【作者】 陈兰；

【导师】 胡瑞忠； 钟宏；

【作者基本信息】 中国科学院研究生院（地球化学研究所） ， 地球化学， 2006， 博士

【摘要】 中国南方古生代广泛分布富有机质的黑色页岩，分布层位较多（如下寒武统牛蹄塘组底部的黑色页岩、奥陶系五峰组页岩、志留系龙马溪组黑色页岩、泥盆系深水台间盆地的黑色碳质、硅质页岩，以及二叠系的黑色页岩、硅质岩等），并伴有Mo、Ni、PGE、V、Au、Ag等贵重金属元素富集层，尤其是湘黔地区下寒武统牛蹄塘组底部的黑色页岩，作为瞬时灾变沉积物，可与全球大洋缺氧事件对比。贵州省遵义地区黄家湾和湖南张家界地区柑子坪剖面为该地区较典型的剖面，前人已进行了大量的岩石地层、生物地层、元素地球化学研究工作，但沉积学方面尚缺乏系统性与较深入研究，特别是关于以黄家湾剖面为代表的浅水沉积体系与柑子坪剖面为代表的深水相黑色页岩沉积体系之间的时空关系缺乏统一的认识，且有机地球化学研究涉及甚少。因此，本文从沉积学和地球化学两方面，特别是有机地球化学方面，探讨了湘黔地区下寒武统底部牛蹄塘组黑色岩系的成因以及相应的灾变事件—大洋缺氧事件，取得如下认识： （1）本文对研究区下寒武统地层进行了较全面的清理，重新厘定了研究区下寒武统地层系统。下寒武统自下而上划分为牛蹄塘组、明心寺组、金顶山组和清虚洞组，其时代经历了梅树村阶、筇竹寺阶、沧浪铺阶和龙王庙阶，与西伯利亚地区同期沉积相比，分别对应晚Tommotian、Atdabanian、Botonian和Toyonian期。 （2）确定了研究区下寒武统岩石类型有碳酸盐岩、泥质岩和碎屑岩三大类。下寒武统下、中部泥质岩、粉砂岩及砂岩发育，且以泥质岩为主，少有碳酸盐岩发育，而上部清虚洞组灰岩（白云岩）发育。下寒武统牛蹄塘组黑色岩系主要由黑色页岩、石煤、硅质页岩、硅岩、粉砂岩、磷块岩、重晶石岩等组成，主要矿物组合为石英、伊利石和黄铁矿以及少量重晶石、磷灰石和方解石。从生物地层、岩石地层、年代地层来看，牛蹄塘组底部黑色页岩与南亚、西亚、欧洲、北美等地Tommotian期广泛分布的黑色页岩有很好的可对比性。 （3）基于对地层清理、古生物以及岩石学特征的详细研究，研究区下寒武统可划分为碎屑岩海相和碳酸盐岩海相两个沉积体系组。碎屑岩海相又分为滨岸、内陆棚、外陆棚、斜坡亚相；碳酸盐岩海相主要为开阔台地亚相。从时空上看，地层由老到新，粒度逐渐变粗，水体逐渐变浅，从外陆棚-斜坡、内陆棚到滨海，最后为开阔台地相：从西向东，由浅水相区的滨岸到内陆棚，最后到深水相区的外陆棚到斜坡。 （4）晚震旦世灯影组灰白色粉晶白云岩样品的SiO₂含量比较低，MgO、CaO、CO₂含量较高。牛蹄塘组黑色碳质泥岩、碳质页岩以SiO₂含量为主，其次为Al₂O₃和Fe₂O₃。微量元素含量具有如下特征：地层由老到新，从灯影组白云岩→牛蹄塘组磷块岩／硅质岩→多金属富集层，呈现出增加趋势，此后至黑色页岩又有回落。特征微量元素（如Mo、Ni、V、U等）及其比值（如V／（V+Ni）、V／Cr、Ni／Co、U／Th、δU等）显示这套富含有机质黑色页岩为热水沉积，其沉积环境为含氧量逐渐减少的贫氧-缺氧的还原环境。 （5）稀土元素总量（∑REE）从6.67ppm变化到481ppm，平均含量为123ppm，轻稀土相对比较富集。经PAAS标准化的稀土配分模式曲线具有近于水平或略显右倾特征。灯影组Ce异常值均小于-0.10，代表当时海水处于氧化阶段。而牛蹄塘组底部和上部Ce异常值大于-0.10，接近0，代表弱的缺氧沉积环境。对于牛蹄塘组中部，其值小于-0.10，说明缺氧环境持续了一段时间后，海洋出现了一个短暂的充氧期。根据Ce异常和参考海平面，研究区晚震旦世-早寒武世可识别出3个主要海平面升降旋回。而Eu异常为0.002-1.16，大多数样品更多还原

【Abstract】 The Paleozoic is marked by the occurrence of anomalously organic-carbon-rich laminated shales in large parts of South China and in the world as well. These sediments, enriched in the precious metal elements such as Mo, Ni, PGE, V, Au, Ag and so on, are distributed in widespread strata including the Niutitang Formation of the Lower Cambrian, Wufeng Formation of the Ordovician, Longmaxi Formation of the Silurian, Devonian and Permian. Especially, the black shales of the lower part of Niutitang Formation from the Hunan-Guizhou area were regarded as instantaneous and catastrophic deposition, coincident with the global Oceanic Anoxic Event (OAE). Therefore, this study on the black rock series possesses important theoretic significance and potential economic implication. Two typical sections of Huangjiawan (Guizhou Province) and Ganziping (Hunan Province) have been previously studied on litho- and biostratigraphy, elemental geochemistry, but the temporal and spatial relationships between the Huangjiawan shallow sedimentary systems tract and the Ganziping deep black shales sedimentary systems tract have not been reached unified views. Particularly, the records in organic geochemistry of the Early Cambrian (Tommotian) black shales in South China have received less attention. Based on above-mentioned circumstance, this paper chooses the Early Cambrian black shales in the Hunan-Guizhou area as studying object. Focusing on the sedimentology and geochemistry, especially the organic geochemistry, the present study discusses the genesis of Niutitang Formation black shales and Tommotian oceanic anoxic event, and draws the following conclusions.(1) On the basis of field works in the Hunan-Guizhou area, combining previous achievements, the Early Cambrian stratigraphical systems are built from lower to upper as follows: the Niutitang Formation, Mingxinsi Formation, Jindingshan Formation and Qingxudong Formation with mass occurrences of arthropods, sponges, trilobitas, bacterial colonies, etc. corresponding to Meishuchunian, Qiongzusian, Langcangpuian and Longwangmian, respectively. Compared with the contemporaneous deposits occurred in Siberian, the Early Cambrian in this area corresponds to Tommotian, Atdabanian, Botonian and Toyonian, respectively.(2) Rock types of the Early Cambrian strata consist of carbonates, argillaceous rocks and clastic rocks. The argillaceous rocks, siltstones and sandstones were devoloped in the lower-middle Lower Cambrian with a few intercalated limestones horizons, while the limestones and/or dolomites in the Qingxudong Formation of the upper Lower Cambrian. The Niutitang Formation important black rock series of the Lower Cambrian, are composed of black shales, stone coal, siliceous shales, silicalites, siltstones, phosphorites, baritic rock. Their mineral compositions are mainly quartz, illite and pyrite with subordinate barite, apatite and calcite. According to the bio-, litho- and chronostratigraphy, the synchronous black shale facies also occurred in South and West Asian, European, North Amercian and so on.(3)The Lower Cambrian sedimentary facies in the study area were characterized by clastic更多还原