四川盆地早寒武世裂陷槽西部页岩发育背景与有机质富集

四川盆地绵竹-长宁裂陷槽内部发育潜力巨大的下寒武统烃源岩。对位于裂陷槽西部中央的错巴沟剖面下寒武统页岩开展了总有机碳(TOC)、矿物组成和主、微量元素测试,以揭示其发育时期的构造背景、陆源输入、古气候、初级生产力、水体氧化还原条件与热液活动等与有机质富集之间的关系。结果表明研究区主要处于被动大陆边缘沉积环境,具有较稳定的沉积速率,气候温暖湿润,存在间歇性气候变冷。TOC值分布在5.96%~23.15%之间,平均含量为11.64%。营养元素P、Ba、Cu和Ni等揭示了该时期高的初级生产力,这是因为温暖湿润的气候加剧了化学风化,从而向海洋输入大量的营养物质导致的。氧化还原敏感元素指标与黄铁矿含量说明研究区Ⅱ段、Ⅲ段富有机质沉积物主要发育于厌氧硫化的底水环境。下寒武统异常富集的微量金属元素可能与早寒武世裂陷槽拉张背景下的海底热液活动有关,其不仅可促进化能自养型生物的发育,同时与海水混合后有利于底水厌氧硫化环境的形成,促进有机质的保存。

The development setting and the organic matter enrichment of the Lower Cambrian shales from the western rift trough in Sichuan Basin

The Mianzhu-Changning rift trough has great potential for the development of the Lower Cambrian source rock. Total organic carbon(TOC),mineral composition,major and trace elements of the Lower Cambrian shales in the central part of the rift trough were measured to reveal the relationship between the tectonic setting,terrigenous input,paleoclimate,primary productivity,redox conditions as well as the hydrothermal activity and the enrichment of organic matter during its development period. The results show that the study area is located in the passive continental margin sedimentary environment,with stable sedimentary rate,warm and humid climate alternated by intermittent climate cooling. The TOC values range from 5.96% to 23.15% with an average content of 11.64%. Nutrient elements of P,Ba,Cu and Ni reveal the high primary productivity during this period,which is due to the increased chemical weathering caused by warm and humid climate,thus importing large amounts of nutrients into the ocean. The index of redox sensitive elements and the content of pyrite indicate that the organic-rich sediments in the second and third stages are mainly developed in the bottom water environment of anaerobic sulfurization. The abnormal enrichment of trace metals may be related to the hydrothermal activity from the seabed under the stretching background in rift during the Early Cambrian,which not only provides material for the flourishing of anaerobic chemoautotrophs,but also facilitates the formation of anaerobic sulfurization environment in the bottom water and promotes the preservation of organic matter after mixing with seawater.