深部流体在富有机质烃源岩形成中的作用

The role of deep fluid in the formation of organic-rich source rocks

长期以来,关于富有机质烃源岩形成的研究主要集中于盆地之内,盆地之外流体活动对富有机质烃源岩形成的影响关注较少。深部流体作为联系沉积盆地内、外的纽带,通过提高海洋初级生产力和形成有利的有机质保存环境2个方面作用为富有机质烃源岩的形成创造条件。生产力方面,深部流体携带了大量NO_3^-、PO_4^(3-)、NH_4^+等营养盐类,CH_4、CO_2、H_2、NH_3等热液气体和Fe、Mn、Zn、Co、Cu等微量金属元素以及来自地球内部的古细菌、嗜热细菌等微生物,它的注入促进了水体生物的繁盛和初级生产力的提高,为有机质的形成和富集创造了条件。保存环境方面,深部流体的喷发,向大气和海洋中输送了大量的CO_2,与水体中的Ca^(2+)、Mg^(2+)等离子结合,形成碳酸盐类,增加了水体的盐度,促进了水体的分层和海水循环的静止,为海洋环境中有机质的富集创造了有利的水体动力学条件和氧化还原状态。而岩浆热液活动向大气和海洋输送的大量H_2S、CO等还原性气体溶解于水中,同样可以促进水体还原环境的形成。因此,深部流体的喷发为富有机质烃源岩的形成提供了重要物质保障和有利的环境条件。

For a long time,the research of the formation of organic-rich source rocks has mainly focused on the inner basins.The effect of exogenous fluid on organic-rich source rocks’formation has received little concern.As the belt connecting the inner and external of a basin,deep fluid created proper condition for the formation of organic-rich source rocks,by promoting primary productivity and organic preservation.In productivity facet,deep fluid carried a large amount of nutrient such as NO3^-,PO4^3-and NH4^＋,hydrothermal gases such as CH4,CO2,H2and NH3,trace metal elements such as Fe,Mn,Zn,Co and C,as well as microbes from deep earth such as archaea bacteria and thermophilic bacteria.The injection of deep fluid not only promoted the thriving of organism and primary productivity,but also provided favorable conditions for organic formation and enrichment.In preservation facet,the eruption of deep fluid sent massive CO2to atmosphere and ocean.By combining with ions like Ca^2＋and Mg^2＋,these CO2transformed into carbonate.As a result,it increased the salinity of water,which in return lead to the stratification and quiescence of water.All of above process created advantageous hydrodynamic condition and redox state for organic enrichment.Besides,the dissolution of reductive gas from magma and hydrothermal,such as H2S and CO,also contributed to the formation of reductive water condition.To sum up,the eruption of deep fluids provided significant ingredients sources and favorable preservation condition for the formation of organic-rich source rocks.