Quantitative analysis the provenance of loess in the upper Hanjiang River, China: Evidence from heavy minerals and grain-size

Abstract

Understanding the provenance of aeolian loess is crucial for gaining insights into dust transport processes, atmospheric circulation, and climate change. The loess in the upper Hanjiang River (UHR), situated between the Qinling and Daba Mountains, acts as a natural divide between northern and southern China. Identifying and quantifying the sources of loess in the UHR are essential for elucidating the mechanisms of Asian dust release. This study used grain-size and heavy mineral analysis to determine whether the loess on the UHR's first terrace primarily originates from proximal or distant sources. We quantified the contributions of these sources using advanced techniques such as the Conservativeness Index (CI) and Consensus Ranking (CR). Our findings revealed that the UHR loess was mainly derived from weathered materials from the proximal Qinling-Daba Mountains, accounting for 62 ± 3 %. The weathered materials from the proximal Qinling-Daba Mountains to be stored in the floodplains. Subsequently, they were deposited on the river terraces by the mountain valley winds. The Chinese Loess Plateau, representing the distant-source arid inland in northwest China, contributes 38 ± 3 %, primarily through fine particles that dust storms elevate thousands of meters into the atmosphere, and the East Asian winter monsoon transports across long distances, eventually depositing them into the UHR after crossing the Qinling Mountains. However, the sources of UHR loess varied geographically. The Hanzhong Basin and Yunxian Basin predominantly received materials from proximal sources, whereas the Ankang Basin was primarily supplied by distant source materials. This difference spatial variation in loess provenance is likely to be influenced by a combination of rivers, monsoons, and mountain ranges. In conclusion, unlike the loess of the Chinese Loess Plateau, which predominantly originates from the arid inland region of northwest China, the UHR loess is primarily derived from weathered products of the proximal Qinling Mountains. This study demonstrates that the CI, CR models constitute an effective approach for quantitative provenance research in loess.