Using in-situ cosmogenic 36Cl exposure dating of glacial erratics to establish a retreat chronology of the Iller Piedmont Glacier (Southern Germany)

Dominic Hildebrandt1,4, Florian Hofmann1,5, Silke Merchel2,3, Georg Rugel2, Johannes Lachner2, Martin Martschini3, Anke Maria Friedrich1

1Department of Earth & Environmental Sciences, Ludwig Maximilian University Munich, Ludwig Maximilian University Munich, Munich, Germany, 2Department Accelerator Mass Spectrometry and Isotope Research, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany, 3University of Vienna, Faculty of Physics, Isotope Physics, Vienna, Austria, 4Present address: Department of Earth Sciences, ETH Zurich, Zurich, Switzerland, 5Present address: Department of Earth Sciences, University of Southern California, Los Angeles, USA

The dynamic behavior of glacial retreat following the globally diachronous Last Glacial Maximum (LGM) is poorly understood. In the Northern Alpine Foreland, multiple lobes of foreland glaciers produced a complex morpho-sedimentary record. While the reconstructed LGM ice extent is laterally constant in the west, it shows significant variations in the central and eastern parts. We explore how these geological differences relate to local climatic variability and global paleoclimate during a period of rapid climate change in the late Pleistocene.

In this study, we employ cosmogenic ³⁶Cl in limestone to constrain the in-situ exposure age of glacial erratics situated on moraine walls of the Iller Piedmont Glacier. We sampled erratic boulders from three moraine crests previously interpreted to represent the LGM and two post-LGM retreat stands. We measured ³⁶Cl/Cl and Cl-nat of seven samples from all three locations by applying routine chemistry protocols (Merchel et al., 2013) and isotope-dilution AMS measurements using a dedicated ion source for halogenides (Pavetich et al., 2014) at the DREsden AMS facility.

Preliminary results show that the sampled boulder surfaces provide internally consistent, reproducible, and geologically meaningful dates. Field investigations indicate that some of the erratic boulders were affected by chemical weathering, slope processes or human activities after their glacial deposition, thereby influencing the measured in-situ ³⁶Cl concentrations. In order to account for these complexities, we apply appropriate correction factors to obtain more accurate ages and discuss the related uncertainties.

Sample preparation of 14 additional samples was performed at the Laboratory for cosmogenic nuclide extraction at the University of Natural Resources and Life Sciences (BOKU) in Vienna. We will likely present ³⁶Cl/Cl and Cl-nat data of these additional samples measured at the Vienna Environmental Research Accelerator (VERA) at the time of the meeting. The exposure age data elucidate the spatio-temporal patterns of receding glaciers in the Northern Alpine Foreland, and place constraints on climate reconstructions for Central Europe during the late Pleistocene.

Acknowledgements:
We are grateful to Stephanie Neuhuber (BOKU Vienna) for providing access to her CN laboratory. Kathrin Strößner, Hagen Hoemann, Paul Herwegh, Kaja Schulz and Sami Akber (all LMU Munich) are thanked for assistance with sample preparation. This work was funded by DFG (German Science Foundation) grant FR 1673/15-1. Parts of this research were carried out at the Ion Beam Centre (IBC) at the Helmholtz-Zentrum Dresden–Rossendorf (HZDR) e. V., a member of the Helmholtz Association, supported by the HZDR Beamtime Proposal 20002195-ST. AMS measurements and sample preparation in Vienna are supported by the RADIATE project under the Grant Agreement 824096319 from the EU Research and Innovation programme HORIZON 2020 trough the Transnational Access grant 21002431-ST.

References:
Merchel et al., Quat. Geochron. 18 (2013) 54.
Pavetich et al., NIMB 329 (2014) 22.


Biography:

Dominic is a graduate student in Earth Sciences at ETH Zurich. He completed his Bachelor’s degree in Geosciences at the LMU and TU Munich with a Bachelor thesis on the paleoenvironmental analysis of Holocene freshwater carbonates, using 14C dating among other methods. He is interested in applying AMS measurements to quantitatively reconstruct past environmental and climate changes.

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Date

Nov 08 - 19 2021