Meteoric 10Be dating of highly weathered soils from fluvial terraces in Taiwan

Abstract: Stream terraces are geomorphic markers that can be used to gauge surface deformation in response to tectonic uplift. The surface deposits of the terraces form a chronosequence that indicates the rate and process of soil development. Placing a time or age constraint upon soil development has become one of the most important factors in the disciplines of soil science and fluvial geomorphology. The radiocarbon (14C) method is unable to date old terraces or soils, but the longer half-life of cosmogenic beryllium-10 (10Be) permits this isotope to be useful to determine soil ages and rates of formation. Red soils (redder than 7.5YR) are commonly distributed on old, high altitude stream terraces throughout Taiwan. In this study, three pedons of alluvium-related red soils were sampled from the Taoyang (TY-YM), Pakua (PK-1), and Chiayi terraces (CY-1), respectively located in northern, central, and southern Taiwan. According to field morphology and chemical analyses, these red soils are characterized in Soil Taxonomy as being highly weathered, and they are classified as Typic Hapludox (TY-YM and PK-1), and Typic Paleudult (CY-1). Meteoric 10Be dating shows ages of ⩾261ka for TY-YM, ⩾124ka for PK-1, and ⩾386ka for CY-1. However, the trend of these ages does not agree with the degree of soil development. The former two ages are likely underestimated through loss of 10Be due to strong leaching and considerable erosion. The age obtained from CY-1 may represent the required time for soils develop into oxisols in Taiwan. [Copyright &y& Elsevier]