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在扬子板块北缘城口明中剖面及巫溪徐家坝剖面下志留统龙马溪组底部的硅质岩、泥岩中发现椭球状重晶石结核。其矿物组成主要为重晶石颗粒与作为“基质”的黄铁矿、粘土矿物和石英。通过重晶石岩石学、矿物学及锶同位素分析表明,重晶石结核形成于早期成岩阶段松软沉积物的孔隙水中。上升洋流带来丰富的营养及富钡物质,表层海水的高初始生产力促使生物繁盛,海水中的钡通过生物作用富集形成生物钡,生物钡(bio-barite)在埋藏过程中的硫酸盐耗竭区(sulfate depleted zones)通过硫酸盐细菌作用(BSR)溶解被激活提供了钡的来源。围岩岩性(黑色泥岩和硅质泥岩)表明重晶石结核形成于缺氧的环境中。上述研究对深入理解早志留世时期扬子板块北缘古海洋环境有一定的启示作用。
Ellipsoidal barite tuberculosis was found in the chert of the Mingkou section of the mouth of the Chengtou in the northern margin of the Yangtze Plate and the siliceous rocks and mudstones at the bottom of the Longmaxi Formation of the Silurian in the Xujiaba section of Wuxi. Its mineral composition is mainly barite particles with pyrite, clay minerals and quartz as the “matrix”. Barite petrology, mineralogy and strontium isotope analysis indicate that barite nodules formed in the pore water of soft sediments in the early diagenetic stage. The rising ocean currents bring abundant nutrients and barium-rich substances. The high initial productivity of the surface seawater promotes the flourishing of organisms. The barium in the seawater is biologically enriched to form bio-barium, and the bio-barite depletes the sulfate during the burial process Sulfide depleted zones provide a source of barium through activation by sulfate bacterium (BSR) lysis. Surrounding rock lithology (black mudstone and siliceous mudstone) indicates that barite nodules are formed in anoxic environments. The above studies have some enlightenment on understanding the ancient marine environment in the northern margin of the Yangtze Plate during the Early Silurian.