Special projects between Bavaria and Georgia

Dr. Markus Fuchs

Lehrstuhl Geomorphologie
Universität Bayreuth

Dr. K. Frankel

School of Earth and Atmospheric Sciences
Georgia Institute of Technology

Combined Dating of Alluvial Fans using SED 10Be and OSL dating techniques

Alluvial fans are valuable and important natural archives to investigate past climate conditions. The knowledge about the paleoclimate is needed to understand how climate evolves over geological times, which helps to understand future climate change. To calibrate and test climate models, paleoclimate information are essential. Using natural archives as paleoclimate proxies it is crucial to know the age of the proxy. For alluvial fans surface exposure dating (SED) with cosmogenic nuclides like10Be is an innovative technique to date alluvial fans. In combination with optical stimulated luminescence (OSL) dating the ages of both techniques can be cross chec

Final report

In total, 17 boulders were sampled for surface exposure dating (SED) using the cosmogenic nuclide 10Be. The boulders came from the surface of an alluvial fan and from one surface of a sediment ridge, situated in the valley of the corresponding alluvial fan. For comparison, additional sediment samples for optical stimulated luminescence dating (OSL) were taking from the same geomorphological features as the 10Be samples. The 10Be samples were prepared and measured at US facilities, the OSL samples were prepared and will be measured in Bayreuth / Germany.

First 10Be results clearly show Holocene ages of the boulders, with probably three distinct accumulation periods. These ages are consistent with the sedimentary and geomorphological results, indicating their correctness. The validation of the 10Be datings with OSL is still in progress, but first test measurements of the equivalent doses show good agreement between both dating techniques. We therefore could show that both techniques are promising to date sediments from the study area in the SW USA, an important step towards the use of these sedimentary archives for paleoclimate reconstruction.

In the future, the US and German laboratories will closely cooperate in the field of SED and OSL dating, to develop new chronologies for the SW USA and to better understand past climate conditions. For 2011, a laboratory and field visit is already projected, and a subsequent research proposal planned.



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