埃迪卡拉纪末期华南盆地深水环境的微量元素约束  

Trace element constraints on deep-water redox conditions of the terminal Ediacaran in south China basin

作　　者：常华进[1] 储雪蕾[2] 黄晶[2] 冯连君[2] 

机构地区：[1]青海师范大学生命与地理科学学院青藏高原环境与资源教育部重点实验室,西宁810008 [2]中国科学院地质与地球物理研究所,北京100029

出　　处：《兰州大学学报（自然科学版）》2011年第5期17-23,29,共8页Journal of Lanzhou University(Natural Sciences)

基　　金：国家自然科学基金项目(41002011;40873007;40603021);中国科学院知识创新工程项目(KZCX3-SW-141);青海师范大学中青年教师科研基金项目

摘　　要：对沉积于埃迪卡拉纪末期(551～542 Ma)华南盆地深水的老堡组硅岩样品中微量元素进行了研究.老堡组硅岩的元素地球化学特征显示岩石中微量元素主要来源于沉积水体,它们的质量分数和相关比值具有良好的环境指示意义.老堡组硅岩微量元素具有极低的w(Th)/w(U)(0.15～1.36,平均0.78),高的w(V)/(w(V)+w(Ni))(0.58～0.91,平均0.77),氧化还原敏感元素富集(U,V,Mo的富集系数较高),Mn的质量分数(10.9×10^(-6)～27.6×10^(-6))和富集系数均低的地球化学特征.这些特征表明埃迪卡拉纪末期华南盆地深水是缺氧的.然而,硅岩样品相对低的U,V,Mo质量分数以及缺乏黄铁矿指示了当时深水不是硫化的,而是缺氧含铁的,这种水体环境可能为多细胞后生动物的出现和快速演化提供了必要条件.A detailed trace element study of chert from the Laobao formation, which is a terminal ediacaran （551-542 N/a） succession in south China deposited in deep-water basinal setting, was reported in this paper. The element geochemical features of Laobao chert show that the redox-sensitive trace elements in the chert were authigenically concentrated in water column and their concentrations thus are excellent indicators of ancient redox conditions. The Laobao chert was characterized by very low w（Th）/w（U） （0.15-1.36, avg 0.78） and high w（V）/（w（V）＋w（Ni）） （0.58-0.91, avg 0.77）, enrichment of redox-sensitive trace elements （high enrichment factors of U, V, Mo）, and low concentration of Mn （10.9× 10^-6-27.6× 10^-6） and their enrichment factors. All of these features suggest that the deep-water of the terminal ediacaran in south China basin was anoxic. However, the relatively low concentrations of redox-sensitive trace elements and shortage of pyrite suggest that the deepwater in the Laobao stage was not sulfidic. The new geochemical results in this text reveal that the deep-water of the terminal ediacaran in south China basin was ferruginous, and could create necessary conditions for the emergence and rapid evolution of multicellular metazoans.

关 键 词：氧化还原环境 硅岩 微量元素 华南 埃迪卡拉纪 

分 类 号：P595[天文地球—地球化学]