10Be inventories in Alpine soils and their potential for dating land surfaces

Abstract

To exploit natural sedimentary archives and geomorphic landforms it is necessary to date them first. Landscape evolution of Alpine areas is often strongly related to the activities of glaciers in the Pleistocene and Holocene. At sites where no organic matter for radiocarbon dating exists and where suitable boulders for surface exposure dating (using in situ produced cosmogenic nuclides) are absent, dating of soils could give information about the timing of landscape evolution. This paper explores the applicability of soil dating using the inventory of meteoric 10Be in Alpine soils. For this purpose, a set of 6 soil profiles in the Swiss and Italian Alps was investigated. The surface at these sites had already been dated (using the radiocarbon technique or the surface exposure determination using in situ produced 10Be). Consequently, a direct comparison of the ages of the soils using meteoric 10Be and other dating techniques was made possible. The estimation of 10Be deposition rates is subject to severe limitations and strongly influences the obtained results. We tested three scenarios using a) the meteoric 10Be deposition rates as a function of the annual precipitation rate, b) a constant 10Be input for the Central Alps, and c) as b) but assuming a pre-exposure of the parent material. The obtained ages that are based on the 10Be inventory in soils and on scenario a) for the 10Be input agreed reasonably well with the age using surface exposure or radiocarbon dating. The ages obtained from soils using scenario b) produced ages that were mostly too old whereas the approach using scenario c) seemed to yield better results than scenario b). Erosion calculations can, in theory, be performed using the 10Be inventory and 10Be deposition rates. An erosion estimation was possible using scenario a) and c), but not using b). The calculated erosion rates using these scenarios seemed to be plausible with values in the range of 0-57â mm/ky. The dating of soils using 10Be has several potential error sources. Analytical errors as well as errors from other parameters such as bulk soil density and soil skeleton content have to be taken into account. The error range was from 8 up to 21. Furthermore, uncertainties in estimating 10Be deposition rates substantially influence the calculated ages. Relative age estimates and, under optimal conditions, absolute dating can be carried out. Age determination of Alpine soils using 10Be gives another possibility to date surfaces when other methods fail or are not possible at all. It is, however, not straightforward, quite laborious and may consequently have some distinct limitations.

Soil formation rates on silicate parent material in alpine environments: Different approaches–different results?

“…However, very high production rates are also observed in areas with no or very low erosion ( Fig. 3; Egli et al, 2010a). The compilation presented here shows that the highest production rates are on the youngest surfaces.…”

“…For this approach, erosion effects on stable landscape positions are considered as nearly negligible (see e.g. Egli et al, 2010a;, so that soil and vegetation cover and/or a favourable topographic position drastically reduce erosion. Calculation of the time elapsed since conversion from bedrock to soil in each horizon of a weathering profile.…”

Meteoric 10Be in soil profiles – A global meta-analysis

“…Maejima et al, 2005). In the 22 meteoric 10 Be profiles where distinct A, B, and C soil horizons were identified (Pavich et al, 1984(Pavich et al, , 1986Pavich and Vidic, 1993;Barg et al, 1997;Stanford et al, 2000;Harden et al, 2002;Maejima et al, 2004;Shen et al, 2004a;Egli et al, 2010), the full range of values is found in both A and B soil horizons, with an average of 4.5 Â 10 8 atoms/g (Electronic Annex). C horizons have significantly less meteoric 10 Be.…”

Cosmogenic 10Be as a potential dating tool in peat

“…Inventories of 10 Be in mineral soils have been used as the basis for dating over thousands of years (e.g., Egli et al 2010;Willenbring and von Blanckenburg 2010). In these applications, the 10 Be deposition rate must be either measured or more commonly estimated through models, and corrections must be made for the in situ cosmogenic production of 10 Be in quartz minerals in soil, losses of 10 Be from the soil via erosion, and radioactive decay of 10 Be.…”