Implication of boron isotope geochemistry for the pedogenic environments in loess and paleosol sequences of central China

摘要

We investigated the boron isotopic composition in loess-paleosol sequences in five different profiles in the Chinese Loess Plateau. Three possible boron sources are identified: atmospheric input, carbonates, and weathered silicate rocks. Variations of [Sr], [B], delta B-11 and the magnetic susceptibility correlate well with the pedogenetic intensity in three out of the five studied profiles, where pedogenesis under a cold-dry climate indicates lower delta B-11, lower [B], lower magnetic susceptibility and higher [Sr] values. Exceptions to the variations between the delta B-11 and other known proxies were observed in arenaceous soils and the Red Clay sequence: the former suggested that vertical redistribution probably occurred with the boron migration, and the latter indicated an unknown mechanism of susceptibility enhancement. A better correlation between the delta B-11 and magnetic susceptibility and the quantitative estimation of boron budget from each source confirms the influence of paleoenvironmental changes on boron geochemical cycle. Significant positive correlations in Sr/Ca vs. B/Ca and Mg/Ca vs. B/Ca reflect consistent enrichment behavior of those mobile elements into calcium carbonate. The preliminary results imply that boron isotopic compositions in soils can be a potential geochemical proxy to reconstruct the paleoenvironmental changes in loess-paleosol sequences. (C) 2014 University of Washington. Published by Elsevier Inc. All rights reserved.