火山喷发间歇期沉积岩层古沉积环境的地球化学示踪与判别

Geochemical Tracing and Discrimination of Paleosedimentary Environment of Sedimentary Rock Intercalation During Volcanic Eruption Intervals

火山喷发堆积保存期古地理环境(陆上、水下)是影响火山岩油气储层发育的关键因素之一。基于火山喷发间歇期薄层沉积岩层具有沉积特征,其蕴含的微量元素地球化学特征与沉积期的氧化-还原环境密切相关,对古地理环境具有重要的指示意义。因此,通过火山喷发间歇期薄层沉积岩层岩心微量元素分析,可间接判断同一地质时期火山岩的堆积保存古地理环境(陆上、水下)。以新疆三塘湖盆地马朗凹陷上石炭统哈尔加乌组火山喷发间歇期薄层泥岩、粉砂岩等沉积岩层为实例,通过泥岩、粉砂岩等岩心主、微量元素分析,采用总结归纳的U/Th、自生U、V/Cr、Ni/Co、V/Sc、V/(V+Ni)、Cu/Zn、Fe^(3+)/Fe^(2+)、Sr/Ba、V/Zr和B/Ga等11项用以示踪判识细粒沉积物沉积古环境的主、微量元素地球化学参数图版标准,判断哈尔加乌组火山喷发间歇期沉积岩层沉积期的氧化-还原环境,从中推断哈尔加乌组火山岩喷发堆积保存时的古地理环境(陆上、水下)信息。对哈尔加乌组火山喷发间歇期泥岩、炭质泥岩和粉砂岩在纵向上演化特征类似的V/(V+Ni)、V/Sc、Sr/Ba、V/Cr、V/Zr、Cu/Zn和B/Ga等7类微量元素地球化学参数指标研究表明,泥岩、炭质泥岩和粉砂岩等沉积岩层主要沉积于水下还原环境以及滨浅湖频繁水、陆过渡环境;推断与其同一地质时期的火山岩主要喷发堆积保存于水下环境,也存在频繁水、陆过渡复杂沉积成因环境。

The paleosedimentary environment during the preservation of volcanic materials is one of the key factors influencing the volcanic oil-gas reservoir.During the interval of volcanic eruption,the deposited thin sedimentary lithologic layer has sedimentary characteristics.The trace elemental characteristics in the thin sedimentary layers are closed related to the paleosedimentary oxide-reductive environment and are important parameters for paleoenvironment identification.Thus,the paleosedimentary environment can be identified indirectly based on the trace element analysis on cores of the thin sedimentary layers during volcanic eruption intervals.Thin sedimentary lithologic layers,including mudstone and siltstone,had deposited during the interval of volcanic eruption in the Upper Carboniferous Haerjiawu Formation of Malang sag,Santanghu basin,Xinjiang.Eleven types of trace element ratios of these fine sediments,including U/Th,authigenic U,V/Cr,Ni/Co,V/Sc,V/(V+Ni),Cu/Zn,Fe^(3+)/Fe^(2+),Sr/Ba,V/Zr,and B/Ga are used to trace the oxide-reductive paleoenvironment during the interval of volcanic eruption.Seven kinds of parameters,V/(V+Ni),V/Sc,Sr/Ba,V/Cr,V/Zr,Cu/Zn and B/Ga of mudstone,carbon mudstone,and siltstone indicate an underwater reduction environment and the coastal shallow sea environment with frequent water-land transition;It is concluded that the volcanic rocks of the Haerjiawu Formation are mainly deposited by eruption and preserved in underwater environment,and the complex sedimentary genetic environment of frequent water-land transition also exists.