Late Quaternary aeolian deposits in the southeastern Mu Us Sandy Land: Insights into the provenance of Asian dust and interpretation of dust records

Abstract

Chinese loess deposits are one of the most important terrestrial archives for understanding past climate change and global atmospheric circulation. However, the nature of loess deposition and the processes involved in it are not fully understood, limiting interpretations of the environmental significance of proxies applied to both loess deposits and distal dust records. On the basis of changes in lithostratigraphy and multiple proxies (grain size, magnetic susceptibility and weight loss-on-ignition), we investigated two outcropped sections in the transitional zone between the Mu Us Sandy Land (MUSL) and the Chinese Loess Plateau (CLP), attempting to depict the nature of aeolian deposition along the desert margins adjacent to the CLP and understand the dust dynamics that potentially affect typical loess deposition and long-range dust deposition from source areas to distal regions. The strata are mainly composed of alternating layers of loess, paleosol and aeolian sand, with obvious unconformities and abrupt grain size changes occurring at the transitions from loess/paleosol to sand deposition. The sand deposits interbedded with typical loess and/or paleosol suggest that proximal deserts have episodically expanded close to the study sites. Based on 15 luminescence dates, a comparison with other well-dated loess sections reveals the absence of strata in section Baijie between 132.5 and 105.7 ka may have resulted from aeolian erosion of previously deposited loess and paleosol during the late Marine Isotope Stage (MIS) 6 and MIS 5e. This erosion was most likely caused by an expansion of the MUSL during MIS 5d, as suggested by a well-sorted sand layer immediately overlying the loess deposition of MIS 6. The loess and/or paleosols previously deposited in upwind regions of the CLP have been partially eroded by winds, acting as a significant source for dust deposits downwind and resulting in dust flux peaks observed in distal marine sediments during MIS 5d. Such a linkage suggests the areas, which had belonged to the CLP and covered by typical loess but at present became a part of the MUSL, could serve as an additional source for dust deposition in the North Pacific during some intervals of the Quaternary. Our results provide insights into dust provenances for proximal Chinese loess and distal marine dust deposition, offering plausible interpretations on existing discrepancies of dust fluxes from different geological archives.