新疆若羌县红柳沟Ⅰ号剖面新元古界成冰系冰沟南组硅质岩特征与沉积环境*

新疆若羌县红柳沟Ⅰ号剖面出露厚约300 m的新元古界成冰系冰沟南组的细粒沉积物和碳酸盐岩等,并发现有沥青油气显示。通过厚160 m左右硅质岩剖面实测以及岩石学、地球化学等研究表明: 红柳沟Ⅰ号剖面中的硅质岩主要由石英、黏土构成,有微量的含铁、锰、磷的独立矿物;具有隐晶质、微晶石英和粗-巨晶石英“镶嵌结构”3种结构类型;硅质岩中SiO₂、Fe₂O₃、Ba和δEu_n值相对较高,Al₂O₃、MnO、MnO/TiO₂、U/Th和Sr/Ba值较低,∑REE、Sr/Ba、MnO₂/TiO₂和δCe_n值等呈现有规律的变化;δ³⁰Si值平均为-0.43‰(-0.8‰~0.3‰),$\delta^{18}O_{Snow}$值平均为20.42‰(16.0‰~26.0‰),估算的平均温度为90 ℃(52~127 ℃),指示了硅质岩具有多个沉积旋回,在海水与热水参与的大陆边缘盆地中沉积,并经历了早成岩期、浅埋藏期以及与多期走滑断裂活动有关的热流体与大气淡水的叠加改造。

Characteristics and sedimentary environment of siliceous rock in the Neoproterozoic Cryogenian Binggounan Formation at Hongliugou section Ⅰ in Ruoqiang County,Xinjiang

The fine-grained sediments and carbonate rocks with a thickness of 300 m are discovered at the Binggounan Formation of Neoproterozoic Cryogenian system in Hongliugou section Ⅰ of Altyn in Xinjiang,and the asphalt which is the indicator of oil and gas is also found. Based on the section measurement,petrology and geochemistry of the 160 m thickness of siliceous rocks,it shows that siliceous rocks in the profile are mainly composed of quartz,clay,and tiny amounts of iron,manganese and phosphorus-bearing independent minerals. It has three types of structures,including cryptocrystalline,microcrystalline quartz and coarse-megacrystalline quartz with a “mosaic structure”. The concents of SiO₂,Fe₂O₃,Ba and δEu_n in siliceous rocks are relatively high,while the contents of Al₂O₃,MnO,MnO/TiO₂,U/Th, Sr/Ba are much lower. The values of ∑REE,Sr/Ba,MnO₂/TiO₂ and δCe_n change regularly. The average δ³⁰Si is -0.43‰(-0.8‰~0.3‰),and the average $\delta^{18}O_{Snow}$ is 20.42‰(16.0‰~26.0‰),and the estimated average temperature is 90 ℃(52~127 ℃),which indicates that there are multiple sedimentary cycles for the siliceous rocks. They deposit in the continental margin basin that is characterized as the mixing of sea water and hydrothermal fluid. Afterwards,they underwent the early diagenesis,shallow burial period,the superimposition and reworking of thermal and fresh water related with the multiple strike slipping activities.