Late Holocene Human Activity Documented By Peat Deposits Of Tieershahan Wetland In The Altai Mountains,Northern Xinjiang

Northern Xinjiang has been thought as an important area for acient communications of various techniques and cultures between the West and the East,in part due to particular geographical locations,by which the adjacent regions are easily accessed,such as the Mongolian Plateau in the east,the Minusinskaya Kotlovina in the north,the hinterland of China via Urumqi City,and the Siberia along the Ertix River vally.In these regions,there were a number of prosperous Brozne-Iron civilization occurred.Peats have been recognized as an ideal geologic archive of atmospheric metal deposition,which can provide important information on human mining and metallurgical activity over the past.In this study,we selected the ombrotrophic peat deposits in the Tieershahan wetland and used AMS 14 C dating to establish the chronology of a sequential peat core.Heavy metal elements,ash accumulation flux and grian size of mineral components in the peat were measured.The heavy metal elements were employed to reflect human activity during the Holocene,on a basis of thoroughly understanding of input process of mineral debris to the peatland and of influences of grain size and post-deposition processes on elemental valiability and.The main conclusions are drawn as follows:1.The grain-size frequency distribution and the distributional pattern of rare earth elements(REE)of detrital particles from peat deposits are similar to those of typical loess deposits,suggesting that the mineral detrital particles were mainly transported by winds to the wetland.This is also demonstrated by the negative values of discriminant parameter of sedimentary environments.In addition,heavy metal elements along peat core are less affected by post-deposition processes.Furthermore,grain size of mineral detrital particles has little effect on variations in elemental compositions,such as Cu,Pb,Cd,Ni,and Cr,except for V.2.The elemental contents of Cu,Pb,Cd,Mo,Co,As and Zn exhibited a similar changing trend from 8900 to 5500 cal a BP.However,since 5500 cal a BP,Mo,Co,As and Zn decreased sharply and approximated to the average respective values of the Upper Continental Crust(UCC).However,remarkable increases in Cu,Pb,Cd occurred at 5500-2000,1350-1200 and 1100-700 cal a BP,which may be ascribed to input of heavy metals related to human mining and metallurgical activity in the study area.During the early Holocene(8900-5500 cal a BP),Mo,Co and As were less affected by human activity and hence taken as natural background values of these elements in the study area.In addition,Cu,Pb,Cd,Mo,Co and Asdisplay strong correlations among them during this period.The natural background values of Cu,Pb and Cd were calculated using linear regressions between Cu and Mo,Pb and Co,Cd and,As,respectively.Therefore,the abundance of Cu,Pb and Cd contributed by human activity are then calculated by subtracting the natural background values from the measured ones.3.During 5500-2000 cal a BP,the obvious enrichment in Cu,Pb and Cd may have been associated with a number of prosperous Brozne-Iron civilizations around the Altay Prefecture,Minusinskaya Kotlovina,Tuva and those upwind area.The mining and metallurgical activity during this period could enhance emissions of mineral dust and relevant metal elements,leading to enhancements of heavy metal elements in the peat deposit.The abrupt enrichment in Cu,Pb and Cd at 1350-1200 and 1100-700 cal a BP may have been associated with the large-amplitude exploitations of the Western Regions in the Tang dynasty and with the mining and metallurgical activity of Karahan Kingdom,respectively.The rapid increases in abundance of elements(e.g.Cu,Pb,Cd,Mo,As,Co,Zn and Ni)in the surface peat deposits probably resulted from the modern economic activity in northern Xinjiang.