2003).  The  filling  actually  depends  on  the  relation  of  the
main river to its tributaries; the Enns Valley glacier was re-

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sponsible for a base level lowering of 100—200 m (Robl et al.
2008a). Glacial valley overdeepening caused elevated stream
power  in  the  southern  tributaries  and,  consequently  led  to
steepening  of  the  slopes  in  the  Ennstal  Quartzphyllite  areas
south of the Enns River. The base of the Ramsau Conglom-
erate  Formation  at  820—780 m  a.s.l.  can  also  be  interpreted
as a previous stage of glacial overdeepening during the Riss
glaciation. After deglaciation, deposits filled the valley up to
ca. 1100 m a.s.l. and formed the base for re-incision.

Origin of the Ramsau Conglomerate Formation

The composition of the Ramsau Conglomerate Formation

demonstrates the great variety of the drainage area of the Up-
per  Enns  Valley;  an  exact  inventory  directly  refers  to  the
source  of  material,  as  the  different  components  of  the  con-
glomerate  are  mostly  rock  fragments  (Füchtbauer  1988).
Analysis of components from the Ramsau Conglomerate For-
mation  results  in  a  predominant  percentage  of  crystalline
clasts  at  all  stratigraphic  levels  (Fig. 7).  Even  90 km  farther
east  petrographic  studies  show  clasts  from  the  Upper  Enns
Valley with prevailing crystalline origin (Spaun 1964) imply-
ing a source from southern tributaries of the Enns River. The
specific  composition  of  clasts  (61 %  crystalline  rocks)  sug-
gests  primarily  the  provenance  from  the  medium  and  low-
grade  metamorphic  gneissic  terrain  of  the  Niedere  Tauern,
though transport-resistant components (quartzite, gneiss) pre-
vail  in  all  exposures;  material  from  the  Northern  Calcareous
Alps  is  subordinate  (24 %  unmetamorphic  carbonates,  15 %
sandstone).

Quaternary surface uplift

Several processes induce surface uplift. Erosional denuda-

tion  results  in  rather  low  uplift  rates  of  less  than  1  mm/yr
(Ruess & Höggerl 2002). Higher uplift rates can be reached
by  plate  motion  when  shortening  is  converted  into  crustal
thickening and therefore into isostatic uplift. In this case, the
uplift is also lower than horizontal plate motion. Finally, gla-
cial  unloading  can  also  result  in  surface  uplift  in  order  of
mm/yr in time scales of ca. 10 kyr. In the following, we try
to quantify uplift, or river incision for the Upper Enns Valley.

The age of the Ramsau Conglomerate Formation is still

uncertain; the embedded lignite seam at an altitude of about
965 m could be a clue for dating the conglomerate. The age
of the lignite seam has been dated to 30,700 yr ± 1200 yr by
the

C method (van Husen 1987). The valley floor of the

Upper Enns Valley is located at 738 m a.s.l.; the highest out-
crops of the conglomerate are around 1100 m a.s.l. The dif-
ference  in  elevation  leads  to  the  conclusion  of  an  uplift,  or
Enns River incision of ca. 360 m. If we assume that there has
been  an  uplift  of  about  360 m  during  the  last  30 kyr,  then
this dating results in an unrealistic uplif/incision of 12 mm/yr.
The main driving forces of uplift/incision include erosional,
glacial  or  deep-lithospheric  unloading,  plate  motion  or  a
mixture  of  all  these  processes  (Székely  et  al.  2002).  The
Adriatic  microplate  moves  northward  at  about  2.5 mm/yr
(D’Agostino  et  al.  2005;  Grenerczy  et  al.  2005).  If  we  as-
sume the plate motion as the main driving force, the uplift/

incision  rate  has  a  maximum  2.5 mm/yr,  in  spite  of  the
present  low  convergence  rate.  If  we  take  into  account  that
deposition of the lignite seam occurred already at the begin-
ning  of  the  last  Interglacial  at  about  120 ka  BP  as  our  new

C-date allows us to assume, then the surface uplift could be

explained by tectonic uplift with a minor component of post-
glacial unloading (Székely et al. 2002). The average vertical
difference  between  the  valley  bottom  and  the  Ramsau  pla-
teau  is  ca.  300 m;  thus,  the  result  seems  very  reasonable
(300 m/120,000 yr = 2.5 mm/yr). The new minimum value of
the lignite indicates an age of  > 53.3 ka and strengthens our
hypothesis.

Estimate of surface uplift

Paleosurfaces have been identified in several mountain

ranges (Burbank & Anderson 2001). Because the paleosurfac-
es  were  estimated  to  be  about  120 ka  old,  subtraction  of  the
present topography from this date might define the mean inci-
sion value. We observed that the generally steeper slopes be-
tween the flat reaches and the valley bottom on the southern
side of the Upper Enns Valley promote high erosion rates. The
S—N longitudinal profiles to the Enns Valley bottom indicate
an average uplift rate of 2.4 mm/yr and an incision up to ca.
300 m (Fig. 5). Generally, valleys following a fault zone show
enhanced incision rates (Robl et al. 2008a). The average uplift
rate of the paleosurfaces differs widely from the average sur-
face  uplift  of  the  Niedere  Tauern  ( > 1 mm/yr  relative  to  the
Bohemian  Massif  according  to  Ruess  &  Höggerl  2002).  Pa-
leosurfaces south of the Upper Enns Valley partly display dif-
ferent  elevations  and  do  not  match  exactly  with  the  Ramsau
plateau.  In  our  opinion  the  presence  of  terraces,  or  paleosur-
faces at different elevations indicate differential uplift on both
sides of the Upper Enns Valley. On the one hand, different up-
lift rates are due to lithological differences between the N and
S of the valley, and on the other hand due to the isostatic re-
bound of the deglaciation (Székely et al. 2002).

Quaternary deformation

The NNE-trending normal faults observed in the former

coal mine conform in orientation to joints and faults within the
Ramsau Conglomerate Formation and indicate a WNW—ESE
orientation  of  the  minimal  horizontal  stress  that  suggests
WNW—ESE  extension.  WNW—ESE  extension  may  be  corre-
lated with the overall extension during the Miocene lateral ex-
trusion  process  (Frisch  et  al.  2001).  The  lignite  seam  shows
offsets  up  to  2.5 m,  certainly  formed  later  than  the  lignite
(Weber  &  Weiss  1983).  The  high-angle  normal  faults  give
proof of recent neotectonic activity and are the consequence of
ongoing uplift of the Northern Calcareous Alps and lateral ex-
trusion. The lignite seam is likely to have formed during the
warm  period  of  the  last  Pleistocene  Interglacial  (Draxler
1977). The documented normal faults therefore record a post-
Eem  Interglacial  deformation.  A  normal  fault  in  the  western
part  of  the  underground  mine  records  ca.  NNW—SSE  exten-
sion and this event is consistent with the paleostress tensor of
the  so  far  uninterpretable  group  B

. The WNW—ESE exten-

sion of the second fault is consistent with surface observa-

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tions and with fault plane solutions of ongoing seismicity
(Reinecker & Lenhardt 1999).

WNW—ESE extension in most exposures resulted in tilt-

ing  of  some  portions  of  the  Ramsau  Conglomerate  Forma-
tion.  The  minimum  horizontal  stress  is  assumed  to  have  a
uniform WNW to ESE orientation. This orientation of recent
stress has already been observed within the highest tectonic
stratigraphic  units,  such  as  the  Northern  Calcareous  Alps
(Reinecker & Lenhardt 1999; Neubauer & Genser 1989) and
within  the  Tauern  Window  (Wang  &  Neubauer  1998).  Ac-
tive  orogen-parallel  E-W  extension  can  be  observed  on  the
Brenner Normal Fault, on the western border of the Tauern
Window, in the Engadine and the Italian Eastern Alps (Reiter
et al. 2005).

Recent seismicity

The regional stress field caused by the indentation of the

Adria/Southalpine indenter is considered to control local pa-
leostress orientations of the Austroalpine and Penninic units
of the Eastern Alps along the western (e.g. Wang & Neubauer
1998)  and  eastern  parts  of  the  SEMP  fault  (Nemes  et  al.
1995). Further details are available from the Northern Calcar-
eous  Alps  (Linzer  et  al.  1997;  Peresson  &  Decker  1997a,b),
the southern Vienna Basin (Hinsch et al. 2005), and only a
few data are available from active tectonic structures in the
study  area.  Local  heterogeneities  and  discontinuities  in  up-
lift  and  incision  seem  to  play  a  major  role  (Reinecker  &
Lenhardt 1999) when considering the presence of active tec-
tonic structures in a region, situated along the SEMP fault.
Between  1900  and  1998,  more  than  1600  seismic  events
have been observed in Austria (Lenhardt et al. 2007) related
to some major active fault zones, including the SEMP fault.
Observations made during field work showed the instability
of  the  Ramsau  Conglomerate  Formation  and  the  instability
in the channels of the southern tributaries. Landslides are of-
ten delimited by fractures in the bedrock; an earthquake may
easily  trigger  spreading  of  unstable  lithologies.  Measure-
ments of fractures and faults as well as slickensides fortified
the assumption of recent neotectonic effects, or suggest that
earthquakes  occur  on  reactivated  faults  and  reflect  the  re-
gional stress field (Hinsch et al. 2005). The NE—SW short-
ening deduced from conjugate shear fractures of the Ramsau
Conglomerate  Formation  might  represent  the  surface  ex-
pression  of  an  earthquake-producing  stress  field.  This  is
consistent  with  stresses  deduced  from  fault  plane  solutions
from  earthquakes,  which  also  indicate  a  NE—SW  oriented
maximum  principal  stress.  These  orientations  of  maximum
horizontal  shortening  also  occur  in  paleostress  tensors  de-
duced  from  slickensides  within  the  basement  (see  above).
The  NE—SW  orientation  is  explained  by  the  NW-trending
edge of the rigid Bohemian spur.

Conclusions

The Upper Enns Valley covers only a small proportion of

the surrounding tectonic units, but it covers the typical fea-
tures of landforms, like valleys, escarpments, steep slopes

and plateaus used to interpret its present-day status. The fol-
lowing conclusions display the neotectonics, drainage pat-
tern and geomorphology of the Upper Enns Valley in a
regional context.

(1) The number of observed overprint on faults and striae

sets  derived  from  the  tributary  valleys  records  a  succession
of  four  stress  groups,  timed  from  Upper  Cretaceous  to
Pliocene,  comprising  N—S  compression,  E—W  extension,
NW—SE  compression  and  E—W  compression.  Thus,  the
present-day topography of the Upper Enns Valley is the re-
sult  of  changing  stress  fields,  of  activated  or  re-activated
events  along  the  SEMP  fault,  underlined  by  shallow  earth-
quakes occurring in the area. WNW—ESE extension indicat-
ed  on  a  mining  map  is  consistent  with  surface  observations
in the Ramsau Conglomerate Formation and with fault plane
solutions NNE of Salzburg.

(2) The predominant percentage of crystalline clasts in the

Ramsau Conglomerate Formation up to the Ramsau plateau
at ca. 1100 m and on Mitterberg at ca. 900 m indicates the
material supply from the Schladming basement terrain. The
Ramsau plateau and the Mitterberg count as relics and
formed a continuous Pleistocene valley bottom with the pa-
leosurfaces south of the Upper Enns Valley.

(3) Based upon the Ramsau Conglomerate Formation, the

Pleistocene valley bottom is informative to trace back inci-
sion and uplift rates. However, dating of the conglomerate is
still problematic. The so far published data about the age of
the lignite seam (31 ± 1.2 ka) which is intercalated in the
Ramsau Conglomerate Formation is disproved. The data do
not match with uplift and incision. An older age of the lignite
seam seems more realistic. The

C abundance is below de-

tection limit representing a

C-age older than 53,300 years.

An assumed age of deposition of the lignite ca. 120 ka BP in-
dicates a reasonable uplift/incision rate (2.4—3 mm/yr).

(4) Geomorphic units like steep slopes, high erosion rates

and the lithological differences between N and S of the Up-
per Enns Valley lead to a locally differential uplift history.

Acknowledgments: The manuscript profited substantially
from the detailed and constructive reviews of Wolfgang
Frisch and an anonymous reviewer. We gratefully acknowl-
edge Wolfgang Lenhardt for submitting earthquake data and
fault plane solutions. Acknowledgement is also given to the
Österreichische Geologische Gesellschaft.

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Appendix

Laboratory no.

Sample

1, 2)

[‰]

C-age

[BP]

VERA-5152 Ramsau

1 –30.4±1.7 >53,300

1σ — error

C-ratio determined by accelerator mass spectrometry

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Table 2:

Paleostress

the

basement:

Geographical

setting,

GPS

coordin

ates

when

available,

lithology

and

paleostress

tensors.

NDA

–

umerical

dynamical

analysis,

–

pressure-tension

method, R – stress ratio.

Locations are shown in Fig. 9.

eog

ithol

ogy

esp.

Form

ati

—

; NCA

—

)

aleostr

ess

tensor

oup

Met

σ1

σ 2

σ 3

150

of Irxner

hyl

lit

149

of M

andl

, R

ite

°2

460

3°

35.

869

320,

lei

-schi

, phyl

lit

336

320,

lei

-schi

, phyl

lit

260

320,

lei

-schi

, phyl

lit

296

320,

örfl

-schi

, phyl

lit

227

°2

986

3°

36.

907

lut

serberg

är

chenw

hyl

lit

190

°2

046

3°

35.

874

rubb

ach t

ren

ch r

igh

, l

igh

t do

ite

302

6 a

rubb

ach

, R

ite

153

4 26

rubb

ach

, R

ite

075

5 29

rubb

ach

, W

rst

n D

ite

152

rubb

ach

, R

ite

071

6 17

°2

196

3°

36.

184

rubb

ach,

ench

, R

sau D

ite

314

114/

°2

806

3°

45.

071

oad

Luse

r w

erf

, l

igh

t do

ite

166

oad

Luse

r w

erf

, l

igh

t do

ite

077

°2

800

3°

45.

948

rgst

, W

fen

orm

348

°2

164

3°

47.

252

raden

bach ri

ght

, l

igh

t do

ite

100

raden

bach ri

ght

, l

igh

t do

ite

240

raden

bach ri

ght

, l

igh

t do

ite

338

°2

051 E 13°

47.

268

raden

bach parki

, G

ten

n Li

est

one

065

raden

bach parki

, G

ten

n Li

est

one

340

°2

080

3°

47.

646

ichbe

, G

ten

n Li

est

one

260

ichbe

, G

ten

n Li

est

one

168

°2

813

3°

36.

848

eunegg

nnst

hyl

lit

047

9 27

°2

641

3°

37.

251

eunegg

Poi

ner

nnst

hyl

lit

051

eunegg

Poi

ner

nnst

hyl

lit

eunegg

“K

”

nnst

hyl

lit

237

penbach

nnst

hyl

lit

enschi

161

°2

393

3°

47.

739

sta

l P

lli

, g

hist

029

4 26

penbach

nnst

hyl

lit

enschi

201

Seew

l T

lsschl

uch

nnst

hyl

lit

uart

-chl

ori

347

°2

692

3°

52.

795

tten

nnst

hyl

lit

ori

-phyl

lit

221

itte

etw

röbm

ing and

ooshei

-schi

033

6 12