Characteristics Of Iron Mineralogy In The Loess Of The Eastern Tibetan Plateau And Their Paleoenvironmental Significance

The eastern Tibetan Plateau（ETP）is primarily affected by the Indian monsoon,plateau monsoon,and westerly circulation.Its widely dispersed loess deposits are one of the good and continuous geological carriers in the plateau area,providing an ideal window into the changes in the environment of Tibetan Plateau（TP）and its environmental effects of TP since the Pleistocene,as well as the evolution and interaction of various elements of the Asian monsoon system.The environmental magnetism-based ferromagnetic mineral record of the loess plateau is crucial in revealing the evolution and driving mechanism of the East Asian monsoon.This research reveals the magnetic characteristics and spectral characteristics of ferromagnetic minerals of loess in the ETP,as well as the magnetic change mechanism,through systematic environmental magnetic and spectral analysis of the Ganzi（XS）section,Markang（MK）section,and Zhouqu（ZQ）section.The paper thoroughly discusses the indicative significance of magnetic parameters and spectral parameters to environmental change,revealing the history and possible driving mechanism of climate change in the plateau since the last interglacial period.The following are the main conclusions:（1）The magnetic mineral composition of loess in the ETP is similar to the Chinese Loess Plateau（CLP）,with low coercivity ferromagnetic minerals such as magnetite and maghemite,while antiferromagnetic minerals such as hematite and goethite predominate.The fine-grained magnetic minerals formed during the soil-formation process are primarily concentrated in the clay components.Loess contains three magnetic coercivity components that correspond to different types of magnetic minerals.The magnetite/maghemite concentration in the paleosol layer is high with the fine magnetic particle size,whereas the concentration in the loess layer is low with the coarse magnetic particle size.The magnetic particle size of MK and XS loess are primarily composed of relatively coarse stable single domain（SSD）and superparamagnetic（SP）particles,whereas the ZQ section are primarily composed of pseudo single domain（PSD）and multidomain（MD）particles.（2）The magnetism of loess in the ETP is influenced by dust properties and the regional soil-forming environment.Because of the significant differences in landscape and environment between the glacial and interglacial periods on the TP,the magnetic minerals carried by dust differ;the contribution of primary clastic magnetic minerals in interglacial dust to magnetic susceptibility is lower,while that of primary clastic magnetic minerals in glacial dust is higher.The silt component’s deposition hematite concentration has a significant contribution to the change in HIRM,whereas the clay component has a limited contribution to HIRM.The magnetite and magnetite concentrations of SP and SD produced during the pedogenesis are the primary reason for the enhancement of magnetism.However,the regional soil-forming environment may lead to the easier conversion of ferrous magnetic minerals into antiferromagnetic minerals,resulting in a lower concentration of ferrous magnetic minerals in the loess.（3）The magnetic parameters of loess in the ETP are primarily used to indicate precipitation changes.Precipitation and temperature configuration may restrict the oxidation-reduction degree to controlling the concentration combination of weakly magnetic minerals and ferromagnetic minerals in different regions.The production of ferromagnetic minerals is mainly controlled by the temperature changes during the low temperatures condition.The hematite concentration in the loess layer is low,and the hematite concentration in the paleosol is relatively high.The second derivative curve shape of the diffuse reflectance spectrum is basically consistent,showing obvious characteristic valleys of hematite and goethite.The variation of goethite in loess in different regions is relatively complex.The index of magnetic particle size has varying sensitivity to changes in precipitation.The dust difference between interglacial and glacial periods has affected magnetic susceptibility,and magnetic susceptibility cannot clearly indicate precipitation change.X_fd andX_ARM are primarily used to indicate the concentration of fine-grained magnetite,and maghemite produced during the pedogenesis,and can be used as a good substitute precipitation indicator.（4）The ETP experienced the most precipitation and the highest temperature during MIS 5 and MIS 1,while these conditions were less favorable during MIS 4 and MIS 2.Early in MIS 3,temperatures and precipitation were both relatively low,but by the middle of the period,temperatures had risen significantly;and by the end of the period,precipitation had peaked in a warm and muggy environment.The temperature change from the Interglacial to the Glacial in the interior dust source of TP is the same as on the ETP.Temperature and precipitation fluctuations during MIS 3 were likewise characterized by a high frequency and amplitude.On the glacial-interglacial scale,the evolution of temperature and precipitation in the TP since MIS 5 was mainly controlled by the Earth’s orbit parameter of eccentricity,obliquity and precession.And the changes in ice volume may have significant impacts on the climate evolution of the TP.The millennium-scale changes superimposed on the orbital-scale changes in the ETP,reveal the profound impact of the high-latitude climate system in the northern Hemisphere.