Rock Magnetic Properties Of Late Miocene The Fluvio-lacustrine Sediments From The Lanzhou Basin

Lanzhou basin is located in the northeastern margin of Tibetan plateau,is the intersection regionof westerlies and the intersection of east Asian monsoon,and it is the Transition zone of half arid of arid zone.There is a lot of good development in the basin,the late Cenozoic lacustrine facies strata and the presence of large amounts of ancient human sites and mammal fossils,it has important influence in the Quaternary geology.In recent years,through using magnetic stratigraphy,biostratigraphy and comprehensive means of research,it makes our undrerstanding of some of the problems of high basin,such as s framework of fauna.The study of lanzhou basin are mainly concentrated in mammalian fossils and sporopollen fossil plants and research of sedimentology.Since the Quaternary paleoenvironment evolution research is relatively weak.In this paper,In this paper,we use the petrographic method and the environmental magnetism method is studied in Lanzhou basin in the rock magnetism of the Late Miocene sediments,revealed that at the time of the climate types and change of the magnetic properties of mechanism,The paleoclimatic significance revealed by the change of the magnetic properties at high temperature provides some literature support for the rock mechanics work in this area.The following results are obtained:(1)The magnetic susceptibility is closely related to the type of magnetic minerals.Most of the Tertiary red beds in the Lanzhou basin exhibit lower magnetic susceptibility,and the contribution of the magnetic susceptibility in sediments is mainly from ferrous minerals(such as magnetite)and ferromagnetic minerals(such as hematite),but because of magnetic minerals Content is not high,so the magnetic susceptibility value is generally low.(2)The electromagnetic parameters such as ARM,SIRM and HIRM in mudstone samples are higher than sandstone,indicating that the total content of magnetic minerals in mudstone is higher than that in sandstone.In the mudstone samples,both high coercivity and low coercivity magnetic minerals are contained,and the contribution of low coercivity magnetic minerals to its remanence is higher than that of high coercivity components.The magnetic minerals are mainly composed of SP and PSD particles The sandstone samples have lower magnetic mineral content than mudstone,and their high-order coercive and lowcoercive forces contribute to their remanence.(3)The values of I425 and I535 in the sandstone are relatively significant,while the values of I425 and I535 in the mudstone are relatively small,which indicates that the hematite and goethite in the sandstone are More than the amount of mud in the rock.The linear regression analysis of the Hm /(Gt + Hm)and its depth of mudstone and sandstone shows that the influence of distance on sandstone and mudstone is not significantly correlated,and the fitting degree is very low.According to previous studies,it is considered that Hm /(Gt +Hm)can be an indicator of climate,and Hm / Gt can be more effective as an indicator of climate.(4)The formation environment of sandstone is lacustrine sediment,magnetic minerals dissolved,resulting in relatively low magnetic susceptibility;mudstone formation environment for the lake,the analysis may be caused by surface runoff from the exposed surface of the debris material,magnetic Mineral content and species have a close relationship with provenance.