CLIMATIC CONDITIONS AND SEDIMENTARY PROCESSES …...climatic conditions and sedimentary processes...
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CLIMATIC CONDITIONS AND SEDIMENTARY PROCESSES DURING MIS 5 IN INNERALPINE VALLEYS (TYROL / EASTERN ALPS / AUSTRIA) Introduction Jürgen M. REITNER & Ilse DRAXLER Geological Survey of Austria [email protected] & [email protected] Geologische Bundesanstalt, Neulinggasse 38, A-1030 Wien Detailed information about vegetation and climate change during MIS 5 in the Eastern Alps is available from key sites like the lacustrine archives of Samerberg (GRÜGER 1979) and Mondsee (DRESCHER-SCHNEIDER, 2000). However, our knowledge of the impact of these changing conditions on the depositional processes especially in the alpine valleys is very limited. The valley of Kitzbühel (800-600 m a.s.l.) and the adjacent small basin of Hopfgarten (900-600 m a.sl.) in Tyrol are surrounded by up to 2300 m high mountains. D hese areas were covered by ~ 1200 m thick icestreams. The study is a result of detailed geological mapping (J.R.) and following sedimentological investigations (J.R.) and palynological analyses (I.D.). uring the Last Glacial Maximum (LGM, MIS 2) t The investigation area (Kitzbühel - St. Johann - Hopfgarten) during the Last Glacial Maximum (LGM; MIS 2) (from VAN HUSEN, 1987) The Salzach valley separates the investigation area from the mountain range of the Hohe Tauern (up to 3800 m a.s.l.), where a very limited glaciation still exists. The Pass Thurn (1274 m a.s.l.) was the lowest ice transfluence towards the north during LGM. Field evidence PROFILE SCHÖNBACHTAL (HOPFGARTEN) The up to 130 m thick pre-LGM valley fill consists mainly of coarse fluvial gravels with intercalated lignites associated with alluvial fan and overbank deposits. According to pollen analyses of the lignites two interstadials with wood vegetation can be distin- guished: The Brørup or 1 Würmian Interstadial (Picea, Pinus, Abies, Fagus; MIS 5c) and the Odderade or 2 Würm Interstadial (Picea, Pinus, Abies; Odderade; MIS 5c). The thick gravel layers (braided river sediments) below and between the lignites represent the cold 1. and 2. Early Würmian Stadial (MIS 5d and 5b). Overbank deposits associated with the gravels provide evidence of a treeless envi- ronment during the fluvial accumulation of MIS 5b. The main accumulation happened during the cold stadials of the Early Würmian (MIS 5d & 5b) by braided rivers. At that time the extent of the local glaciers was much smaller than during their maximum-position in the Würmian-Lateglacial. This restricted glaciation is in contrast to the results of PREUSSER et al. (2003) from Switzerland, who argue for a pronounced glacial advance into the Alpine foreland. st nd HOPFGARTEN BASIN The sequence starts with the basal till and sediments (banded clay) of Termination II (both MIS 6). The following lignites (in St. Johann) associated with alluvial cone and overbank deposits indicate an environment similar to today's situation, with partly prograding alluvial cones and peat growth in their backwater. The pollen content shows forest vegetation with dominance of spruce (Picea) and up to 20 % fir (Abies) indicating the last Interglacial (Eemian; MIS 5e). Overlying alluvial fan deposits are attributed to the cold phase of the 1. Würm Stadial (MIS 5d). Lignites (St. Johann & Kitz- bühel) and silts with wood (Aurach), again in association with fan deposits, were deposited in the arboreous environment (mostly Picea) of the 1. Würm-Interstadial (Brørup; MIS 5c). A lignite age of 90 ± 8 ka of a drill core from Kitzbühel-Lebenberg dated by U/Th (BORTENSCHLAGER, unpublished) supports this classification. VALLEY OF KITZBÜHEL As during the Holocene (s. PATZELT, 1994) prograding alluvial fans block main valley and cause deposition of flood material in the swampy intercone areas, where peat growths. Morphology of the Hopfgarten Basin PROFILE KITZBÜHEL-LEBENBERG (East) Stratigraphy of the valley of Kitzbühel (Aurach, Kitzbühel, St. Johann) and the Hopfgarten Basin in comparison with the evidences of Samerberg (GRÜGER, 1979), Mondsee (DRESCHER- SCHNEIDER, 2000) and the Inn valley (FLIRI, 1973). Speleothem data are according to SPÖTL et al. (2002). The Würmian Chronostratigraphy is given by CHALINE & JERZ (1984). The age of Marine Isotope Stage (MIS) 5e (MARTINSON et al., 1987) is modified according to SHACKLETON et al. (2002). Vegetation: PIC - Picea (spruce), PIN - Pinus (pine), ABIES (fir), FAGUS (beech), CORY - Corylus (hazel),CARP - Carpinus ( hornbeam), QUERCUS (oak), TAXUS (yew). The interglacial and interstadial environments are comparable to those of the Holocene with overbank sedimentation and peat accumulation in the swampy backwater of alluvial fans. Despite the glacial erosion during the Last Glacial Maximum (LGM, MIS 2) quite extensive sedimentary records of MIS 5 with lignites, overbank sediments, alluvial fan deposits and fluvial gravels are preserved in the inneralpine valleys. An arboreous environment is evidenced for the Last Interglacial (Eemian;MIS 5e) and the Early Würmian Interstadials Brørup (MIS 5c) and Odderade (MIS 5a). For the Brørup site of Kitzbühel a lignite age of 90 ± 8 ka dated by U/Th supports the palynological classification. The main accumulation happened during the cold Stadials of the Early Würmian (MIS 5d & MIS 5b) by braided rivers. At that time the glaciers didn't reach the valleys of the investigation area and thus only a limited glaciation existed in the Eastern Alps. CHALINE, J. & JERZ H., 1984: Arbeitsergebnisse der Subkommission für Europäische Quartärstratigraphie - Stratotypen des Würm-Glazials.- Eiszeitalter u. Gegenwart, 35, 185 206, Hannover. DRESCHER-SCHNEIDER, R., 2000: Die Vegetations- und Klimaentwicklung im Riß/Würm-Interglazial und im Früh- und Mittelwürm in der Umgebung von Mondsee. Ergebnisse der pollenanalytischen Untersuchungen. - Mitt. Komm.Quartärforsch. Österr. Akad. Wiss., 12, 39-92, Wien. FLIRI, F, 1973: Beiträge zur alpinen Würmvereisung: Forschungen am Bänderton von Baumkirchen (Inntal, Nordtirol).- Z. Geomorph., N.F. Suppl., 16, 1-14.. GRÜGER E. (1979): Spätriss, Riss/Würm und Frühwürm am Samerberg in Oberbayern ein vegetationsgeschichtlicher Beitrag zur Gliederung des Jungpleistozäns.- Geologica Bavarica, 80, 5-64, Munich MARTINSON, D.G., PISIAS, N.G., HAYS, J.D., IMBRIE, J., MOORE, T.C. & SHACKLETON, N.J., 1987:Age dating and the orbital thory of the ice ages: development of a high resolution 0 to 300,000-year chronostratigraphy.- Quaternary Research, 27, 1-29. PATZELT, G., 1994: Holocene development of alluvial fans and the floor of the Inn Valley.- Mountain Research and Development, 14, 283-284 PREUSSER, F., GEYH, M.A. & SCHLÜCHTER, CH. (2003): Timing of Late Pleostocene Climate in Lowland Switzerland.- Quat. Science Rev. 22/14, 1435-1445. SPÖTL, C., MANGINI, A., FRANK, N., EICHSTÄDTER, R. & BURNS, S.J., 2002: Start of the last interglacial period at 135 ka: Evidence from a high alpine speleothem. Geology, 30, 815-818. SHACKLETON, N.J., CHAPMAN, M. SANCHEZ.GONI, M.F., PAILLER, D., LANCELOT,Y., 2000: The Classic Marine Isotope Substage 5e.- Quaternary Research, 58, 14-16. VAN HUSEN, D., 1983: A model of valley bottom sedimentation during climatic changes in a humid alpine environment.- In: EVENSON, E. B., SCHLÜCHTER, Ch. & RABASSA, J. (ed.): Tills and Related Deposits.- 341-344, Balkema, Rotterdam. Conclusions Kitzbühel St. Johann i. T. Kufstein Hopfgarten Hohe Tauern Salzach Valley Inn Valley Pass Thurn FACIES MODEL FOR THE INTERSTADIAL AND INTERGLACIAL DEPOSITS trees & shrubs herbs trees & shrubs herbs 12,09 m 12,79 m 14,39 m 15,69 m after VAN HUSEN, 1983 References SECTION ALONG THE VALLEY OF KITZBÜHEL SECTION ALONG THE VALLEY OF THE HOPFGARTEN BASIN The pollen record of the section Kitzbühel-Lebenberg (east) with high per- centages of arboreal pollen represents well developed coniferous forests. At the base the sequence is dominated by Pinus and Betula with stands of Pinus cembra and Larix and scarce occurrence of shrubs (Juniperus, Hippophae, Salix) and steppe elements (Artemisia, Chenopodiaceae). This plant community is replaced after reforestation by a coniferous forest dominated by Picea with decidous trees. Alnus (local habitat) and the light de-manding Corylus (hazel) are present together with the limited but regu- larly occurrence of the thermophilous arboreal taxa Ulmus, Tilia, Quercus and Fraxinus. The parallel sequence of the drill core Kitzbühel-Lebenberg (BORTEN- SCHLAGER, unpublished) with the U/Th age of 90 8 ka shows the same development of vegetation. decidous ±
Transcript of CLIMATIC CONDITIONS AND SEDIMENTARY PROCESSES …...climatic conditions and sedimentary processes...
CLIMATIC CONDITIONS AND SEDIMENTARY PROCESSES DURING MIS 5
IN INNERALPINE VALLEYS (TYROL / EASTERN ALPS / AUSTRIA)
Introduction
Jürgen M. REITNER & Ilse DRAXLERGeological Survey of Austria
[email protected] & [email protected]
Geologische Bundesanstalt, Neulinggasse 38, A-1030 Wien
Detailed information about vegetation and climate change during MIS 5 in the Eastern Alps is
available from key sites like the lacustrine archives of Samerberg (GRÜGER 1979) and Mondsee
(DRESCHER-SCHNEIDER, 2000). However, our knowledge of the impact of these changing conditions
on the depositional processes especially in the alpine valleys is very limited.
The valley of Kitzbühel (800-600 m a.s.l.) and the adjacent small basin of Hopfgarten (900-600 m a.sl.)
in Tyrol are surrounded by up to 2300 m high mountains.
D hese areas were covered by ~ 1200 m thick icestreams.
The study is a result of detailed geological mapping (J.R.) and following sedimentological
investigations (J.R.) and palynological analyses (I.D.).
uring the Last Glacial Maximum (LGM, MIS 2) tThe investigation area (Kitzbühel - St. Johann - Hopfgarten)during the Last Glacial Maximum (LGM; MIS 2)(from VAN HUSEN, 1987)
The Salzach valley separates the investigation area fromthe mountain range of the Hohe Tauern (up to 3800 m a.s.l.),where a very limited glaciation still exists.The Pass Thurn (1274 m a.s.l.) was the lowest ice transfluencetowards the north during LGM.
Field evidence
PROFILE SCHÖNBACHTAL (HOPFGARTEN)
The up to 130 m thick pre-LGM valley fill consists mainly of coarse fluvial gravels with intercalated
lignites associated with alluvial fan and overbank deposits.
According to pollen analyses of the lignites two interstadials with wood vegetation can be distin-
guished:
The Brørup or 1 Würmian Interstadial (Picea, Pinus, Abies, Fagus; MIS 5c) and the Odderade
or 2 Würm Interstadial (Picea, Pinus, Abies; Odderade; MIS 5c). The thick gravel layers (braided
river sediments) below and between the lignites represent the cold 1. and 2. Early Würmian Stadial
(MIS 5d and 5b). Overbank deposits associated with the gravels provide evidence of a treeless envi-
ronment during the fluvial accumulation of MIS 5b.
The main accumulation happened during the cold stadials of the Early Würmian (MIS 5d & 5b) by
braided rivers. At that time the extent of the local glaciers was much smaller than during their
maximum-position in the Würmian-Lateglacial. This restricted glaciation is in contrast to the results
of PREUSSER et al. (2003) from Switzerland, who argue for a pronounced glacial advance into the
Alpine foreland.
st
nd
HOPFGARTEN BASIN
The sequence starts with the basal till and sediments (banded clay) of Termination II (both MIS 6).
The following lignites (in St. Johann) associated with alluvial cone and overbank deposits indicate
an environment similar to today's situation, with partly prograding alluvial cones and peat growth
in their backwater. The pollen content shows forest vegetation with dominance of spruce (Picea)
and up to 20 % fir (Abies) indicating the last Interglacial (Eemian; MIS 5e). Overlying alluvial fan
deposits are attributed to the cold phase of the 1. Würm Stadial (MIS 5d). Lignites (St. Johann & Kitz-
bühel) and silts with wood (Aurach), again in association with fan deposits, were deposited in the
arboreous environment (mostly Picea) of the 1. Würm-Interstadial (Brørup; MIS 5c). A lignite age of
90 ± 8 ka of a drill core from Kitzbühel-Lebenberg dated by U/Th (BORTENSCHLAGER, unpublished)
supports this classification.
VALLEY OF KITZBÜHEL
As during the Holocene (s. PATZELT, 1994) prograding alluvial fans blockmain valley and cause deposition of flood material in the swampyintercone areas, where peat growths.
Morphology of the Hopfgarten Basin
PROFILE KITZBÜHEL-LEBENBERG (East)
Stratigraphy of the valley of Kitzbühel (Aurach, Kitzbühel, St. Johann) and the Hopfgarten Basinin comparison with the evidences of Samerberg (GRÜGER, 1979), Mondsee (DRESCHER-SCHNEIDER, 2000) and the Inn valley (FLIRI, 1973). Speleothem data are according to SPÖTL etal. (2002). The Würmian Chronostratigraphy is given by CHALINE & JERZ (1984). The age ofMarine Isotope Stage (MIS) 5e (MARTINSON et al., 1987) is modified according to SHACKLETONet al. (2002).Vegetation: PIC - Picea (spruce), PIN - Pinus (pine), ABIES (fir), FAGUS (beech), CORY - Corylus
(hazel),CARP - Carpinus ( hornbeam), QUERCUS (oak), TAXUS (yew).
The interglacial and interstadial environments are comparable to those of the Holocene with
overbank sedimentation and peat accumulation in the swampy backwater of alluvial fans.
Despite the glacial erosion during the Last Glacial Maximum (LGM, MIS 2) quite extensive
sedimentary records of MIS 5 with lignites, overbank sediments, alluvial fan deposits and fluvial
gravels are preserved in the inneralpine valleys.
An arboreous environment is evidenced for the Last Interglacial (Eemian;MIS 5e) and the Early
Würmian Interstadials Brørup (MIS 5c) and Odderade (MIS 5a). For the Brørup site of Kitzbühel
a lignite age of 90 ± 8 ka dated by U/Th supports the palynological classification.
The main accumulation happened during the cold Stadials of the Early Würmian (MIS 5d & MIS 5b)
by braided rivers. At that time the glaciers didn't reach the valleys of the investigation area and
thus only a limited glaciation existed in the Eastern Alps.
CHALINE, J. & JERZ H., 1984: Arbeitsergebnisse der Subkommission für Europäische Quartärstratigraphie - Stratotypen des Würm-Glazials.-Eiszeitalter u. Gegenwart, 35, 185 206, Hannover.
DRESCHER-SCHNEIDER, R., 2000: Die Vegetations- und Klimaentwicklung im Riß/Würm-Interglazial und im Früh- und Mittelwürm in der Umgebung vonMondsee. Ergebnisse der pollenanalytischen Untersuchungen. - Mitt. Komm.Quartärforsch. Österr. Akad. Wiss., 12, 39-92, Wien.
FLIRI, F, 1973: Beiträge zur alpinen Würmvereisung: Forschungen am Bänderton von Baumkirchen (Inntal, Nordtirol).- Z. Geomorph., N.F. Suppl., 16, 1-14..GRÜGER E. (1979): Spätriss, Riss/Würm und Frühwürm am Samerberg in Oberbayern ein vegetationsgeschichtlicher Beitrag zur Gliederung des
Jungpleistozäns.- Geologica Bavarica, 80, 5-64, MunichMARTINSON, D.G., PISIAS, N.G., HAYS, J.D., IMBRIE, J., MOORE, T.C. & SHACKLETON, N.J., 1987: Age dating and the orbital thory of the ice ages:
development of a high resolution 0 to 300,000-year chronostratigraphy.- Quaternary Research, 27, 1-29.PATZELT, G., 1994: Holocene development of alluvial fans and the floor of the Inn Valley.- Mountain Research and Development, 14, 283-284PREUSSER, F., GEYH, M.A. & SCHLÜCHTER, CH. (2003): Timing of Late Pleostocene Climate in Lowland Switzerland.- Quat. Science Rev. 22/14, 1435-1445.SPÖTL, C., MANGINI, A., FRANK, N., EICHSTÄDTER, R. & BURNS, S.J., 2002: Start of the last interglacial period at 135 ka: Evidence from a high alpine
speleothem. Geology, 30, 815-818.SHACKLETON, N.J., CHAPMAN, M. SANCHEZ.GONI, M.F., PAILLER, D., LANCELOT, Y., 2000: The Classic Marine Isotope Substage 5e.- Quaternary
Research, 58, 14-16.VAN HUSEN, D., 1983: A model of valley bottom sedimentation during climatic changes in a humid alpine environment.- In: EVENSON, E. B.,
SCHLÜCHTER, Ch. & RABASSA, J. (ed.): Tills and Related Deposits.- 341-344, Balkema, Rotterdam.
Conclusions
Kitzbühel
St. Johann i. T.
Kufstein
Hopfgarten
Hohe Tauern
SalzachValley
InnValley
Pass Thurn
FACIES MODEL FOR THE INTERSTADIAL AND INTERGLACIAL DEPOSITS
trees
&sh
rubs
herb
s
trees
&sh
rubs
herb
s
12,09 m
12,79 m
14,39 m
15,69 m
after VAN HUSEN, 1983
References
SECTION ALONG THE VALLEY OF KITZBÜHEL
SECTION ALONG THE VALLEY OF THE HOPFGARTEN BASIN
The pollen record of the section Kitzbühel-Lebenberg (east) with high per-centages of arboreal pollen represents well developed coniferous forests.At the base the sequence is dominated by Pinus and Betula with stands ofPinus cembra and Larix and scarce occurrence of shrubs (Juniperus,Hippophae, Salix) and steppe elements (Artemisia, Chenopodiaceae).This plant community is replaced after reforestation by a coniferous forestdominated by Picea with decidous trees. Alnus (local habitat) and the lightde-manding Corylus (hazel) are present together with the limited but regu-larly occurrence of the thermophilous arboreal taxa Ulmus, Tilia,Quercus and Fraxinus.The parallel sequence of the drill core Kitzbühel-Lebenberg (BORTEN-SCHLAGER, unpublished) with the U/Th age of 90 8 ka shows the samedevelopment of vegetation.
decidous
±
