Grain-size characteristics and sedimentary environment change of JZ-2010 section in Jianghan Plain, Hubei Province

Abstract

通过对江汉平原JZ-2010湖相沉积剖面AMS¹⁴C年代的精确测定与校正,以及代用指标粒度、磁化率的分析和研究,重建了研究区12.76 cal ka BP以来的环境演变过程:1)12.76-6.70 cal ka BP,区域环境处于偏干的晚冰期向湿润的早全新世发展阶段.2)6.70-4.47 cal ka BP,区域环境湿润,为湿度配置最佳的全新世适宜期,这是大溪文化向屈家岭文化转变时期自然背景.3)4.47-3.67 cal ka BP,区域气候环境偏干,其中经历了明显的4.2 cal ka BP干旱事件.4)3.67-1.22 cal ka BP时期,环境向湿润发展;在2.5 cal ka BP左右水动力条件明显变强,此时正对应于古云梦泽扩张时期.5)1.22 cal ka BP后,研究区处于湖泊面积减小的干旱时期;人类活动带来的影响达到高峰,围湖造田等农业活动也是江汉平原湖群趋于衰退的重要原因之一.;Based on the precise measurement and correction of AMS ¹⁴C dating ages combined with the analysis and research of environmental proxies such as grain-size, magnetic susceptibility from the lake sedimentary records of JZ-2010 section in the Jianghan Plain of Hubei Province, this paper reconstructs the sedimentary paleoenvironment of the study area during last 12.76 cal ka BP:1) 12.76-6.70 cal ka BP. All the proxies show that sedimentary grain size gradually turned fine, which reflects a period of high water level and extended lake area. The regional environment turned from dry Late Glacial to fairly wet Early Holocene, characterized with transition and fluctuation. 2) 6.70-4.47 cal ka BP. The regional environment is moist in the whole phase, which is the Holocene Optimum with optimal moist. The regional environment is the natural background of Daxi Culture transitioning to Qujialing Culture, moreover human settling into the heart area of Jianghan Plain. 3) 4.47-3.67 cal ka BP. The regional environment is in dry conditions. Among this stage, all the proxies distinctively figured out the global 4.2 cal ka BP dry event in the Jianghan Plain. 4) 3.67-1.22 cal ka BP. Regional environment became wet again and hydrodynamic conditions obviously stronger around 2.5 cal ka BP which correspondence to the ancient Yunmeng Marsh expansion recorded in Pre-Qin historical documents. 5) Since 1.22 cal ka BP, lakes in Jianghan Plain have shrunk showing relatively dry environment conditions. These environmental changes appeared to be largely caused by anthropogenic factor and reached its peak during the Tang and Song Dynasty. Settlement development and agricultural activities such as reclaiming farmland has also been one of the important reasons reduced the lakes area of Jianghan Plain.