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埃迪卡拉纪-寒武纪重要地质历史转折时期全球多陆块广泛沉积硅质岩。塔里木盆地西北缘下寒武统玉尔吐斯组底部10所发育的薄层状硅质岩,以富含残余颗粒、磷质结核和重晶石结核而显得非常特殊和罕见,明显有别于国内外报道的常规硅质岩。为了揭示该套硅质岩的成因及沉积模式,通过剖面测量(库勒剖面)、薄片鉴定、SEM观察、能谱探针、主微量元素特征、氧硅同位素分布等岩石学-地球化学分析方法,认为玉尔吐斯组硅质岩垂向上共分五小段,其主要矿物成分是石英、白云石,自生矿物主要有重晶石、方沸石、黄铁矿等,不同硅质岩段微观结构显示出十分明显的组构变化,包含残余颗粒结构、残余晶粒结构、隐晶质结构和微晶结构。所测剖面硅质岩沉积于靠近大陆/古隆起的高盐度浅海陆架(高Al2O3/(Al2O3+Fe2O3)比值,高Mg O/Al2O3比值),其陆源碎屑主要来自大陆地壳或基底花岗岩的风化产物,并且受到Si O2的稀释作用影响(Th/Ti与Al/Ti关系)。氧化还原敏感元素(如Ba、V、Ni、Cu、Zn、U等)不同程度的富集及氧化还原指标(V/Cr介于0.81~8.34)特征,表明硅质岩段沉积早期处于氧化环境,水体能量较强,显微镜下见圆度较好的内碎屑颗粒、微生物席碎片;中晚期经历了水体循环不畅的有氧/缺氧分层环境(Ce/Ce*负异常),显微镜下微生物球粒、粪球粒、浮游藻(粘结)团块发育,有机质含量较高(TOC可达2%以上)。稀土元素特征(低∑REE、中等Ce负异常、显著的Y正异常和Eu正异常)以及δ30Si和δ18O20值分布范围暗示硅质岩地球化学特征主要继承自热液流体和海水,受陆源碎屑影响较弱。自近台内裂陷中心上升的富含多金属的富硅热液以及陆源碎屑提供大量营养,为微生物大繁盛和硅质的富集成矿奠定物质基础?水体中硅的溶解度降低(温度降低、p H降低和水体盐度升高)促使硅质胶体颗粒化学沉淀,而微生物(特别是嗜热微生物)的新陈代谢活动往往加速了这一过程。
Edith Calanji - Cambrian important geological history turning point Multi-block global deposition of silicalite. Ten thin layers of siliceous rocks developed at the bottom of the Lower Cambrian Yulteasi Formation in the northwestern margin of the Tarim Basin are very special and rare with abundant particles of residual particles, phosphorus and tuberculosis and distinctly different from those at home and abroad Reported conventional silicalite. In order to reveal the genesis and sedimentary model of this set of cherts, the petrologic-geochemical analysis methods such as profile measurement (Culer section), slice identification, SEM observation, energy spectrum probe, main and trace element characteristics, , The authors believe that the Yertu Tu Si group is vertically divided into five subdivisions. The main mineral components are quartz and dolomite. The main authigenic minerals are barite, analcime and pyrite, and the microstructures of different siliceous rocks are shown A very obvious structural change, including residual grain structure, residual grain structure, cryptocrystalline structure and microcrystalline structure. The measured profiles of silicalite deposited on high salinity shallow sea shelf (high Al2O3 / (Al2O3 + Fe2O3) ratio, high MgO / Al2O3 ratio) near the continental / paleohighs, and the terrigenous detritus mainly comes from continental crust or basement granite Weathering products, and are affected by the dilution of Si O2 (Th / Ti vs. Al / Ti relationship). The enrichment of redox-sensitive elements (such as Ba, V, Ni, Cu, Zn, U, etc.) and the redox indicators (V / Cr ranged from 0.81 to 8.34) indicate that the early stage of deposition of siliceous rocks is in an oxidizing environment , The water body energy is stronger, the inner round debris particles and microbiological fragments are seen better under the microscope; the late oxygen and oxygen environment (Ce / Ce * negative anomaly) Lower microbial pellets, pelleted pellets, phytoplankton (bond) mass development, high organic matter content (TOC up to 2% or more). REE characteristics (low ΣREE, moderate negative Ce, significant positive Y anomalies and positive Eu anomalies) and δ30Si and δ18O20 values suggest that the geochemical characteristics of the cherts are mainly derived from hydrothermal fluids and seawater, Weak influence. Rich in polymetallic-rich silicate-rich hydrothermal fluids and terrigenous debris rising up near the intracontinental rift center provide substantial nutrients for the generous microbial enrichment and siliceous mineralization. The solubility of silicon in water decreases (temperature decreases , P H decreases and salinity of the water body increases) causes the silical colloidal particles to precipitate chemically, and the metabolic activity of microorganisms, especially thermophilic microorganisms, tends to accelerate the process.