Pedogenesis controls magnetic enhancement in the western Sichuan Plateau: Evidence from magnetic properties of particle-sized samples in Jinchuan loess

Abstract

The provenance, transportation patterns, and magnetic enhancement mechanisms of the loess-paleosol sequences in the Western Sichuan Plateau (WSP) remain uncertain, hindering further exploration of the climatic information recorded in the WSP loess and its potential response to global climate change. This study aimed to uncover these issues by integrating the Sr-Nd-Hf isotope compositions, particle size distribution curves, and magnetic properties of particle-size fractions. The results indicated that detrital materials from the northern/interior Tibetan Plateau (TP) and sources nearby, transported by low-level winds and TP winter monsoons, may constitute a potential provenance for WSP loess. An increase in superparamagnetic (SP) magnetite/maghemite within finer particles enhanced the magnetic properties throughout pedogenesis. A distinct particle boundary emerged at 4–8 µm, where the susceptibility (χlf) loss in coarser fractions (>8 µm) in loess was roughly equal to the χlf increase (13.43 %) in finer particles (<4 µm) in paleosols. Approximately 69 % of the χlf increase could be attributed to SP mineral grains. The final products of pedogenesis, hematite and goethite, exhibited a significant increase in the < 1 µm fraction, emphasizing their role in indicating pedogenesis and providing magnetic mineral transformation.