罗布泊盐湖沉积物磁性特征及其环境意义

Magnetic properties of Lop Nur saline sediments and the environmental implications

以罗布泊盐湖沉积物为研究对象,以环境磁学为主要研究方法,探讨罗布泊盐湖沉积物磁性特征的影响因素和环境意义。根据磁性特征可将罗布泊LOP1剖面沉积物分为两类:磁铁矿主导和铁硫化物(胶黄铁矿和黄铁矿)主导。磁铁矿主要来源于物源区塔里木盆地。胶黄铁矿和黄铁矿是早期还原成岩作用的产物,对磁性特征产生显著影响,胶黄铁矿主导层具有明显较高的χ、SIRM、χARM、χARM/χ和S-300 mT,黄铁矿相反。有机质供应增加是罗布泊盐湖沉积早期成岩作用的触发因素,中晚全新世以来冷事件期间塔里木盆地湿度改善,有机质供应增加,促使了早期成岩成因的自生铁硫化物生成。

This article presents the particle size,total organic matter,rock magnetic,and x-ray diffraction analyses of saline lake sediments,aeolian sands,Tramarix cone,and yardangs sediments distributed along the west bank of Lop Nur.The aim was to investigate the vertical variations and influencing factors of magnetic characteristics,as well as the paleoenvironmental implications.Based on the magnetic properties,Lop Nur sediments can be divided into two types.In oxidizing environments,sediment magnetic properties are dominated by magnetite,which is consistent with the source materials(Tarim Basin)and are unaffected by early diagenesis.In reducing environments,sediment magnetic properties are dominated by authigenic iron sulfide(greigite and pyrite),which formed in the early diagenesis process.Layers that are dominated by greigite or pyrite have markedly higher or lowerχ,SIRM,χARM,andχARM/χand S-300 mT,respectively,reflect the significant impact of early diagenesis on magnetic properties in the Lop Nur.Combined with the results of chronology from a previous study,we determined that the iron sulfide-bearing sediments were deposited during cold and wet periods,which were probably caused by the North Atlantic cold events that occurred throughout the past 3400 yr.During these periods,iron sulfide formation was likely driven by an enhanced organic matter supply.The magnetic parameters of Lop Nur sediments can be regarded as an indicator of the hydrological and climatic evolution of the Tarim Basin.