渝东南及周边早寒武世黑色岩系岩石地球化学特征及成因

GENESIS AND PETRO-GEOCHEMICAL CHARACTERISTICS OF THE LOWER CAMBRIAN BLACK SHALE SERIES IN THE SOUTHEAST OF CHONGQING AND TTS ADJACENT AREA

针对渝东南及周边早寒武世黑色岩系属中国南方震旦纪之后大规模海侵产物的岩石地球化学研究结果表明:其黑色岩系的岩石地层单位由下至上涉及牛蹄塘组、明心寺—金顶山组及清虚洞组;其特征显示:K2O,Al2O3含量相对较高,MnO含量相对较低;B含量中等,分异性不强;Ba较为富集;Co,Ni,Zn亏损较大,由底至顶三者含量均有增加趋势;稀土总量不富集,轻稀土相对富集;由底至顶δEu表现为不明显的负异常,到明显的正异常,再到负异常;δCe绝大多数表现为不明显的负异常。岩石地球化学特征参数及相关图解表明,区内早寒武世黑色岩系形成于由缺氧还原状态逐步过渡至弱氧化状态条件下,浅海中水体稍深的外陆架环境,为正常海水与热水沉积作用的混合产物,热水主要来自于循环的热的海水。

The Lower Cambrian black shale series is a large-scale transgressive product after Sinian（Edicarian）made up of Niutitang Formation,Mingxinsi-Jindingshan Formation and Qingxudong Formation in the southeast of Chongqing and its adjacent area.The petro-geochemical characteristics show that,the content of K2O and Al2O3 are relative high,MnO is relative low;B is moderate,which has lower differentiation;Ba is relative abundant;Co,Ni and Zn are deficit,but they are continuously increasing from bottom to top.REE is very low and LREE is relative abundant.δEu shows unconspicuous negative anomaly to conspicuous positive anomaly to negative anomaly,and δCe mostly shows unconspicuous negative anomaly from the bottom to top.The petro-geochemical characteristics and their diagrams indicate that,the Lower Cambrian black shale series was deposited in the outer shelf of shallow sea,under the transitional condition from hypoxia-reduction to weak oxidation,resulted from the mixing between normal seawater and hot seawater sediments mostly coming from the cycling hot seawater.