宁镇地区五峰组-高家边组页岩U-Mo协变模式与古海盆水体滞留程度

U-Mo covariance model of Wufeng-Gaojiabian Formation marine shale in Ningjing-Zhenjiang area and its implication for water retention degree in ancient sea basin

通过对下扬子的宁镇地区SY1井五峰组-高家边组页岩U、Mo元素和有机质含量的地球化学分析,探讨在还原环境下痕量元素富集特征与水体滞留情况的对应关系。通过Mo-TOC和U-Mo协变模式研究表明:五峰组沉积时期尽管海平面降低,但强烈的滞留海盆环境使得水体交换速率缓慢,降低有机质的消耗,形成了利于有机质保存的缺氧环境;高家边组沉积时期海盆的滞留程度明显弱于五峰组沉积时期,但由于志留纪早期受全球性海侵事件影响,海平面快速上升触发上升流,促进了生物复苏、提高了海洋表层生产力,进而加强和维持了底部水体的还原环境,导致海底进一步缺氧是高家边组第一段有机质富集和保存的关键因素。高家边组底部是下扬子地区页岩气的有利目标层。

The correlation between trace element enrichment and water retention in reduced environment was studied on the basis of the geochemical analysis of U and Mo trace elements and organic matter contents in the Wufeng-Gaojiabian Formation shale in Well SY1.Analysis of covariant model of Mo-TOC and U-Mo showed that,despite the decrease of sea level in the sedimentary period of the Wufeng Formation,the strong stagnant basin environment made the water exchange rate slow and reduced the consumption of organic matter,forming an anoxic environment conducive to the preservation of organic matter.The extent of basin retention of Gaojiabian Formation depositional period was significantly weaker than that of Wufeng Formation depositional period,but as a result of the global marine transgression events in early Silurian,rapid rise in sea level triggered upwelling,promoted the biological recovery,enhanced the ocean surface productivity,as well as enhanced and maintained the water at the bottom of the reductive environment.The lack of oxygen at the bottom of the sea was the key to the enrichment and preservation of organic matters of the 1st Member of Gaojiabian Formation.Therefore,the lower part of the Gaojiabian Formation is a favorable target for shale gas exploration in the lower Yangtze region.