Preliminary Study On The Evolution Of Sedimentary Environment Of Ancient Lake Qingqiu In Southwestern Shandong Province During The Late Holocene

Ancient Lake Qingqiu is located in the Central and Northern China Plain,which is very sensitive to the changes of the East Asian summer monsoon owing to its location.During the historical periods,it was frequently affected by the repeated overbank flooding and levee breaches of the Lower Yellow River as well as human activities under the background of climate change,making it an ideal site for reconstructing the process of environmental evolution and its relationship with human culture in this region.In this thesis,three drill cores(QQGD-I?QQGD-II?QQGD-III)were obtained from Ancient Lake Qingqiu and one archaeological profile(QQGD-N)at the archaeological site.The QQGD-II borehole were taken as the main research object,a multi-stratigraphical study(e.g.,grain size,magnetic susceptibility,and chemical elements)in conjunction with high-resolution AMS-¹⁴C dating was conducted,to reconstruct the depositional environment and its relationship with human activities during the late Holocene.The results are summarized as followings:(1)Using the method of grain size frequency distribution curve and cumulative probability curve of the sediments and combined with the lithology characteristics,the sedimentary environment of the study site(QQGD-II)can be divided to six characteristic facies:1310-1000 cm(culture layer);1000-950 cm(floodplain sedimentary environment);950-914 cm(shallow lacustrine sedimentary environment);914-885 cm(culture layer);885-849 cm(floodplain sedimentary environment);849-676 cm(shallow lacustrine sedimentary environment),676-0cm(floodplain sedimentary environment);(2)Integrating multi-stratigraphical study(e.g.,grain size,magnetic susceptibility,chemical elements)in conjunction with high-resolution AMS-¹⁴C dating as well as historical documents,we infer that Ancient Lake Qingqiu has experienced six distinct stages of environment change and its relationship with human activities during the late Holocene.The results show that less precipitation and weaker erosion prevailed in the Qingqiu catchment under the dry climate conditions in the study area during 3678?1104cal yr BP,the flooding of the Yellow River rarely affected the Lake Qingqiu area.As a result,the ancient people lived adjacent to the lowland of the Qingqiu mound site;Subsequently,precipitation increased and the Qingqiu catchment erosion became stronger during 1104?804 cal yr BP,corresponding to the“Medieval Warm Period”.Meanwhile,the Yellow River floods repeatedly flowed into Ancient Lake Qingqiu,Consequently,the ancient people migrated to highland of the Qingqiu mound site;during 804?669 cal yr BP,corresponding to the transitional stage from the“Medieval Warm Period”to the“Little Ice Age”,precipitation began to decrease,the erosion of the catchment was relatively weak and low lake level prevailed;during 669?562 cal yr BP,corresponding to the early Little Ice Age,the watershed erosion was weak under the cold and dry climate,the region of human occupation extended to the lowland of the Qingqiu mound site again;during562?536 cal yr BP,dry-wet climate fluctuated remarkably,and Ancient Lake Qingqiu was affected by the Yellow River flooding again,the ancient people moved to the highland of the Qingqiu mound site again;during 536 cal yr BP?1855 AD,corresponding to the Little Ice Age,the lake experienced low level under dry and cold climate conditions.Because their previous experience of fighting against flooding,the ancient people still choose to live on the highland of the Qingqiu mound site.(3)The environment evolution of Ancient Lake Qingqiu was influenced by climate changes,the Yellow River overbank flooding,and human activities.Under the background of climate change,the Yellow River overbank flooding and human activities were the main causes for the sedimentary environment evolution of Ancient Lake Qingqiu.The above results have important scientific and practical significance for understanding the evolution of sedimentary environment in southwest of Shandong Province,revealing the relationship between early human civilization and environmental changes,and better understanding the impact of environmental change on early civilization.