Genesis of Loess Particles on the Chinese Loess Plateau

Abstract

The sources of the sediments in distinct areas of the Chinese Loess Plateau (CLP) are still disputed, starting with the particle formation in the original desert areas, as well as the neighboring river systems. The formation of loess particles in the southern CLP was investigated using Scanning Electron Microscopy (SEM) and combined material modal composite analysis. Here, we determined the mineralogy in the Duanjiapo (DJP) section on the southernmost CLP and the last glacial‐interglacial samples on the central and north CLP. The results reveal that the samples plot along the N‐S transect, which is very likely the result of differential weathering. The SEM observations of the internal textures of soil aggregates from DJP suggest that precipitation mediated dissolution led to the formation of the fine particle fraction (5–10 μm). The most dissolution was observed for the hornblende particles. The further evolution of these smaller particles followed a decrease (2.6–0 Ma) in the grain size up section. Our record of the changes in and trend of the hornblende concentrations suggests an imbalance in the budget of the hornblende influx via sub‐aerosol wind transport versus the mineral dissolution, which provides robust evidence for a sediment provenance in the deserts north and west of CLP. Understanding the sediment source is critical to trace Asian monsoon evolution. The hornblende record suggests a coeval change in the trends of the summer monsoon and winter monsoon, and this contemporaneous change may not support the recently proposed Pacific Walker Circulation mechanism in the interpretation of Asian monsoon.

A hybrid mechanism for the initiation and expansion of loess caves across the Chinese Loess Plateau

“…Vegetation cover also increases in the same direction (Wang et al, 2018), gradually transitioning from grassland to forest (Feng et al, 2013). Loess particles are transported from the northwestern Gobi Desert and sand desert by wind and are being accumulated in the CLP since the beginning of the Quaternary (Zhu et al, 2022). The particle size becomes finer and loess thickness decreases from northwest to southeast, that is, with increasing distance from the sand sources (Maher, 2016).…”