A new method for the rapid identification of accretionary and non-accretionary paleosols: Insights from loess deposits in monsoonal China

Identifying accretionary and non-accretionary paleosols is essential for deciphering the paleoclimatic and paleoenvironmental records of loess-paleosol sequences. However, relatively little research has been conducted on the identification, either because the available methods are time-consuming, highly specialized, and expensive, or because they require knowledge of glacial-interglacial patterns of wind dynamics which may still be lacking. The available identification methods are based on dust deposition; however, in this study, we develop a rapid identification method based on pedogenesis by utilizing loess deposits on the Chinese Loess Plateau (CLP) and the Xiashu loess deposits, both of which are in monsoonal China. Firstly, we identified non-accretionary paleosols in a typical Xiashu loess section from the perspective of dust deposition, using SiO2/Al2O3 and SiO2/TiO2 ratios, which are indicators of changes in the detrital eolian grain size. Then, we conducted a comparative analysis of a typical CLP accretionary paleosol-loess couplet and the Xiashu non-accretionary paleosol-loess couplets, using records of magnetic susceptibility (MS), chemical index of alteration (CIA), and grain size. The results show that the accretionary paleosol-loess couplet is characterized by an in-phase relationship between MS and CIA/<2 μm (%), whereas the non-accretionary paleosol-loess couplet has an out-of-phase relationship. The determination of the phase relationship between MS and CIA/<2 μm (%) is a new method that enables the rapid and direct identification of accretionary and non-accretionary paleosols.