Differentiating detrital and pedogenic contributions to the magnetic properties of aeolian deposits in the southern Tibetan Plateau: Implications for paleoclimatic reconstruction

Abstract

Aeolian deposits in the Yarlung Zangbo River (YZR) valley in the southern Tibetan Plateau (TP) have recorded the evolution of past climate and atmospheric circulation in the “Asian water tower” region. However, the paleoclimatic history of the region remains controversial, largely because of ambiguous proxy environmental indicators. Here, we conducted the first detailed investigation of the environmental magnetic properties of two Holocene aeolian sedimentary sequences in the valley. Combined with geochemical and sediment granulometry data, we clarify the magnetic enhancement mechanisms and the paleoclimatic implications of the magnetic parameters. The results reveal spatial differences in magnetic properties, which makes sense in relation to the climatic gradient in this region. Due to the stronger Indian summer monsoon (ISM), ferrimagnetic and imperfect antiferromagnetic minerals (both coarse and fine-grained) dominate the sedimentary magnetic properties in the middle reaches of the YZR, suggesting both detrital and pedogenic origins. Hence, although both wind activity and pedogenesis cause the observed magnetic enhancement, magnetic parameters sensitive to the presence of fine magnetic grains can be used as paleo-moisture and/or temperature proxies. With decreasing ISM precipitation, the sedimentary magnetic properties in the upper reaches of the YZR are dominated by coarse ferrimagnetic grains, indicating the dominant influence of detrital input. Hence, the variations in sedimentary magnetic properties are caused by changes in paleo-wind intensity, given the constant material source. Accordingly, we propose a conceptual model that explains the spatiotemporal variations in dust accumulation and magnetic properties in this region. Our results provide a sound basis for understanding the sedimentary magnetic properties and their application in paleoclimatic reconstruction in the southern TP.