Study on Magnetic Characteristics and Variation Mechanisms of Sediments in the Bawang River in the Northern Foothills of Qinling Mountains

Key words: 
• the Northern Foothills of Qinling Mountains /
• river sediments /
• environmental magnetism /
• diagenesis

Abstract: Abstract:[Objective]The northern foothills of the Qinling Mountains lie in the transitional zone between China's northern and southern geomorphological units, serving as a critical link between the Loess Plateau and the Qinling orogenic belt. Conducting research on magnetic characteristics of river sediments in this region holds significant scientific value and theoretical implications for understanding regional environmental evolution processes, sedimentary response mechanisms, and exploring basin-wide environmental change patterns. [Methods]This study focused on the floodplain sediment profile of the lower Ba Wang River in the northern Qinling foothills. Through systematic environmental magnetism analysis combined with principal component analysis (PCA), we investigated magnetic characteristics and dominant mechanisms across different sedimentary stages. [Results]The sedimentary profile exhibited distinct differentiation at the 124cm depth marker, with generally weak magnetic properties. In the lower section of Stage I (308-124 cm), the sediments exhibit relatively weak magnetism, with magnetic minerals primarily consisting of hematite and siderite, along with minor magnetite, with magnetic particle sizes gradually coarsening into multi-domain (MD) particles. Stage Ⅱ (124-24cm) sediments showed significantly enhanced magnetism, primarily consisting of small sized pseudo-single domain (PSD) magnetite and magnetite, alongside minor hematite content. PCA results further confirmed stratification features: the cumulative contribution rate of two principal components ferromagnetic mineral content and magnetic particle size reached 89%. Variations in magnetite content within ferromagnetic minerals were the dominant factor explaining magnetic differences across sedimentary stages. [Conclusion]Stage I sediments remained submerged in a reducing environment for prolonged periods, leading to dissolution of magnetite under early diagenetic processes. Stage Ⅱ sediments, exposed to an oxidizing environment, exhibited magnetic characteristics shaped by hydrodynamic sorting and weak soil-forming processes. This study enhances our understanding of factors influencing sediment diagenesis, providing crucial reference materials for analyzing the characteristics of sedimentary environment changes and climatic environmental variations in the Wei River Basin.