Paleosols identified by rock magnetic properties indicate dam-outburst events of the Min River, eastern Tibetan Plateau

Abstract

River terrace sediments are archives of past fluvial processes and they may also reflect a wide range of additional environmental processes. Detailed studies of river terrace sediments are important for understanding the role of tectonics, climate and extreme geomorphological events in fluvial evolution. Here, we present a sedimentary reconstruction using the combination of field description, magnetic measurements and optically stimulated luminescence and AMS 14C dating of the Maoxian (MX) section in the third terrace of the Min river, in the eastern margin of the Tibetan Plateau. The section is mainly composed of clastic deposits and spans the interval from the last glacial to late Holocene. Apart from the silt at the bottom and the gravel layer in the middle, it is difficult to determine whether other clastic deposits were exposed sub-aerially. Multiple magnetic proxies indicate that the MX section contains three layers of pedogenic production of fine-grained magnetite/maghemite, which correspond to paleosol layers. The paleosol layers indicate the occurrence of at least three intervals of exposure to the atmosphere. The three paleosol layers were likely caused by dam-outburst events. The results demonstrate that rock magnetic methods are a useful approach for identifying paleosol layers in fluvial sediments.