Chemical weathering degree of the Late Holocene aeolian loess and climate change in Maqu Valley
After extensive and detailed field investigation in the Zoige Basin,a Late Holocene aeolian loess-paleosol section at Laoqiaoxi(LQX)site on the first river terrace(T1)of the Yellow River in the Maqu reach was selected for research.The grain-size distribution,magnetic susceptibility,the distribution characteristics of major elements and the geochemical behavior of the loess surface(such as CIA,alkali degradation coefficient,leaching coefficient,residual coefficient,calcium magnesium ratio,sodium potassium ratio,rubidium strontium ratio,etc.)are studied.Based on the stratigraphic-chronological framework by using OSL dating of aeolian loess in the first order terrace of the Yellow River,this paper attempts to reveal the characteristics of chemical weathering processes of aeolian loess and recorded environmental changes since the Late Holocene.The results showed that:(1)LQX section was formed in the Late Holocene,and its stratigraphic-chronological framework is:Fluvial sand(FS,>3.0 ka)→Aeolian sand(AS,3.0-2.5 ka)→ Lower loess(L02,2.5-2.3 ka)→Lower soil(MS1,2.3-1.6 ka)→ Upper loess(L01,1.6-0.4 ka)→ Surface soil(MS0,0.4 ka-present).(2)LQX profile is in the lower chemical weathering stage dominated by the weathering of plagioclase,and the order of intensity of weathering and pedogenesis in different stratigraphic units is:AS is the weakest layer → L02 gets weaker →MS1 is the strongest layer → L01 slightly gets weaker → MS0 gets stronger.(3)Since the Late Holocene,the Maqu Valley has experienced the climatic changes:cold and dry period(3.0-2.5 ka),cool and dry period(2.5-2.3 ka),warm and wet period(2.3-1.6 ka),cold and dry period(1.6-0.4 ka),warm and wet period(0.4 ka-present),which is in good agreement with the paleoclimatic information records of the Tibetan Plateau and other areas.This findings provide the first evidence for constructing the trajectory of climate evolution in the region since the Late Holocene,and further enrich the paleoclimate research content in the northeastern Tibetan Plateau.
the first river terrace of the Yellow Rivermajor elementsLate Holoceneclimate changeLQX profile