江北砾岩的地球化学特征及其古环境恢复初步研究——以江津油溪剖面为例

Preliminary Geochemical Study of the Peleoenvironment of the Jiangbei Conglomerate——A case study for the Youxi Profile of the Jiangjin

江北砾岩是河流砾石层在地表经胶结形成的沉积岩，长期以来地学界对其成因未有定论．本研究采用^14C法对江津油溪剖面江北砾岩胶结年代进行测定，用滴定法和原子吸收光谱仪对填隙物的Fe2O3、FeO、CaO、MgO及Fe2O3／FeO变化特征进行了分析．研究结果表明，江北砾岩的胶结年代为距今1．34万-2．43万年。晚更新世晚期末次冰期的干冷气候可能是江北砾岩胶结成岩的主要原因；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．

The Jiangbei conglomerate is a kind of supergene cemented rock in the river gravel. Up to date, when and how the Jiangbei conglomerate was deposited is not clear. The ^14C age dating method was applied to study the deposited age of the Jiangbei conglomerate 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 were opposite. The ^14C age dating indicated that the deposited age of Jiangbei conglomerate was between 13.4 ka and 24.3 ka. The geochemical results showed that the Jiangbei conglomerate might be deposited under a dry and cold climate during the last glacial age in late pleistocene.