湖北鹤峰地区二叠系大隆组黑色岩系成因——来自鹤地1井的元素地球化学证据

Genesis of black rock series of Upper Permian Dalong Formation in Hefeng area,Hubei province:an evidence from the analysis of element geochemistry in Well HD1

为明确湖北鹤峰地区二叠系大隆组的沉积环境特征及黑色岩系的成因,开展了鹤地1井黑色岩系详细的元素地球化学分析。结果表明,大隆组缺氧的还原环境控制了有机质的富集,其早期沉积环境相对较稳定,为贫氧且富含H2S的还原环境,而中—晚期则呈明显波动变化的贫氧—缺氧环境。大隆组沉积期上升流的发育提供了大量的富营养物质,导致沉积水体缺氧,产生较高的古生产力。与同生断裂有关的热水上涌主要造成自生白云石和钠长石形成、硅质生物溶蚀再胶结作用,促使有机质发生热演化,对页岩气无不利影响。大隆组局部发育的层状硅质岩具有生物成因和自生化学沉淀成因2种类型。

To identify the sedimentary environment characteristics and the genesis of black rocks in Upper Permian Dalong Formation, Hefeng area, Hubei province, the detailed element geochemistry of black rocks was analyzed in Well HD1. The results show that the reducing environment of Dalong Formation is the key control factor of organic matter enrichment. The early sedimentary was relatively stable as the reducing environment with lean oxygen and rich H2S, while the mid-late sedimentary presented the oxygen lean-oxygen deficit environment with significant fluctuations. In the sedimentary period of Dalong Formation, the upwelling development provided a lot of nutrient-rich materials, leading to the oxygen deficit environment in sedimentary water mass and the high paleo-productivity. The upwelling of thermal water along the contemporaneous faults had no adverse effect on the development of shale gas, which mainly caused the formation of authigenic dolomite and albite, the dissolution and re-cementation of siliceous organisms and the promotion of thermal evolution on organic matters. The layered silicalite locally developed in Dalong Formation are of two genetic types, i.e., biological genesis and authigenic chemical precipitation.