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Anne U. Reuther:

Surface exposure dating of glacial deposits from the last glacial cycle

Evidence from the Eastern Alps, the Bavarian Forest, the Southern Carpathians and the Altai Mountains

2007. 213 pages, 85 figures, 26 tables, 30 p. appendix, 17x24cm, 600 g
Language: English

(Relief Boden Palaeoklima, Band 21)

ISBN 978-3-443-09021-0, paperback, price: 68.00 €

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Keywords

surface exposure glacial deposit glacial cycle

Contents

Content Description top ↑

A major research goal in Quarternary sciences today is the reconstruction of past glacial fluctuations. Glacial deposits constitute an important terrestrial record of climate change. Linking the past athmospheric circulation pattern to terrestrial climate proxies is essential for an understanding of climate-glacier interaction. Surface exposure dating with cosmogenic nuclides produced in rock surfaces is an innovative technique for numerical dating of glacial landforms. Surface exposure dating has provided to be an invaluable tool for numerical dating of moraines. However, the surface exposure ages of moraine boulders cannot always be equated to the age of the landform. A detailed review of processes that affect moraine boulders in different glacial environments shows that precise exposure ages are more probably derived from small valley glaciers, whereas exposure ages from moraine boulders deposited in glacial environments where dead ice prevailed after deglaciation show a wide scatter in ages. Different interpretation models for surface exposure ages from moraines are summarized.

Bespr.: Erdkunde Bd. 62 Heft 4 (2008) top ↑

The actual publication of Reuther is a throughout revised and condensed version of her dissertation connected to a major research project on surface exposure dating between the Alps and the Altai. Consequently, it contains three main parts. The first part, covering about 40 pages, gives an introduction into the methodology, and general information about related calibration and interpretation. The second main part of the work contains the detailed results from the chosen study areas, presented separately in four chapters. Finally, a synthesis about the calculated former ELAs and the conclusions put the regional findings together to gain a more general outline for both, geochronological and methodological aspects. The appendix contains some detailed information about the individual samples and the dating procedure.

Surface exposure dating (SED) using in-situ produced cosmogenic nuclides (TCN), especially 10Be and 26Al, has become an important dating method to improve our knowledge about the Last Glacial Maximum (LGM) and Deglaciation, as well as it has been applied for the dating of Early Holocene and Neoglacial Little Ice Age-type events. A substantial number of samples have been dated in this study, and the methodological chapter starts with a short, but compact and profound description of this method and the necessary steps of sampling strategies, preparation and measurements of the samples taken. The style is appropriate even to those readers yet not familiar to TCN. A good part of the section of the book is dedicated to the problems of calibration and age interpretation of the results. Reuther stresses the possible influence of site-related factors (e.g. topographic shielding, vegetation cover, snow depths) upon the results and discussed the different calibration procedures in use. This allows the reader to make his own opinion about the potential errors and precision of the dates presented, and delivers some practical solutions for those readers applying SED using TCN by themselves. The importance of different glacial environments (e.g. small valley glaciers versus glaciers with ice-disintegration features and widespread dead-ice during the deglaciation process) for the age interpretation of the ages of moraine boulders is highlighted and an important general conclusion.

The chronological findings from the study areas show an overall good agreement with independent climatological evidence. The Würmian ice advances in the Bavarian Forest with LGM moraines formed between ca. 21 and 19 ka BP and ice recession starting around 17 ka BP coincides with the reported cold North Atlantic sea surface temperatures and the chronologies of neighbouring regions as e.g. the Eastern Alps. The results from the Southern Carpathians show some interesting new finding, e.g. a major Late-Glacial advance and a phase of increased aridity during LGM. In the Altai, Early-Würmian glacier advances and related extensive ice-dammed lakes compared to a suggested less dominant Late-Würmian glaciation clearly points towards the need of a more mass budget-based climatological interpretation of the Würmian climate and glaciations, as aridity and lack of precipitation seem to play an much more important role as purely temperature-based approaches might reveal.

In general, a typical German-style PhD thesis published as monograph often just achieves limited interest among potential readers due to its highly specialized subject. That is definitely not the case with Reuther’s work as it offers valuable information for both, those readers mainly interested in the methodological aspect of TCND and innovative solutions for the connected problems of calibration, and those readers focussed on the Quaternary itself and expecting new insights into the geochronology of the study areas. A good structure and professional layout make the work very readable and of unquestionable value for a broader audience. Only the price seems to be too high, especially for students and young scientists.

Stefan Winkler

Erdkunde Bd. 62 Heft 4 (2008)

Bespr.: Zeitschrift f. Geomorphologie N.F. 53/2 (2009) top ↑

Die Publikation hat das Anliegen, eine Einführung in die Oberflächenaltersdatierung mit Hilfe der kosmogenen Nuklide 10Be und 26Al zu geben. Die Analytik und die zur Altersberechnung führenden Methoden werden ausführlich beschrieben. Anwendungsbeispiele stammen aus dem Bayerischen Wald, den Ostalpen, den südlichen Karpaten und dem Altai-Gebirge. Dabei wurden jeweils Ablagerungen des letztglazialen Zyklus herangezogen. Es wurden Geschiebe aus Moränen und Findlinge datiert, wobei zu berücksichtigen ist, dass durch den Einfluss periglazialer Aktivitäten und durch Toteisaustauschprozesse nachträgliche Lage ver ände rungen stattgefunden haben können. Gletscherschliffe, die optimale Voraussetzungen für eine Oberflächenaltersdatierung bieten, waren in den untersuchten glazialen Ablagerungsgebieten nicht vorhanden.

Die Analysemöglichkeiten für die Bestimmung kosmogener Nuklide sind weltweit nur in wenigen Laboratorien vorhanden, so z. B. an der ETH Zürich, wo die Autorin die meisten ihrer Analysen unter Nutzung der AMS (accelerator mass spectrometry) durchführte. Mit Hilfe der kosmogenen Nuklide kann der Alterszeitraum bestimmt werden, während dessen die Oberflächen kosmogener Strahlung ausgesetzt gewesen sind. Dabei sind eine Reihe von störenden Einflussgrößen zu berücksichtigen wie die topographische Abschattung und die Vegetations- oder Schneebedeckung. Mit der Oberflächenaltersdatierung (surface exposure dating) eröffnet sich eine Möglichkeit der direkten Altersdatierung von Oberflächen, die in ihrer absoluten Aussagekraft den vielen indirekten Datierungsmethoden (Pollen, Warven, Bodenbildungen etc.) weit überlegen ist. Für die exemplarische Einführung wurden Beispiele ausgewählt, in denen, durch klassische Untersuchungen vorbereitet, bereits recht zuverlässige Chronologien vorlagen, in die sich die Ergebnisse der Oberflächendatierung sehr gut einpassen und die Zuverlässigkeit der Methode demonstrieren. Die Anwendung der Methode ist in der deutschen Geomorphologie bisher nur wenig verbreitet, und es ist der Autorin zu danken, dass sie mit dieser kompetenten Übersicht und Einführung den Weg für eine intensivere Nutzung bereitet hat.

K.-H. Schmidt, Halle

Zeitschrift für Geomorphologie N.F. 53/2 (2009)

Inhaltsverzeichnis top ↑

Foreword
Abstract
Zusammenfassung
Table of contents
Table of figures
Table of tables
Table of acronyms
1 Introduction and outline 20
1.1 General remarks 22
2 Surface exposure dating 24
2.1 Surface Exposure Dating - principles & calculation 24
2.1.1 Production of terrestrial in-situ cosmogenic nuclides 24
2.1.2 Factors that influence the site-specific production rate 32
2.1.3 Factors influencing the concentration of TCNs 37
2.2 Sampling, sample preparation and AMS measurement 41
2.2.1 Sampling strategies 41
2.2.2 Quartz purification 42
2.2.3 Nuclide extraction 44
2.2.4 AMS measurement and data reduction 49
2.3 A methodological study: Depth profile of subsurface nuclide production 50
2.3.1 Sampling site and methods 51
2.3.2 Results 54
2.3.3 Discussion and outlook 57
2.4 Interpretation of moraine age 58
2.4.1 Factors resulting in" too old" ages of moraine boulders 59
2.4.2 Factors resulting in 'too young' ages of moraine boulders 59
2.4.3 Importance of the glacial and climatic environment 60
2.4.4 Age models 63
2.4.5 Interpretation scheme 64
2.4.6 Summary and outlook 65
3 Study area: Bavarian Forest 67
3.1 Introduction 67
3.2 The study area 68
3.2.1 Geological setting of the study area 69
3.2.2 Climate and vegetation in the study area 69
3.2.3 Glaciation in the Bavarian Forest and the study area 70
3.2.4 Numerical age constraints of glacial deposits 72
3.3 Surface exposure dating - methods 72
3.4 Description of the sampling sites 76
3.5 Sample description and results of surface exposure dating 78
3.6 Interpretation and discussion of results 84
3.6.1 Würmian moraines 85
3.6.2 Grosser Arber summit 86
3.7 Conclusions and Outlook 88
4 Study area: Eastern Alps 90
4.1 Introduction 90
4.2 The study area 90
4.2.1 Geological setting of the study area in the Eastern Alps 91
4.2.2 Glaciation in the Eastern Alps 91
4.2.3 Late Würmian glaciation in the study area 93
4.2.4 Climate and Vegetation in the study area 96
4.2.5 Existing chronologies from the Northern Alps 96
4.3 Surface exposure dating of moraine boulders - methods 101
4.4 Sample description and results 103
4.5 Discussion of results 109
4.6 Conclusions and Outlook 116
5 Study area: Southern Carpathians 117
5.1 Introduction 117
5.2 The study area 117
5.2.1 Geological setting and soils 118
5.2.2 Climate and vegetation in the study area 119
5.2.3 Glaciation 120
5.3 Methodology 123
5.3.1 Mapping and surveying of glacial landforms 123
5.3.2 Surface exposure dating 124
5.3.3 Pedological investigations 127
5.4 Results and Interpretation 128
5.4.1 Mapping and landform survey 128
5.4.2 Surface exposure dating - results and interpretation 129
5.4.3 Pedological investigations - results and interpretation 134
5.5 Discussion 139
5.6 Conclusions and outlook 142
6 Study area: Altai mountains 144
6.1 Introduction 144
6.2 The Russian Altai mountains 144
6.2.1 Geology 145
6.2.2 Climate 147
6.2.3 Vegetation and soil 147
6.2.4 Glaciation in the Altai mountains 148
Glaciation in the Gorny Altai 148
Ice-dammed lakes in the Chuya and Kuray basin 150
6.3 Absolute age constraints 154
6.4 Surface exposure age dating in the Altai mountains 158
6.5 Exposure dating of the most recent cataclysmic flood 161
6.5.1 Sampling locations related to the most recent cataclysmic flood event 161
6.5.2 Results and interpretation of exposure ages related to the most recent
cataclysmic flood 163
6.6 Exposure dating of glacial advances in the Altai mountains 166
6.6.1 Sampling locations with regard to glacial advances in the study area 166
6.6.2 Postflood glacial advance 167
6.6.3 Glacial advances that occurred prior to the most recent flood 167
6.6.4 Results and interpretation of glacial deposits in the study area 169
6.7 Discussion of the late Zyryanka in the Altai mountains 173
6.8 Conclusion and outlook 176
7 Equilbrium line altitude of the study areas 178
7.1 Introduction 178
7.2 Theory - ELA determination 178
7.3 ELA determination and ELA depression in the study areas 179
7.3.1 Eastern Alps 179
7.3.2 Bavarian Forest 180
7.3.3 Southern Carpathians 181
7.3.4 Altai mountains 181
7.4 Comparison of ELAs from the study areas 182
8 Discussion, conclusion and outlook 184
8.1 Methodology 184
8.1.1 Outlook 185
Table of contents 10
8.2 Local chronologies 185
References 192
Appendix A - Calculation of topographic shielding using a GIS
Appendix B - Topographic shielding for each boulder and geographic coordinates
Appendix C - Results of elution curves
Appendix D - Thin sections of selected samples
Appendix E - Data of field work in the Pietrele valley