Geochemical Journal, Vol. 44 (No. 6), pp. e23-e27, 2010EXPRESS LETTER
Kazuyo Shiroya,1,2 Yusuke Yokoyama1,2 and Hiroyuki Matsuzaki3
1Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8504, Japan
2Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
3Department of Nuclear Engineering and Management, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
(Received October 8, 2010; Accepted November 26, 2010; Online published December 8, 2010)
We present erosion rates of granitic soil surfaces in the western Abukuma upland, Japan using depth profiles of in-situ produced cosmogenic 10Be and 26Al based on physical parameters for both neutron and muon interactions. Samples were obtained below the severely weathered zone, from 30 to 190 cm depth below surface (bs). We confirmed that, in this environment, deeper layers from at least 80 cm bs must be analyzed to achieve highly accurate measurement of erosion rate because near-surface layers are potentially influenced by pedogenic processes. The depth profiles obtained suggest a surface-lowering rate of 49-74 m/Myr for a mountain ridge composed of granitic soil. This newly obtained erosion rate is much higher than previously reported granitic or metamorphic bedrock, as well as quartz vein, erosion rates from several climatic environments including humid regions, suggesting that granitic soil surface is more susceptible to erosion.
Key words: weathered granitic soil surface, erosion rate, cosmogenic 10Be and 26Al, depth profile, sampling depth