川东北地区下志留统龙马溪组上升洋流相页岩沉积特征

上升洋流相是海相富有机质页岩的重要沉积模式。依据川东北巫溪地区下志留统龙马溪组露头和钻井资料，对埃隆阶富有机质页岩开展了精细表征，初步认为巫溪地区埃隆阶显示出具有受上升洋流控制的沉积建造特征，并形成了4点认识：①岩性组合多样，自下而上出现厚层状碳质页岩夹硅质页岩、碳质页岩夹高自然伽马（GR为185~203 cps）砂岩层、碳质页岩和黏土质页岩夹重晶石团块、黏土质页岩与高自然伽马砂岩层韵律层、厚层-块状黏土质页岩等多种深水岩相组合，较五峰组-鲁丹阶复杂。②具有低S/C值、高Mo含量，显示埃隆阶沉积期巫溪海域拥有低盐度、弱封闭的大陆边缘特征。③P、Fe、Ba等营养物质含量丰富，显示巫溪海域古生产力在奥陶纪和志留纪之交普遍较高，并在埃隆阶沉积期达到高峰，且明显高于同期台盆区。④沉积速率总体较快，大致呈现初期慢、中晚期快的特点，在埃隆阶沉积中期以后达到25.24~149.42m/Ma，并控制形成厚18~50 m、TOC为2%~4%的富有机质页岩。由此判断，扬子海盆龙马溪组富有机质页岩除主体为静水陆棚相缓慢沉积外，在台盆区北缘埃隆阶及以上存在上升洋流相沉积。

Sedimentary characteristics of upwelling facies shale in Lower Silurian Longmaxi Formation,northeast Sichuan area

The upwelling facies is an important sedimentary model of marine organic-rich shale. Based on the outcrop and drilling data of Lower Silurian Longmaxi Formation, Wuxi area, Northeast Sichuan, a fine characterization is made on the Aeronian organic-rich shale. It is preliminarily concluded that the Aeronian shows the sedimentary formation characteristics controlled by upwelling, and four understandings are achieved as follows:(1)The lithological assemblages are diversified, presenting multiple deep lithofacies assemblages of the thick-layer carbonaceous shale with interbedded siliceous shale, carbonaceous shale with a high gamma sandstone layer (GR 185-203 cps), carbonaceous and clayey shales with barite lumps, rhythmic layers composed of clayey shale and high gamma sandstone layer, and thick-massive clayey shale from bottom to top, more complex than Wufeng-Rhuddian Formations. (2)Low S/C ratio and high Mo content indicate that the Wuxi sea area in the Aeronian sedimentary period has continental margin characteristics with low salinity and low enclosure. (3)The rich nutrients such as P, Fe and Ba show that the paleoproductivity of Wuxi sea area was generally high through the Ordovician and Silurian transition and peaked at the Aeronian, significantly higher than contemporaneous basin area. (4)The deposition rate was relatively fast, roughly characterized by being slow in early stage and quick in middle-late stage, reaching 25.24-149.42 m/Ma after the middle Aeronian sedimentary period and controlling the formation of organic-rich shale with the thickness of 18-50 m and TOC of 2%-4%. Therefore, it can be judged that the organic-rich shale in Longmaxi Formation of Yangtze sea basin is dominated by slow deposition of stagnant water shelf facies, and the Aeronian on the northern margin of basin area and above is the upwelling facies sediment.