Chemical Weathering Characteristics of Tuojiawan Profile in the Upper Hanjiang River Valley and Its Environmental Significance

Key words: 
• major elements /
• chemical weathering /
• OSL age /
• climate change /
• Upper Hanjiang River

Abstract: The chemical characteristics of major elements and magnetic susceptibility of Tuojiawan profile in the upper Hanjiang River are studied. The change of the indexes revealed that major elements geochemical behavior and the corresponding laws of climate change in the Upper Hanjiang River. With X-Ray fluorescence spectrometer, MS-2 magnetic susceptibility instrument measured element content and magnetic susceptibility values. Results show that: The major elements are SiO₂, Al₂O₃ and Fe₂O₃. Na,Ca,Mg,Si,K are leached out while Ti,Fe,Al relatively enriched in the paleosol S₀. The element mobility and migration ability of the major elements are ranked in the followed order: Na > Ca > Mg > Si > K > Al > Fe. Magnetic susceptibility values showed obvious peak value in 228~260 cm and 294~370 cm depth, the variation in content of Fe and Al elements and chemical alteration index curve and magnetic susceptibility curve showing a high consistency, at this depth are characterized by high value. It was shown that the chemical weathering intensity of this depth was obviously higher than that of Malan loess, close to the palaeosol(S₀), belonging to the weak palaeosol(L₁~S₁ and L₁~S₂).The age range of L₁~S₁ and L₁~S₂ was 27.5~21.5 ka B.P.. The change of the indexes showed the climate and pedogenic environmental changed since Pleistocene. Including the cold and arid glacial and a short time the climate was warm and wet in the glacial period(27.5~21.5 ka B.P.), the gradually intensified southeast monsoon during the early Holocene periods, the strongest monsoon in the mid-Holocene, and the monsoon recession and the climate drying during the late Holocene.