Magnetic and geochemical data

Based on the above magnetic parameters, the ratio parameters χARM/χ, χARM/SIRM, and SIRM/χ were calculated. Furthermore, the S-ratio and hard isothermal remanent magnetization (HIRM) were calculated using the ratio of SIRM to IRM−300mT.Geochemical analyses were conducted at the State Key Laboratory of Ecological Security and Sustainable Development in Arid Regions. The concentrations of heavy metals (Cr, Ni, As, Zn, Pb, and Fe) in soil samples were determined using inductively coupled plasma mass spectrometry (ICP-MS, 8800, Agilent Technologies, USA).

The soil samples were naturally air-dried, cleared of debris, ground, and passed through a 100-mesh nylon sieve prior to analysis. Approximately 0.1000 g of each soil sample was weighed into a polytetrafluoroethylene (PTFE) digestion vessel, to which a mixed acid system of HNO₃–HF–HClO₄ was added. The vessel was then placed in a closed microwave digestion system and subjected to a programmed temperature digestion procedure.

After the digestion solution was evaporated to near dryness and cooled, the residue was diluted to 50 mL with ultrapure water, thoroughly mixed, and kept for subsequent measurement.