EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Delving deeper into cosmogenic 26Al-10Be isochron-burial dating of Swiss Deckenschotter deposits

Ewelina Broś1, Florian Kober2, Susan Ivy-Ochs1, Reto Grischott3, Marcus Christl1, Christof Vockenhuber1, Colin Maden4, and Hans-Arno Synal1
Ewelina Broś et al.
  • 1Laboratory for Ion Beam Physics, ETH Zurich, Otto-Stern Weg 5, 8093 Zürich, Switzerland
  • 2NAGRA, Hardstrasse 73, 5430 Wettingen, Switzerland
  • 3Büro für Technische Geologie BTG AG, Grossfeldstrasse 74, 7320 Sargans, Switzerland
  • 4Department of Earth Sciences, ETH Zurich Sonneggstrasse 5, 8092 Zürich, Switzerland

The oldest Quaternary deposits of the Swiss Northern Alpine Foreland are found on numerous hilltops, up to 300 m above the current valley bottoms. These Deckenschotter deposits consist mainly of glaciofluvial sediments intercalated with glacial sediments. Traditionally, the Deckenschotter are divided into two units: Höhere Deckenschotter (HDS – Higher Deckenschotter) and Tiefere Deckenschotter (TDS – Lower Deckenschotter). Elevation differences between the two suggest a phase of 100-150 m of incision (Graf, 2009).

Knowledge of their age of deposition is necessary for understanding the long-term landscape evolution as well as for assessing the long-term safety of the planned deep geological repository for nuclear waste in northern Switzerland (NTB 14-01, 2014). In this study, the method of isochron-burial dating was implemented to address the question of the age of the Deckenschotter. We aim to reconstruct the chronology of the alternating deposition and incision of the gravel units in the Northern Alpine Foreland. Our focus is placed on similar and complementary Deckenschotter sites located in the Northern Alpine Foreland in crucial locations in order to establish sound long-term landscape evolution scenarios. One of these is a former gravel pit, Feusi, situated in the southern slope of the hill chain called ‘Egg’ or ‘Schliniker Platten’, north of the village Oberweningen. The outcrop comprises several gravel units intercalated with glacigenic diamict layer in the upper part. Previous age estimates with the isochron-burial dating method indicate an age of 1.1 ± 0.2 Ma for the diamict layer (NAB 19-025, 2020). Knudsen et al. (2020) reported an age of 0.93 ± 0.13 Ma for the same layer based on a slightly different age calculation approach.

We sampled the lowermost accessible horizon, the Egg Schotter, of the Feusi outcrop at an altitude of ~580 m a.s.l. This horizon is located close to the base of the outcrop, just a few meters above the contact with the underlying Molasse and in a clear stratigraphic position, 20 m below the previously dated diamict. Study of the lowermost unit will allow us to temporally examine the earliest phases of Deckenschotter accumulation. Weathering horizons in the gravel layers overlying the Egg Schotter suggests periodic subaerial exposure. Therefore, the total time contained in the sediment package is difficult to estimate. Having two horizons dated at different depth in the same outcrop may provide insight into the timespan hidden between the deposition and weathering of different gravel layers. Indications of the timespan of HDS activity could be further gleaned by comparing to the age from the glacigenic sediment. In order to achieve this, eight clast samples of quartz-rich lithologies, of various shapes and sizes were collected in the Egg Schotter and processed for isochron-burial dating. The cosmogenic nuclides 10Be and 26Al were extracted and measured with the new MILEA accelerator at the accelerator mass spectrometry facility, ETH Zurich. The first results of this study will be presented.


Graf, H.R. 2009: Quaternary Science Journal 58, 12–53

Nagra, NTB 14-01, 2014

Nagra, NAB 19-025, 2020

Knudsen, M.F. et al. 2020. Earth and Planetary Science Letters, 549, 116491

How to cite: Broś, E., Kober, F., Ivy-Ochs, S., Grischott, R., Christl, M., Vockenhuber, C., Maden, C., and Synal, H.-A.: Delving deeper into cosmogenic 26Al-10Be isochron-burial dating of Swiss Deckenschotter deposits, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12374,, 2021.

This abstract will not be presented.