Meteoric Be-10, clay, and extractable iron depth profiles in the Colorado Front Range: Implications for understanding soil mixing and erosion

摘要

Analyzing meteoric Be-10 in soil profiles along with soil measurements such as pedogenic Fe and clay content permits better understanding of meteoric Be-10 transport in soils, soil formation, and hillslope geomorphology. This study presents meteoric Be-10 depth profiles from saprolite-derived soil catenas sampled in the Gordon Gulch catchment, Colorado Front Range and from nearby c. 130 and 15 ka glacial moraines. We compare meteoric Be-10 data with more classically used soil analyses of clay and extractable iron (Fed) content. Meteoric Be-10 and Fed do not show consistent trends in the hillslope profiles. Meteoric Be-10 and clay concentrations, however, generally decrease with depth and highest concentrations of Be-10 in horizons coincide with highest clay concentrations. Soils at moraine sites are better developed than those on hillslopes, and correlations of Be-10, Fed, and clay are stronger. In Gordon Gulch, south-facing hillslopes display meteoric Be-10 bulges at depth and lower near-surface concentrations compared to the declining profiles and higher near-surface concentrations of north-facing hillslopes. The aspect differences imply that south-facing hillslopes experience greater vertical mixing than north-facing hillslopes, and that greater lateral transport and erosion has occurred over the last 15-20 ka on south-facing hillslopes relative to north-facing hillslopes. Meteoric Be-10 depth profiles at moraine sites display bulge profiles with highest meteoric Be-10 concentrations in B-horizons, reflecting landform stability and pedogenic processes. Overall, our data demonstrate that signatures of chemical weathering in soils (Fed and clay) may or may not correlate to the meteoric Be-10 added through atmospheric deposition, and that profile shape of meteoric Be-10 can provide insight into the relative contribution of vertical mixing and surface erosion in relation to catena location and aspect during hillslope evolution. (C) 2014 Elsevier B.V. All rights reserved.