&amp;lt;sup&amp;gt;10&amp;lt;/sup&amp;gt;Be depth profiles in glacial sediments on the Swiss Plateau: deposition age, denudation and (pseudo-) inheritance

Lorenz Wüthrich,Marcus Christl,Régis Braucher,Roland Zech,Heinz Veit,Carla Terrizzano,Christian Gnägi,Claudio Brändli,Negar Haghipour

doi:10.5194/egqsj-66-57-2017

Abstract

Abstract. During the Pleistocene, glaciers advanced repeatedly from the Alps onto the Swiss Plateau. Numeric age control for the last glaciation is good and thus the area is well suited to test a method which has so far not been applied to till in Switzerland. In this study, we apply in situ produced cosmogenic 10Be depth profile dating to several till deposits. Three sites lie inside the assumed Last Glacial Maximum (LGM) extent of the Rhône and Aare glaciers (Bern, Deisswil, Steinhof) and two lie outside (Niederbuchsiten, St. Urban). All sites are strongly affected by denudation, and all sites have reached steady state, i.e., the 10Be production is in equilibrium with radioactive decay and denudational losses. Deposition ages can therefore not be well constrained. Assuming constant denudation rates of 5 cm kyr−1, total denudation on the order of 100 cm for sites within the extent of the LGM and up to tens of meters for older moraines are calculated. Denudation events, for example related to periglacial conditions during the LGM, mitigate the need to invoke such massive denudation and could help to explain high 10Be concentrations at great depths, which we here dub pseudo-inheritance. This term should be used to distinguish conceptionally from true inheritance, i.e., high concentrations derived from the catchment.

Highlights

In 1909, Albrecht Penck and Eduard Brückner published their famous and seminal three-volume work Die Alpen im Eiszeitalter (Penck and Brückner, 1909)
Our study aims to i. evaluate the potential of 10Be depth profile dating of moraines, ii. investigate denudation rates and total denudation, and iii. quantify inheritance
The steady-state denudation rate between the first and second sample does not increase with depth

Summary

Introduction

In 1909, Albrecht Penck and Eduard Brückner published their famous and seminal three-volume work Die Alpen im Eiszeitalter (Penck and Brückner, 1909). They proposed four ice ages during the Quaternary: Würm, Riss, Mindel and Günz. It was proposed that Alpine glaciers advanced at least 15 times onto the Swiss Plateau (Schlüchter, 2010; Preusser et al, 2011). New nomenclature was introduced for the Swiss glaciations (Graf, 2009; Preusser et al, 2011; Keller and Krayss, 2011). Würm is called Birrfeld Glaciation and encompasses marine isotope stages (MIS) 5d to 2, the penultimate glacial was renamed from Riss to Beringen and probably occurred during MIS 6 (Ivy-Ochs et al, 2006b; Graf et al, 2007, 2015), and the most extensive glaciation is referred to as Möhlin Glaciation (> 300 ka; Graf, 2009; Preusser et al, 2011)

Methods

Results

Conclusion