塔里木盆地早寒武世风化—热液耦合过程及其地质意义

Coupled weathering-hydrothermal process and its geological significance during the Early Cambrian in the Tarim Basin

以塔西北下寒武统玉尔吐斯组黑色页岩为例,利用总有机碳(TOC)、热解、干酪根碳同位素、主量元素、微量元素及稀土元素等测试分析,探讨风化作用、热液活动及其对有机质富集的影响。结果表明:风化—热液耦合过程促进下寒武统富有机质页岩的发育。古风化作用为海洋生物生长提供必需的营养元素(Fe)和丰富的陆源碎屑,前者导致浮游生物的勃发,后者促进水体有机质的吸附和沉降,为有机质富集奠定物质基础;热液活动提供丰富的还原性气体(H_(2)S)和热液硅,前者创造硫化缺氧的沉积环境及透光厌氧带,促进沉积有机质的保存,后者稀释沉积有机质的丰度。当风化作用较强而热液活动较弱时,古生产力勃发,热液硅稀释作用较弱,促进黑色富有机质页岩的发育;当热液活动较强而风化作用较弱时,古生产力受限,热液硅稀释作用较强,导致相对贫有机质硅质页岩的形成。塔西北下寒武统烃源岩的发育模式受风化—热液协同控制。芳基类异戊二烯烃的油源对比显示,风化—热液耦合控制下发育的富有机质烃源岩对塔里木盆地丰富的深层油气资源具有重要贡献。该结果对塔里木盆地深层油气勘探具有参考意义。

Samples from the Lower Cambrian Yuertusi Formation black rock series in the Northwest Tarim Basin were analyzed for total organic carbon(TOC),rock-eval,carbon isotope of kerogen,major and trace elements,and rare elements,aiming at discussing the paleo-weathering,hydrothermal activity,and their influence on organic matter(OM)enrichment.Results show that the coupled process of weathering and hydrothermal promoted the organic-rich shale's deposition in the Lower Cambrian.Abundant teleorganic nutrients(Fe)and terrigenous clastics carried into the sea by the paleo-weathering induced plankton blooms and promoted the adsorption and sunk of OM in water,respectively,which laid a material foundation for the formation of organic-rich source rocks.Hydrothermal activity brought abundant reducing gases(H_(2)S)and hydrothermal silicon into the sea.The former triggered a sulfur-anoxic sedimentary environment and photic zone euxinia,which enhanced the preservation of sedimentary OM.However,the latter might dilute the abundance of sedimentary OM to some extent,resulting in the relatively organic-poor siliceous shale rocks.During the period of strong paleo-weathering and weak hydrothermal activity,the paleo-productivity was high while the hydrothermal silicon dilution was negligible,which promoted the development of black organic-rich shales.During the period of intense hydrothermal activity and weak paleo-weathering,the paleo-productivity was limited,while the hydrothermal silicon dilution was remarkable,which led to the development of organic-poor siliceous shales.As a result,the development of the Lower Cambrian source rocks in the Northwest Tarim Basin was controlled by the coupled weathering-hydrothermal process.Additionally,the oil-source correlation based on aryl isoprenoids indicated that the source rocks developed under this coupled process had remarkable contributions to the Tarim Basin's abundant hydrocarbon resources.It will be of great reference value for future deep petroleum exploration in the Tarim Basin.