摘要：

鄂尔多斯盆地西缘斜坡相沉积是海相烃源岩的有利发育区。本文从元素地球化学入手，结合岩石、古生态特征，通过不同地区、不同层位元素赋存与迁移规律、沉积水体的变化及氧化－还原条件的分析，系统探讨了该区奥陶系元素地球化学与沉积环境、烃源岩分布及海底热流体活动的关系。认为水体深度、还原性、生物量及海底热流体的存在是海相生烃岩发育的重要条件。西缘北段桌子山组及南段三道沟组等台地相沉积及其以下地层，其沉积水体浅、开阔，还原性差，使有机质难以保存，不利于生烃岩的发育；而北段克里摩里组、乌拉力克组及南段的平凉组第一段等斜坡相沉积，其水体深而闭塞，还原性强，并且存在海底热流体活动，可形成有机质丰度较高的海相生烃岩。从而为评价该区奥陶系天然气成藏条件，提供了地球化学依据。

Abstract:

Clinothem slope facies is very advantageous to development of source rock of marine facies in the western margin of Ordos BasinAccording to the element geochemical characteristics，the relationships between element geochemistry and sedimentary environment，and the relationships between the distribution of source rock and heatflow of oceanfloor are discussed in this article by the numbers through analyzing the rules of element concentrate and transference and the change of sedimentary water mass and oxidationreduction condition on the different horizons and the different areasThe conclusion is that water mass depth and reduction and biocoenosis and the heatflow of oceanfloor are very important to the development of source rocksIn the Zhuozishan Formation on the north of the western margin and Sandaogou Formation on the south of the western margin，the preservation of organism is very difficult，because during their deposition，the  water mass was very shallow and widen，and the reduction was weakIn the Kelimoli Formation and Wulalike Formation on the north of western margin and the first section of Pingliang Formation on the south of the western margin，the abundance of organism is very high，because during their deposition the  water mass was very occlusive and the reduction was very strong，also heatflow of the ocean floor was very activeThese analyses provide the basement of element geochemical characteristic for evaluating the reservoir of the gas