摘要：
白洋淀是华北平原最大的淡水湖泊,是研究全新世气候变化的理想区域.文章选择白洋淀东垒头剖面(厚382 em),在8个AMS-14C测年数据基础上,通过对其189个样品的地球化学元素、粒度和磁化率等指标分析,高分辨率地揭示了白洋淀地区全新世气候变化过程.研究结果显示:1)11335 ～ 10300 cal.a B.P.期间,CaO/MgO比值(多高于4.8)、(CaO+K2O+Na2O)/Al2O3比值(多高于1.3)、CaCO3含量(多高于12％)和中值粒径(多高于15 μm)均为整个剖面最大值,干旱指数(平均约为0.019)为剖面次高值,CIA值(多低于45)、Ti含量(多低于0.38％)和低频磁化率值(多低于10×10-8 m3/kg)为整个剖面的最低值,指示气候冷干,受新仙女木事件影响较大;2)10300～8500 cal.aB.P.期间,CaO/MgO比值、(CaO+K2O+Na2O)/Al2O3比值、干旱指数和中值粒径明显下降,CIA值、Ti含量、低频磁化率值均不同程度上升,指示气候向暖湿发展;3)8500～ 6000 cal.a B.P.期间,气候总体温暖湿润,干旱指数(平均达0.014)为剖面的最小值,CIA值和Ti含量较高,CaO/MgO比值、(CaO+K2O+Na2O)/Al2O3比值较低;但该阶段所有指标波动剧烈,8200 cal.aB.P.和6800 cal.aB.P.左右CaO/MgO比值、(CaO+K2O+Na2O)/Al2O3比值、干旱指数、CaCO3含量出现高峰值,CIA值和Ti含量出现低峰值,指示2次明显冷干事件;4)6000 ～ 4200 cal.aB.P.期间,CaCO3含量最低,但干旱指数较高,CaO/MgO比值、(CaO+K2O+Na2O)/Al2O3比值均有不同程度上升,指示气候湿润度有所下降;其中4500 cal.aB.P.为一次明显冷干事件,干旱指数呈现高峰值;5)4200～1035 cal.aB.P.期间,砂含量(多低于2％)、中值粒径(多低于10 μm)为剖面最小值;干旱指数、CaO/MgO比值、(CaO+K2O+Na2O)/Al2O3比值、CaCO3含量明显升高,指示气候向着凉干方向发展;干旱指数在2800 cal.aB.P.呈现高峰值,指示一次明显冷干事件,同时,该时段受人类活动影响,低频磁化率值(多高于20×10-8 m3/kg)明显高于其他时段.%Influenced by various factors,high-resolution sedimentary records overlap the whole Holocene in the North China Plain are lacking,that makes us have not enough knowledge about the environmental and climate change during the Holocene in the North China Plain,especially for the rapid change climate events.Baiyangdian is the largest freshwater lake in the North China Plain and an ideal area for studying the climate change during the Holocene.A profile(38°52′27.764″N,115°53′45.789″E;29 m a.s.l.)is selected at Dongleitou in the southwest Anxin County,Hebei Province,which was 382 cm in depth,the top of the profile(42 cm)was 1035 cal.a B.P.and the bottom (424 cm)was 11335 cal.aB.P.189 samples(from BD-22 to BD-210)were collected from Dongleitou profile,and geochemical elements,grain size and magnetic susceptibility analysis were used to reconstruct Holocene climate change based on the 8 AMS-14C dating data.The results are shown as follows:(1) From 11335 cal.a B.P.to 10300 cal.a B.P.,the ratio values of CaO/MgO(higher than 4.8),the ratio values of(CaO+K2O+Na2O)/Al2O3(higher than 1.3),the content of CaCO3(higher than 12％) and the median particle size(higher than 15 μm)reached to the maximum in the whole profile,the values of the drought index(average 0.019)were the second maximum in the whole profile,but the values of CIA(lower than 45),the content of Ti element(lower than 0.38％) and the values of magnetic susceptibility (lower than 10 × 10-8 m3/kg) were the minimum of the profile,indicating cold and dry climate in the study area,affected by YD event.(2)From 10300 cal.a B.P.to 8500 cal.a B.P.,the ratio values of CaO/MgO and(CaO+K2O+Na2O)/Al2O3,the values of the drought index,the content of CaCO3 and the median particle size all significantly declined,yet the values of CIA,the content of Ti element and the values of magnetic susceptibility increased in different degree,indicating that the climate became relative warm and wet.(3) From 8500 cal.a B.P.to 6000 cal.a B.P.,it was the most humid period with minimum of the drought index(average 0.014)and the high contents of CIA and Ti element and the low ratio values of CaO/MgO and(CaO+K2O+Na2O)/Al2O3,but all of them obviously fluctuated and the ratio values of CaO/MgO and (CaO+K2O +Na2O)/Al2O3,the values of the drought index,the content of CaCO3 appeared high peak values,while the values of CIA,the content of Ti element appeared low peak values at about 8200 cal.a B.P.,6800 cal.a B.P.,indicating two cold and dry events.(4)From 6000 cal.aB.P.to 4200 cal.a B.P.,the content of CaCO3 was the minimum in the whole profile,but the values of the drought index was higher,the ratio values of CaO/MgO and(CaO+K2O+Na2O)/Al2O3 increased,indicating humidity decreased,but at about 4500 cal.a B.P.,the values of the drought index were the highest,suggesting a cold and dry event.(5) From 4200 cal.a B.P.to 1035 cal.a B.P.,the content of sand (lower than 2％) and the median particle size (lower than 10 μm)were the minimum in the whole profile,the values of the drought index,the ratio values of CaO/MgO and(CaO+K2O+Na2O)/Al2O3 and the content of CaCO3 all clearly increased,indicating that the climate became cool and dry,the values of the drought index appeared a high peak value at 2800 cal.a B.P.,indicating an obvious cold and dry event;while the values of magnetic susceptibility(higher than 20× 1 0-8m3/kg) were higher compared with other periods,indicating intensive human activities.
