准噶尔盆地吉木萨尔凹陷二叠系芦草沟组沉积古环境与生物来源探讨

Discussion on the sedimentary paleoenvironment and biological source of Permian Lucaogou Formation in Jimusar Sag,Junggar Basin

火山—热液作用对准噶尔盆地吉木萨尔凹陷二叠系芦草沟组沉积演化与生物来源有重要影响。采集吉木萨尔凹陷J305井岩心样品,应用元素地球化学、有机地球化学方法进行包括烃源岩地球化学特征、沉积古环境演化及有机质生物来源在内的系统研究。结果表明:①芦草沟组烃源岩样品的主、微量元素在芦一段、芦二段之间呈现一定的差异,芦一段相对富集Sr、U、Fe_(2)O_(3)、MgO和CaO,芦二段则相对富集V、SiO_(2)和Al_(2)O_(3)。②芦草沟组沉积期整体处于偏咸化的水体环境,芦一段水体较深,芦二段水深波动大且相对较浅,从芦一段到芦二段,盐度逐渐降低;古氧相为相对稳定的还原环境,有机质富集受控于古生产力水平。③烃源岩有机质生物来源在一定程度上与古盐度、古气候及火山—热液活动有关,生物来源组成的总体特征为细菌和藻类的丰度大于高等植物,细菌的丰度大于藻类,藻类以绿藻为主,其中细菌中蓝细菌占有一定比例,且芦一段中蓝细菌占比相对较高。④芦草沟组的沉积演化可细分为5个阶段:干旱—半咸水阶段(芦一早期)→半干旱—咸水阶段(芦一中期)→干旱—半咸水阶段(芦一晚期)→湿润阶段(芦二早期,生物来源转变)→半干旱—微咸阶段(芦二晚期)。芦草沟组的沉积和生物来源受古环境的控制,火山—热液作用提供的大量营养物质,提高了古生产力水平,同时稳定的还原环境为有机质的保存提供了必要条件。

Volcano-hydrothermal effect has an important influence on the sedimentary evolution and biological source of Permian Lucaogou Formation in Jimusar Sag.The core samples of Well J305 in Jimusar Sag of Junggar Basin were collected and systematically studied by element geochemistry and organic geochemistry methods.The specific contents include geochemical characteristics of source rocks,evolution of sedimentary paleoenvironment and biological sources of organic matter.The results show that:(1)The major and trace elements in the source rock samples of the Lucaogou Formation show some differences between P_(2)l_(1) and P_(2)l_(2).The P_(2)l_(1) is relatively rich in Sr,U,Fe_(2)O_(3),MgO and CaO,and the P_(2)l_(2) is relatively rich in V,SiO_(2) and Al_(2)O_(3).(2)The sedimentary period of the Lucaogou Formation was generally in a saline water environment.The water body of the P2l1 was deep,and the water depth of the P_(2)l_(2) fluctuated greatly and was relatively shallow.From P_(2)l_(1) to P_(2)l_(2),the salinity gradually decreased.The paleo-oxygen phase is a relatively stable reducing environment,and the enrichment of organic matter is controlled by paleo-productivity,that is,biological source.Biological sources are related to paleosalinity,paleoclimate and volcanic-hydrothermal activities to a certain extent.(3)The overall characteristics of biological source composition are that the abundance of bacteria and algae is greater than that of higher plants,the abundance of bacteria is greater than that of algae,and algae are mainly green algae.Among them,cyanobacteria account for a certain proportion of bacteria,and the proportion of cyanobacteria in the P_(2)l_(1) is relatively high.(4)The sedimentary evolution of Lucaogou Formation can be divided into five stages:arid-brackish water stage→semi-arid-brackish water stage→arid-brackish water stage→humid stage→semi-arid-brackish water stage.The sedimentary and biological sources of the Lucaogou Formation are controlled by the paleoenvironment.Volcano-hydrothermal processes provide a large amount of nutrients and improve paleoproductivity.A stable reducing environment provides the necessary conditions for the preservation of organic matter.