From the foreland to the Central Alps

160 Pages·2014·26.86 MB·English

by  Hanns Kerschner

DEUQUA exCursions
Edited by Hanns Kerschner, Karl Krainer and Christoph Spötl
From the foreland to the Central Alps
Field trips to selected sites of Quaternary research
in the Tyrolean and Bavarian Alps
GEOZON

From the foreland
to the Central Alps

Preface
The Tyrolean and Bavarian Alps offer a fascinating plethora of Quaternary issues ranging from outcrops of Pleistocene sedi-
ment successions to modern glacial and periglacial environments. Twelve such areas were selected and are part of this field
guidebook, the first of its kind for the Quaternary in this part of the Alps.

Produced for the 2014 convention of the German Quaternary Association (DEUQUA) this book was published in English to
allow also the non-German speaking colleagues, students and interested lay people to visit these field areas and to access this
information. Many sites including the Hötting Breccia and its well-known flora, the banded clays of Baumkirchen and the
Gschnitz and Egesen glacier advances, to name just a few, are key to the understanding of the Quaternary history and dy-
namics of the entire Alps including their foreland. We express our hopes that this guidebook will foster further international
collaboration in and across this fascinating mountain range, its multifaceted Quaternary evolution and landscape evolution.

We extend our gratitude to all authors who contributed to this book, to Andrew Moran for carefully checking and improving
English style and grammar, to Sascha Fricke for his professional support and collaboration, and to the sponsors who made
it possible to publish this as a full-colour and open-access book.
5
Innsbruck
Excursion A
The Rosenheim Basin: Würmian and Pre-Würmian deposits and the
A
Höhenmoos interglacial (MIS 7)
Das Rosenheimer Becken: Würm- und Präwürmzeitliche Ablagerungen
und das Höhenmoos Interglazial (MIS 7)
Martin Herz, Maria Knipping, Ernst Kroemer
Fig. 1: Map of Bavaria showing the excursion area (red rectangle). M. Munich.
Abb. 1: Karte von Bayern mit Exkursionsgebiet (rot umrandet). M. München.
6
Excursion A ¬ Innsbruck
A
Fig. 2: Simplified geological map
with listed stops. 1 = view point
Törwang – Aussichtskapelle -
Overview of the Rosenheim Basin
and the Inn Valley. 2 = The Eemian
lake sediments of Samerberg. 3 =
Lateglacial delta sediments of the
late Würmian Lake Rosenheim –
Gravel pit Grad Nagelfluhwerk,
Brannenburg. 4 = Delta conglom-
erates of the Rissian Lake Rosen-
heim at quarry Grad Nagelfluh-
werk, Brannenburg and foresets of
the Delta conglomerates at quarry
Anton Huber, Brannenburg. 5 =
The interglacial of Höhenmoos
(MIS 7).
Abb. 2: Vereinfachte geologische
Karte mit den Exkursionshalten.
1 = Aussichtspunkt Törwang –
Aussichtskapelle – Übersicht über
das Rosenheimer Becken und das
Inntal. 2 = Eemzeitliche Seeab-
lagerungen des Samerberg. 3 =
Spätglaziale Deltaablagerungen
des spätwürmzeitlichen Rosenhei-
mer Sees, Kiesgrube Nagelfluhwerk
Brannenburg. 4 = Deltakonglo-
merate des rißzeitlichen Rosen-
heimer Sees im Steinbruch Grad
Nagelfluhwerk, Brannenburg und
„foresets“ der Deltakonglomerate
im Steinbruch Anton Huber, Bran-
nenburg. 5 = Das Interglazial von
Höhenmoos (MIS 7).
1 Introduction basin, which are mainly found in areas of steep river and
On this field trip new results of the extensive mapping pro- creek slopes. Due to the location in the upturned part of the
gram (IOGI) performed by the Bavarian Geological Survey Molasse, the wide range of sediments from the Lower Fresh-
of the Bavarian Environmental Agency are presented. Figure water Molasse to the Upper Marine- and finally to the Upper
1 shows the excursion area in southern Bavaria southeast of Freshwater Molasse can be seen in the outcrops from South
Munich. Fig. 2 shows a simplified geological map of the field to North. South of the fault and underneath the Quaternary,
trip area based on the work of Wolf (1973), Ganss (1980), nappes of the Helvetic (light green), the Flysch (darker green)
Kunz et al. (2013) and Kroemer et al. (in press). and the Northern Calcareous Alps (light brown) are present.
The light blue color, mostly on the western part of the Between these sedimentary basement rocks and the
map, shows the extent of the former Lateglacial lake, which Würmian and Holocene deposits, which cover most of the
filled the Rosenheim Basin after the retreat of the Inn Gla- area, there are – marked by red areas and dots – Quaternary
cier. In the northern part the remains of this big lake (todays glacial and interglacial deposits. It looks as though in some
Simssee) can be identified in a SW–NE trending sub-basin. parts, the pre-Würmian landscape with its hills and valleys
Today this area is dominated by fine-grained lake sediments, is buried beneath the younger sediments and is therefore
in wide parts covered with peat, and along the Inn, by coarse somehow preserved. But to our current knowledge, the re-
grained river gravels. These deposits were formed after the lationship between these individual deposits is not clear, es-
basin was drained at the end of the Lateglacial and during pecially because unambiguous stratigraphical data is not yet
the Holocene. available.
The eastern part of the map is mostly covered by a light
grey colour, which represents glacial and fluvioglacial sedi- 2 Excursion
ments of Würmian age. Only limited parts in the small val-
leys and depressions are covered by Holocene sediments and Stop 1: Törwang – Aussichtskapelle – Overview of the
peats. In the central part of this area a depression between Inn Valley
Rohrdorf in the West and Frasdorf in the East is developed.
This depression, in which the Autobahn A8 was built, fol- The first stop of the field trip is the view point from a little
lows the main fault, which divides the folded part of the Alps chapel (Aussichtskapelle) outside of Törwang. The stop will
in the South from the unfolded part in the north. The yel- permit a short geological and geomorphological introduc-
low colour in the North represents sediments of the Molasse tion to the Rosenheim basin and its eastern surroundings.
7
Excursion A ¬ Innsbruck
A
Fig. 3: Panorama of the Rosenheim Basin; View to the West and North.
Abb. 3: Panorama des Rosenheimer Beckens, Blick nach Westen und Norden.
First we will take a look to the West and North into the the steep embankments of the creeks and small rivers. Most
glacially over-deepened basin of Rosenheim and the Inn Val- of the surface, however, is covered by Würmian till, glacio-
ley. The continuous line of the horizon represents more or less fluvial meltwater sediments and glacial lake deposits, which
the Würmian outer moraines of the Inn Glacier, which encir- themselves often contain, especially in surface depressions,
cle the basin. The city of Rosenheim is located at the center of peat sediments. During geological mapping we found sedi-
the basin. At the end of the Würmian Pleniglacial and during ments, mostly in the form of buried valley fills of pre-Würm-
the Lateglacial, the depression was occupied by former Lake ian age. These outcrops are commonly small, some only 10
Rosenheim. The lake level once reached up to the plane of the to 100 m in length and a few metres in height. Some of the
delta of Rohrdorf and the Samerberg rest area located along sediments might also be regarded as glacial in origin, but
Autobahn A8. To the North, the former shore can be followed others contain a reasonable amount of organic matter and
along the fir woods up to the basin of Simssee, which was fossils. Later we will see an example of this (Stop 5), in a
once also part of a much bigger water shed. Due to erosion, creek east of the little village of Höhenmoos.
the lake level today is about 10 m deeper. According to the To the South, the peaks and tops of the Northern Calcare-
new mapping results and the evaluation of the digital terrain ous Alps form an impressive panorama with Hochries (1588
model, the former lake level rises from the north (delta of m a.s.l.) and Heuberg (1338 m a.s.l.) constituting the high-
Edling ca. 480 m a.s.l.) to the south (beach terraces of Kief- est elevations. In the foreground in front of the mountains
ersfelden ca. 490 m a.s.l.) by about 10 m. The reasons for this another depression in the terrain developed. The so-called
are not completely understood at the moment, but isostatic or basin of Törwang – Gernmühl was formed by a branch of
tectonic processes or a combination of both likely play a role. the Inn Glacier. It is filled by a sequence of diamicts and lake
As mentioned earlier, the basement of the hills is built sediments. In the 1950s to the 1970s Proebstl recognized the
up by Molasses deposits. The outcrops of these Tertiary sedi- interglacial and interstadial character of parts of these fine
ments and sedimentary rocks are more or less restricted to grained sediments.
Fig. 4: Panorama to the Northeast:
The hills between Simssee and the
depression of Rohrdorf Frasdorf
north of the Alpine front.
Abb. 4: Panorama Blick nach Nord-
osten: Die Hügel zwischen dem Sims-
see und der Furche Rohrdorf Frasdorf
nördlich der Alpenfront.
8
Excursion A ¬ Innsbruck
A
Fig. 5: Panorama to the South: The Northern Calcareous Alps and the depression of Törwang – Gernmühl.
Abb. 5: Panorama Blick nach Süden: Die Nördlichen Kalkalpen und die Eintiefung von Törwang – Gernmühl.
Stop 2 : Eemian lake sediments of Samerberg performed (Jerz 1983). The palynological work was carried
out by Grüger (1979 and 1983), who identified two intergla-
After decades of research Proebstl described in detail the cials. He considered the lower warm period as equivalent of
geological setting of the Eemian Interglacial, as well as the the Holsteinian (MIS 9 or 11) and the upper one as Eemian
early Würmian Interstadial and late Würmian sediments (MIS 5).
(Proebstl 1982). Besides a sedimentological description of The goal of the stop at the Samerberg is to gain a view
the outcrops, the author also listed the faunal and herbal in- of the outcrop(s) of the Eemian interglacial lake sediments,
ventory. In 1973 the Samerberg 1 core (SAM1) was drilled by especially with respect to the second outcrop of interglacial
the Bavarian Geological Survey (Jerz 1980). It was followed sediments at Höhenmoos.
(1974/1975) by geophysical research (Jerz et al. 1979, Baad-
er 1983), which found that the NE-SW extended Törwang Stop 3: Lateglacial delta sediments of the late Würmian
– Gernmühl basin has a length of about 4 km, is up to 1 km Lake Rosenheim at the gravel pit Grad Nagel-
wide and up to 100 m deep. The nose of the Moosen divides fluhwerk, Brannenburg.
the basin in two parts: The Törwang subbasin in the North
and the Gernmühl subbasin in the South. The main drainage Lake Rosenheim has a long and ongoing history of investiga-
occurs via the Achen stream. In the South, the Gernmühl tions with Penck & Brückner (1901–1909) and Troll (1924)
Basin is fed by three inlets: Hundsgraben, Weißen- and Flud- as the most prominent regional workers. Regional mapping
erbach. In 1981 a second drilling, “Samerberg 2” (SAM2), was on different map sheets (scale 1 : 25 000) was conducted by
Fig. 6: In this slightly modified part of the geological map sheet 8239 Aschau (Gans 1980) the extent of the Törwang – Gernmühl basin is indicated by the
dashed blue line. The red points SAM1 und SAM2 mark the locations of the scientific drilling sites and the outcrops of fine grained lake sediments are
represented in orange.
Abb. 6: In dem gering veränderten Ausschnitt der Geologischen Karte Blatt 8239 Aschau (Gans 1980) ist die Ausdehnung des Törwang – Gernmühler
Beckens durch die gestrichelte blaue Line angezeigt. Die roten Punkte SAM1 und SAM 2 markieren die Bohransatzpunkte der Forschungsbohrungen. Die
Aufschlüsse der feinkörnigen Seesedimente sind in orange eingetragen.
9
Excursion A ¬ Innsbruck
A
Fig. 7: Extent of Lateglacial Lake
Rosenheim (blue) and shoreline
features (magenta).
Abb. 7: Ausdehnung des spätgla-
zialen Rosenheimer Sees (blau)
und Uferbildungen (magenta).
Fig. 8: The gravel pit Grad exposes
delta sediments deposited by local
mountain creeks (Grießenbach
and others) into former Lake
Rosenheim.
Abb. 8: In der Kiesgrube Grad
sind Deltaablagerungen auf-
geschlossen, die durch lokale
Gebirgsbäche (Grießenbach und
andere) in den ehemaligen Rosen-
heimer See geschüttet wurden.
Wolff (1973, the Quaternary research was partly done by H. implications of isostatic movement by using Lidar data.
Jerz), Kunz et al. (2013a, 2013b), Kroemer et al. (in press), During the geological mapping of the central area of the
and Wallner (2011a, 2011b, 2011c, 2011d). Veit (in Wolff Rosenheim basin (Kunz et al. 2013a, 2013b, Kroemer et al.,
1973, p. 283) presented a map showing the thickness of the in press) the question about the extent of the Lateglacial
late Würmian lake sediments. Kroemer (2011) estimated the Lake Rosenheim was raised. The existing map and interpre-
extent of Lake Rosenheim to about 450 km² and pointed out tation of the lake and surrounding sediments (Troll 1924,
10
Excursion A ¬ Innsbruck