ENVIORNMENT RECONSTRUCTION OF MID-HOLOCENE PALEO-LAKES IN ZHENGZHOU AND SURROUNDING REGIONS AND THE SIGNIFICANCE FOR HUMAN CULTURAL DEVELOPMENT IN CENTRAL CHINA
Black lacustrine peat deposits have been found at several sites of Zhengzhou in a depth of about 4 ~12m.This paper selected 4outcrops and 17sediment cores,for analysis of environmental proxies of sedimentology,environmental magnetism,geobiology (pollen and snall shells)and geochemistry.14C, TL,and OSL dating indicates that the lake occurred 3 ~ 8kaBP,in Mid-Holocene.Lake deposits are composed of gray-black silty clays.The percentage of clay in the layer is higher than that in other layers. High clay content is correlated to low magnetic susceptibility,which means that there was less magnetic heavy minerals coming in,indicating a weak hydrodynamic environment.Pollen of aquatic plants account for 19.4% of the total,including Typha,Polygonum,Nymphoides,Myriophyllum and Potamogeton. TOC content in the lacustrine layers reaches 21.6%on average,and in some of the layers it may be as high as 29.4%.The C-index(function of various chemical elements)is synchronously fluctuated with fine particles. The higher clay content and higher C-index,the more humid climate.This means that it was relatively high in precipitation,with high vegetation coverage,and lower soil erosion during early-mid Holocene than in the periods after ca.3kaBP Some historical documents before 220BC.mentioned some ancient lakes in the area for examples,the Xingze and the Putianze,eventhough the locations of the paleolakes remain unknown up to date.All the evidence supports the existence of Mid-Holocene paleolakes, whose range and area are quantitatively estimated in the this paper.The results of this study will certainly provide technique support for cultural archeological studies and relic excavation.