本文为国家自然科学基金项目(编号41802173)和中国地质调查项目(编号DD20221674, DD20230042, DD20230311)联合资助的成果
埃迪卡拉纪—寒武纪转折期是地质历史上的关键期，全球范围内普遍发育一套黑色岩系，包括硅质岩、泥岩和白云岩。在这套黑色岩系中下部，发育了不同厚度的硅质岩，尤其是在塔里木盆地西北缘，黑白燧石条带韵律性互层且硅质岩分布变化大，其成因对寒武系玉尔吐斯组优质烃源岩形成环境具有重要指示意义。本文以塔西北地区新柯地1井这套黑色岩系中硅质岩为研究对象，运用岩芯观察、镜下薄片鉴定、主微量元素和稀土元素分析，研究硅质岩与有机质的成因及其二者之间的共生机理，硅质岩较高的Ti、V、Y、Ba等元素含量、较低的δ30Si值(1. 2‰~0. 7‰)、明显的Ce负异常说明其硅质流体为热液来源，但是硅质岩不是热液脉体侵入形成，而是富含硅质的流体与冰冷的海水混合沉积而成，硅质岩沉积受温度、pH值、有机质等因素共同控制，有机质的存在可以促进硅质沉淀。同时系统地研究了黑白燧石条带韵律性互层的成因，白色层由纯的微晶石英组成，而黑色层由碎屑碳质颗粒、石英颗粒和碳质纹层组成，认为是微生物席活动的结果，硅质岩中黑白燧石层受冰期和间冰期控制。硅质岩中较高的Al2O3/(Al2O3+Fe2O3)比值和较低的Lan/Cen比值代表受陆源影响的大陆边缘沉积环境，结合古气候、海平面变化等信息，认为塔西北地区寒武系玉尔吐斯组硅质岩以及硅质页岩沉积于局限海湾或潟湖环境，为正确认识硅质页岩的形成环境和烃源岩的评价预测提供理论指导。
The Ediacaran- Cambrian transition is a crucial interval in the geological timeline, marked by the widespread occurrence of various black rock series worldwide, such as siliceous rock, mudstone, and dolomite. In the northwest region of the Tarim basin, specifically within the middle and lower sections of the black series, there is a notable presence of siliceous rocks. These rocks exhibit alternating black and white chert bands, displaying diverse distribution patterns. Determining the origin of these siliceous rocks is essential for understanding the environment conducive to high- quality source rocks within the Yuertusi Formation. In this study, we focus on investigating the siliceous rock within the black rock series of well Xinkedi 1. By employing field observations, petrological analysis, and geochemical techniques, we aim to unravel the origin of these siliceous rocks and their relationship with the organic matter present within the sequence. Additionally, we systematically examine the processes responsible for the formation of the black and white chert bands. The white layers are predominantly composed of pure microquartz, while the black layers contain a mixture of detrital carbonaceous matter, quartz grains, and carbonaceous microlaminae, which are interpreted as remnants of microbial mats. These variations in coloration are believed to be influenced by glacial and interglacial periods. We also establish that the occurrence of organic matter is conducive to the formation of silica. The higher Al2O3/(Al2O3+Fe2O3) ratio and lower Lan/Cen valuesuggest a deposition environment dominantly influenced by terrigenous sources in a continental margin. Furthermore, considering paleoclimate and sea level fluctuations, it can be inferred that the deposition of siliceous rock and siliceous shale primarily took place in confined bay or lagoon environments. This study provides valuable insights into understanding the formation environment of siliceous shale and contributes to the evaluation and prediction of source rocks, offering practical implications for resource exploration and development.
LIU Lihong, GAO Yongjin, ZHU Guangyou, YANG Youxing, YIN Chengming, SUN Xiangcan, LI Qingyao.2024. Genesis of siliceous rock in the black rock series of Ediacaran- Cambrian transition and its environmental significance in northwestern Tarim basin[J]. Acta Geologica Sinica,98(2):511-529.