The magnetic properties of Attock loess and its environmental significance in Pakistan

The magnetic susceptibility of the loess-paleosol sequence is considered a significant indicator for recording paleoclimate, and the relationship is different between magnetic susceptibility and climate variation in diverse regions. A deep analysis of the composition, content, and evolution mechanism of magnetic minerals is helpful to enhance our understanding of magnetic signals in different regions. This paper presents a systematic study of environmental magnetism and geochemical elements in the loess-paleosol sequence of the Attock (ATT) area in the Peshawar Basin, northern Pakistan, exploring the significance and limitation of magnetic susceptibility as a proxy index of paleoclimate and the variation mechanism of magnetic susceptibility. The results showed that: 1) the ATT section had a magnetic mineral composition similar to that of the Chinese Loess Plateau; however, the contents of different minerals were distinguishable. The loess layer contained a specific amount of magnetite and maghemite and a handful of goethite and hematite. Additionally, the content of soft magnetic minerals was relatively higher than that of paleosol; the paleosol contained maghemite and nearly no magnetite. Furthermore, it contained more hematite and goethite, and the hard magnetic and paramagnetic minerals were dominant; 2) the effective humidity of the pedogenic environment in the ATT section fluctuated around the magnetic susceptibility wetting critical value F (B–C region), resulting in a poor relationship between magnetic susceptibility and climate; 3) Rb/Sr, K/Na, the coefficient of eluviation, and the content of <2 μm particles were well correlated with the stratum and can be used as paleoclimatic variation indicators in this area. Understanding the B–C region is helpful to comprehend the complex relationship between magnetic signals and climate in some areas and better interpret the environmental information carried by magnetic signals.