The Pedogenetic Environment Changes Since The Middle-late Holocene In The Maqu Plateau Reflected By Geochemical Elements

The loess-paleosol-aeolian sequence since quaterary is the specific product which interacted by climatic conditions and sedimentary environment, and the essential of soil was that the chemical reset and migration. Accordingly, the disturibution of elements and the change characteristics of chemical parameter all can show the variety of pedogenetic environment directly. This article revealed the pedogenetic environment since the middle-late Holocene in Maqu Plateau from the angle of geochemical elements and the typical properties of soil. In this study, a typical aeolian deposit profile which named OL profile was studied using the measurement of element content, organic matter content, pH values and electrical conductivity, and discussed the distribution and changing characteristics of all indicators.The main results were following: the migration capabilities is Ca > Na > Si,constant element oxides MgO、K2O、Fe2O3 and trace elements Ga、As、Nb、Cu、Pb、Y、Ni、Nd、Zn、V、Ce、Cl、Ba、Cr、Rb、Zr、Mn was enrichment in paleosol,so which can indicate bio-pedogenesis, dissolving and and leaching action. Ancient climatic index could well reflect the drought-wet degree of pedogenetic environment.The Si O2/Al2O3 ratio, Na2O/K2 O ratio,(K2O+ Na2O+ CaO)/ Al2O3 ratio, Cu/Mn ratio,Sr/Cu ratio and Sr/Ba ratio in loess is higher than paleosol, on the contrary, the chemical weathering index(CIA),(Al2O3+ Fe2O3)/(RO +R2O) ratio and Rb/Sr ratio in paleosol is higher than loess and paleo-aeolian sand. The A-CN-K diagram showed that the OL profile had experienced an incipient stage of chemical wethering,accompanied by carbonate lenching and the depletion of mobile element Na and Ca,which indicated the alpine climate characteristics of Maqu Plateau. Relatively to loess and paleo-aeolian sand, the higher organic matter content in paleosol indicated that the climate is warm-humid and the pedogenesis is stronger in the period of the paleosol formation. pH values and electrical conductivity indicated that the rainfall was abundant in paleosol formation than loess formation in OL profile.Through the analysis and discussion of geochemical elements and the typical properties of soil of OL profile, and combined with14 C dating revealed the climate of the Maqu Plateau had changed in temperature cycle from cold-dry-cool-humid-warm-humid to cool-dry in 4.6 ka B.P., the pedogenic environmental evolution in the Maqu Plateau since the middle-late Holocene could be divided into 4 stages: intense aeolian activities before 4.6 ka B.P., aeolian activities weakened during 4.6-4.3 ka B.P.,sand dunes getting fixed and consolidated into soil during 4.3-0.3 ka B.P., and aeolian activities extreme after 0.3 ka B.P. to present.Through analysis and contrast, the recording of pedogenic environment and aeolian activities in OL profile was similar to other sedimentary methods such as lacustrine sediments in Tibetan Plateau, Qinghai Lake(QDST profile), Zoige pollen,Lake level change, and more fully revealed the pedogenic environmental evolution in the Maqu Plateau in 4.6 ka B.P.; Meanwhile, compared with ice core, Historical climate cold events in China, the results could exactly explain the pedogenic environmental evolution and aeolian activities in the Maqu Plateau has the very good response on global climate change.