河北平原北部蓟州区西南头营剖面地层沉积特征与沉积环境研究

Depositional characteristics and environment research of the Touying section in southwestern Jixian County,Northern Hebei Plain

笔者等通过详细测量河北平原北部天津市蓟州区西南部桑梓镇头营剖面,结合粒度分析数据、孢粉分析数据、^(14)C和光释光测年数据,系统分析了该剖面地层形成年龄和沉积特征。实测剖面显示地层可以划分为18层,沉积物以黏土质粉砂、粉砂质黏土、黏土为主。^(14)C和光释光测年数据显示该剖面沉积物主要为晚更新世晚期以来沉积。粒度分析结果显示14个粒度样品频率分布曲线均为不对称的单峰态,表明沉积物成分单一,为相对稳定的水能条件下形成;概率累积曲线以细粒型为主,样品主要由跃移总体和悬浮总体组成。根据孢粉组合特征,可将剖面划分为3个孢粉带,孢粉带Ⅰ:气候温和湿润;孢粉带Ⅱ:气候寒冷干旱;孢粉带Ⅲ:气候温暖湿润。实测剖面测年结果与古里雅冰芯氧同位素曲线作对比可知,剖面形成时代对应MIS3~MIS1阶段,头营剖面经历了暖—冷—暖的气候变化,与孢粉组合反映的气候特征一致。综上可知,头营剖面晚更新世以来沉积物应属漫滩或洼地相沉积,整体处于相对稳定的低水流条件,沉积环境稳定。

Objectives:The study of Quaternary sedimentary environment of different tectonic units in Hebei Plain is helpful to understand the change of sedimentary paleoenvironment.Dachang depression is located in the north of Hebei Plain,and the work on its sedimentary environment are few.We study the change of sedimentary environment since late Pleistocene in the Touying section in the northern Dachang depression,and to provide some references for understanding the evolution of sedimentary environment of Hebei Plain.Methods:The grain-size characteristics of the Touying section has been studied by grain size samples.The formation age of the profile was analyzed by ^(14)C and OSL dating.Samples were taken from the profile for sporopollen research.Results:The Touying section can be divided into 18 layers and the sediments are dominated by clayey silt,silty clay and clay.The probability accumulation curve is dominated by fine type,and the sample is mainly composed of saltation population and suspension population.^(14)C and OSL dating results show that the measured stratigraphic section be accumulated at the end of late Pleistocene.According to the characteristics of palynology assemblage,the profile can be divided into three palynology belts.Along sporopolen zone I,the climate was warm and moist.Along sporopolen zoneⅡ,the climate was cold and dry,Along sporopolen zoneⅢ,the climate was warm and moist.Conclusions:The comparison between the measured section dating results and the oxygen isotope curve of the Guliya ice core showed that the Touying section experienced a warm—cold—warm climate change,which was consistent with the climate characteristics reflected by the palynology assemblage.The age of the section corresponds to MIS3—MIS1 stage.The sediments of Touying section should belong to floodplain or depression facies since late Pleistocene.The Touying section was formed on relatively stable low-flow conditions and the sedimentary environment was stable.