Study On The Causes Of The Loess - Like Material In The Jinshajiang River Valley And Its Environmental Significance

Loess is one of the most carrier employed in climate change research, and is important in understanding the history of regional climate change. Based on the research of various physical and chemical properties, it is easy to know the important information from formation factors, material sources, and formation history of Loess. The thesis select Tao Yuan, Yuan Mou, and Qiao Jia loess-like sediment in the Jinsha River Valley as the research object, based on wild investigation and sampling, and we analysis particle size, geochemical elements, mineral composition, structural formation, wet quartz and chromaticity, and compare the difference between it and this regional river sediments, which discusses the reason of loess formation and the material source, and reveals the history of formation and evolution in the Jinsha river dry-hot valley(DHV).(1) Loess substance, including Tao Yuan, Yuan Mou, and Qiao Jia, are mainly distributed in less than 1600 m river valley, and we find that there is no loess substance distributed in non-DHV. Meantime, Tao Yuan loess substance is distributed in certain altitude from 1280 to 1380 m, loess substance in Yuan Mou is distributed in altitude from 1200 to 1600 m, and loess substance for Qiao Jia is distributed in altitude form 921-1400 m.(2) In comparison with the quaternary typical eolian loess-Malan loess, we fond that their particle size are both similar, with their main composition form 10 to 50 um. However, compared with adjoin lake sediment and rock, we fond they are different. Loess substance is mainly comprise of silty, and the content from 10 to 50 um is comparatively rich, whose grain size is similar to eolian loess. It is potentially associated with eolian. In addition, according to the mineral composition, we find that their compositions are alike, that reveals the sediment comes from elian sediment.(3) Through the geochemical elements comparison between loess substance in DHV and its facies sediments, we fond that their major elements and trace elements are very similar to each other. According to the trace elements features, we divided them into three models: the content including W, P, Cr, Co, is slightly smaller than the lake sediments; the content from loess substance, including Ba, Mn, V, Zn, is slightly larger than the lake sediment; their content, such as Zr, Rb, Ni, Cu, Nb, Hf, and Sr, is almost similar. But the content from loess substance is different form surrounding material substances. Additionally, the loess substance and facies sediments are alike in quartz particle morphology, suggesting that dust in wind transported to the loess area, better to inherit the quartz particle morphology. Therefore, we are sure that loess substance comes from facies sediments.(4) Based on the paleomagnetic chronology analysis, we deem that the age of Jin Sha river loess materials is about the end of the early Pleistocene to early middle Pleistocene.(5)Through the traits of loess formation and formation age, we are sure that the process of DHV experiences two stages: ?from early Pleistocene to early middle Pleistocene, due to the Qinhai-Tibet plateau uplift and fast river division, the process makes relative elevation difference increase, and results in the formation of DHV. When rivers incised to 1600 m, the climate is becoming dry, suggesting the river valley is formatting. ?from the end of the early Pleistocene to early middle Pleistocene, with the incessant incision of the Jin Sha river, the river valley foehn effect is obvious, and there is loess substance adjusting to the climate on the river terrace, all of which suggest the climate tend to become dry, half-dry, and the DHV is forming.