长江三峡地区一级阶地堆积物地球化学特征--以江津油溪剖面为例

Geochemical Characteristics of the Peleoenvironment of Sediment of the First Terrace of the Three Gorge of the Changjiang——A Case Study for the Youxing Profile of Jiangjin

采用14C法对江津油溪剖面长江三峡一级阶地上部砾岩层胶结年代进行测定以及填隙物的Fe2O3、FeO、CaO、MgO及Fe2O3/FeO等变化特征进行了分析,下部松散砾石层填隙物氧化物特征为:Fe2O3含量及Fe2O3/FeO比值较高,FeO、CaO、MgO含量较低;胶结砾岩填隙物的氧化物特征则相反。研究结果表明,本阶地的形成年代为距今13.4～40ka;晚更新世晚期的气候变化可能是剖面氧化物变化特征的原因。

The 14 C age dating method was applied to study the deposited age of the the first terrace of the Three Gorge of the Changjiang in Youxi profile,Jiangjin.The geochemical characteristics of oxides such as MgO,CaO,Fe2O3,FeO,Fe2O3/FeO were analyzed.It was found that the Fe2O3 and the Fe2O3/FeO ratio are high in the lower incompact gravel bed,whereas FeO、CaO、MgO are lower.The characteristics of the oxides in the diagenetic conglomerate are opposite.The 14 C age dating indicated that the deposited age of the first terrace was between 13.4ka.BP and 40.0ka BP.The geochemical results shown that the Jiangbei conglomerate might be deposited under a dry and cold climate during the last Glacial age in late Pleistocene,.and these geochemical characteristics recorded in cyclic sedimentations of this area reflected the changes of alluvial system dynamics,and implicated warm/wet-cold/dry cyclic changes in late Pleistocene.