The chemical weathering intensity and element migration features of the Xiashu loess profile in Zhenjiang are studied in this paper.（1）The Xiashu loess profile underwent moderate chemical weathering.It seems that th...The chemical weathering intensity and element migration features of the Xiashu loess profile in Zhenjiang are studied in this paper.（1）The Xiashu loess profile underwent moderate chemical weathering.It seems that the precipitation is a more important factor than the temperature in controlling the process of the chemical weathering.（2）The major elements such as Si,K,Na,Ca,Mg,Mn and P were migrated and leached,while the elements Fe and Ti were slightly enriched.The migration features of the major elements reveal that the Xiashu loess finished the primary process of chemical weathering characterized by leaching of Ca and Na,and almost reached the secondary process characterized by leaching of K.Except the elements Sr and Ga,other trace elements such as Th,Ba,Cu,Zn,Co,Ni,Cr and V were enriched.It might be caused by both the biogeochemical process and the adsorption of trace elements by clay mineral and organic materials.（3）The difference of element migration down the Xiashu loess profile reveals that the climate was warm and wet at the early-middle stage of the middle Pleistocene.At the end of the middle Pleistocene,it became dry and cool.At the early stage of the Late Pleistocene,the paleoclimate became warm and wet again.As a whole,the paleoclimate generally became drier and cooler in this region from the beginning of the middle Pleistocene.展开更多
Mineralogical,physical and chemical analyses of the soils derived from Xiashu loess were carried out.The primary minerals of these soils were found to be mainly composed of light minerals,such as quartz,feldspar and m...Mineralogical,physical and chemical analyses of the soils derived from Xiashu loess were carried out.The primary minerals of these soils were found to be mainly composed of light minerals,such as quartz,feldspar and mica,with traces of heavy minerals.Clay minerals,more complicate in composition,were dominated by hydromica,accompanied by smectite,vermiculite,chlorite,kaolinite,2:1/1:1 randomly interstratified minerals and small amounts of quartz,goethite,lepidocrocite and hematite,Clay minerals were characterized by low crystallinity and fine particle size.In light of the quartz/feldspars ratio of the 0.01-0.05mm silt fraction,and the clay mineral composition,the freeness of iron oxide,and the silica/ sesquioxide and silica/ alumina ratios in <0.002mm clay fraction,it is concluded that the weathering intensity of these soils was lower than those of red soil and yellow earth,but higher than that of brown earth,and that the soil allitization,depotassication and hydroxylation of clay minerals increased from west to east and from north to south geographically.However,this general tendence did not coincide exactly with the gradual alteration of the geographic coordinates,and in some places,a reverse tendency also appeared,which could be attributed to the influence of some soil forming factors such as parent material and microtopography.展开更多
The Xiashu loess is a typical Quaternary eolian deposit in southern China and represents an important terrestrial paleoclimate archive in this low-latitude monsoon region. However, the chronological framework of Xiash...The Xiashu loess is a typical Quaternary eolian deposit in southern China and represents an important terrestrial paleoclimate archive in this low-latitude monsoon region. However, the chronological framework of Xiashu loess deposition has yet to be established. Determining the timing of the onset of Xiashu loess deposition will allow researchers to better understand late Quaternary aridification across the Asian continent, the evolution of the East Asian monsoon and regional environmental changes in subtropical regions. Therefore, in this study, a systematic chronological study of the Xiashu loess is conducted to answer this question. For the first time, magnetostratigraphic classification reveals that the Matuyama/Brunhes(M/B) reversal is present in the Xiashu loess at two sites in Jiangsu Province, the Qingshan profile at Yizheng and the Dagang core in Zhenjiang.Based on the results of magnetostratigraphy and optically stimulated luminescence(OSL) dating, the age of the lower boundary of the Xiashu loess is estimated to be approximately 0.9 Ma. Consequently, this Xiashu loess deposit is the oldest reported to date and is comparable in age to the red soil deposit in Xuancheng, Anhui Province. The onset of Xiashu loess deposition by 0.9 Ma represents the further expansion of arid range in Asia in the late Quaternary in response to significant aridification and winter monsoon strengthening in this subtropical region. We suggest that these climate changes were primarily driven by global cooling and an increase in high-latitude ice volume in the Northern Hemisphere and that the initiation of Xiashu loess accumulation was a regional response of southern China to the 0.9 Ma global cooling event.展开更多
基金National Natural Science Foundation of China, No.40401006 Open Foundation of State Key Laboratory of Loess and Quaternary Geology, No.SKLLQG0304 Experimental Foundation of Nanjing University
文摘The chemical weathering intensity and element migration features of the Xiashu loess profile in Zhenjiang are studied in this paper.（1）The Xiashu loess profile underwent moderate chemical weathering.It seems that the precipitation is a more important factor than the temperature in controlling the process of the chemical weathering.（2）The major elements such as Si,K,Na,Ca,Mg,Mn and P were migrated and leached,while the elements Fe and Ti were slightly enriched.The migration features of the major elements reveal that the Xiashu loess finished the primary process of chemical weathering characterized by leaching of Ca and Na,and almost reached the secondary process characterized by leaching of K.Except the elements Sr and Ga,other trace elements such as Th,Ba,Cu,Zn,Co,Ni,Cr and V were enriched.It might be caused by both the biogeochemical process and the adsorption of trace elements by clay mineral and organic materials.（3）The difference of element migration down the Xiashu loess profile reveals that the climate was warm and wet at the early-middle stage of the middle Pleistocene.At the end of the middle Pleistocene,it became dry and cool.At the early stage of the Late Pleistocene,the paleoclimate became warm and wet again.As a whole,the paleoclimate generally became drier and cooler in this region from the beginning of the middle Pleistocene.
文摘Mineralogical,physical and chemical analyses of the soils derived from Xiashu loess were carried out.The primary minerals of these soils were found to be mainly composed of light minerals,such as quartz,feldspar and mica,with traces of heavy minerals.Clay minerals,more complicate in composition,were dominated by hydromica,accompanied by smectite,vermiculite,chlorite,kaolinite,2:1/1:1 randomly interstratified minerals and small amounts of quartz,goethite,lepidocrocite and hematite,Clay minerals were characterized by low crystallinity and fine particle size.In light of the quartz/feldspars ratio of the 0.01-0.05mm silt fraction,and the clay mineral composition,the freeness of iron oxide,and the silica/ sesquioxide and silica/ alumina ratios in <0.002mm clay fraction,it is concluded that the weathering intensity of these soils was lower than those of red soil and yellow earth,but higher than that of brown earth,and that the soil allitization,depotassication and hydroxylation of clay minerals increased from west to east and from north to south geographically.However,this general tendence did not coincide exactly with the gradual alteration of the geographic coordinates,and in some places,a reverse tendency also appeared,which could be attributed to the influence of some soil forming factors such as parent material and microtopography.
基金supported by the National Natural Science Foundation of China(Grant Nos.41571188,41671191,41690111&40971004)
文摘The Xiashu loess is a typical Quaternary eolian deposit in southern China and represents an important terrestrial paleoclimate archive in this low-latitude monsoon region. However, the chronological framework of Xiashu loess deposition has yet to be established. Determining the timing of the onset of Xiashu loess deposition will allow researchers to better understand late Quaternary aridification across the Asian continent, the evolution of the East Asian monsoon and regional environmental changes in subtropical regions. Therefore, in this study, a systematic chronological study of the Xiashu loess is conducted to answer this question. For the first time, magnetostratigraphic classification reveals that the Matuyama/Brunhes(M/B) reversal is present in the Xiashu loess at two sites in Jiangsu Province, the Qingshan profile at Yizheng and the Dagang core in Zhenjiang.Based on the results of magnetostratigraphy and optically stimulated luminescence(OSL) dating, the age of the lower boundary of the Xiashu loess is estimated to be approximately 0.9 Ma. Consequently, this Xiashu loess deposit is the oldest reported to date and is comparable in age to the red soil deposit in Xuancheng, Anhui Province. The onset of Xiashu loess deposition by 0.9 Ma represents the further expansion of arid range in Asia in the late Quaternary in response to significant aridification and winter monsoon strengthening in this subtropical region. We suggest that these climate changes were primarily driven by global cooling and an increase in high-latitude ice volume in the Northern Hemisphere and that the initiation of Xiashu loess accumulation was a regional response of southern China to the 0.9 Ma global cooling event.
