扬子地区古生代主要烃源岩有机质富集的环境动力学机制与差异  

Environmental dynamics of organic accumulation for the principal Paleozoic source rocks on Yangtze block

作　　者：陈代钊[1] 汪建国[1] 严德天[2] 韦恒叶[1] 遇昊[1] 王清晨[1] 

机构地区：[1]中国科学院地质与地球物理研究所油气资源研究重点实验室,北京100029 [2]中国地质大学(武汉)资源学院武汉430074

出　　处：《地质科学》2011年第1期5-26,共22页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：国家重点基础研究发展计划“973”项目(编号:2005CB422101);国家自然科学基金项目(编号:40839907)资助

摘　　要：在扬子地块古生界发育了3套区域性的优质烃源岩,即:下寒武统、上奥陶统—下志留统、二叠系(中、上二叠统)。下寒武统烃源岩主要由硅质岩(留茶坡组)和上部的硅质泥岩、碳质泥岩(或石煤)(牛蹄塘组)组成。早寒武世在台—盆转换带(或台地边缘)广泛发育的海底热液活动,喷流出大量的富硅流体,使大量硅岩得以在台缘外侧——盆地区沉淀;同时,热液活动会释放出大量富H_2S、CO_2和金属元素的缺氧流体到海洋和大气中,使大气CO_2浓度和海平面大幅上升,深部富营养海水随上升洋流被携带至浅海,使生物产率增加、海洋缺氧进一步恶化,促使大量有机质得以埋藏和保存。上奥陶统—下志留统烃源岩主要由五峰组和龙马溪组黑色页岩夹硅质页岩组成,形成于奥陶纪—志留纪转折期的高海平面期,气候温暖;扬子与华夏陆块的加速拼接使得东南侧陆域扩大,在扬子地块内部形成了隆—凹相间的陆表海环境(或陆棚),水体循环受阻,从而强化了海水分层;而温暖的气候条件使化学风化作用增强,陆源营养输入量增加,并引起生物产率增加,但过量的陆源物质输入会造成有机质的稀释。这些因素造成了该时期有机质的富集和保存。中二叠统烃源岩主要发育于栖霞组(特别是下部),形成于碳酸盐台地内部凹陷(或盆地)。有机质的丰度随着地层旋回性变化而相应变化,所以海平面波动所诱导的生物产率变化是造成有机质富集的最主要控制因素,而不同级次海平面上升(海侵)叠加期是最有利的有机质富集期。上二叠统烃源岩主要赋存于大隆组(或相当地层),也形成于碳酸盐台内凹陷(或盆地)。此期有机质的富集与极度缺氧(甚至硫化)海水有关。On Yangtze block, there are three regionally-distributed high-quality source rock horizons： the Lower Cambrian, Upper Ordovician-Lower Silurian and Permian （Middle and Upper Permian）. The Lower Cambrian source rocks mainly consist of the lower black chert（Liuchapo Formation） and upper siliceous shales, carbonaceous shales （ or stone coals） （ Niutitang Formation）. During the Early Cambrian, extensive hydrothermal activities occurred on the Yangtze platform margins extending ca. 2 000 -3 000 km long, and released vast amounts of silica-rich fluids into the ocean, inducing extensive silica precipitation off the platform margin through basin. Simultaneously,a large quantity of H2S and greenhouse gases（ CO2, CH4 ）and metalliferous anoxic fluids were vented into oceanic waters and atmosphere, leading to an apparent elevation of atmospheric CO2 concentration and large-scale rise of sea-level. In this case,nutrient-rich deep water masses were carried through the upwelling currents into the shallower shelf,where the primary productivity was increased, which aggravated the anoxic state of water masses and enhanced the organic burial and preservation. The Upper Ordovician-Lower Silurian source rocks mainly comprise black shales and siliceous shales of Wufeng and Longmaxi formations,which formed during marine transgressions under a warm climate during the transitional time. With the accelerated amalgamation between Yangtze and Cathaysian blocks to the east,a large epicontinental sea with subbasins（ or sags） linked to a largely increased landmass was developed on the Yangtze Block, forming silled subbasins within which water circulation was restricted and oceanic stratification was intensified, favorable for organic accumulation. The enhanced chemical weathering could have increased nutrient flux into the basins, thereby increasing the primary productivity. However, greatly increased continental clastic flux into basins could have diluted the organic matters in sediments as seen in the upper part o

关 键 词：古生界烃源岩扬子地块 热液活动 海洋缺氧 原始生物产率有机质富集 

分 类 号：P534.4[天文地球—古生物学与地层学] P542[天文地球—地质学]