鄂尔多斯盆地三叠系延长组黑色岩系成因探讨——以铜川地区长73段为例

鄂尔多斯盆地三叠系延长组黑色岩系的成因一直存在争议。除传统认识的陆源物质沉积成因外,火山物质沉积和热水沉积逐渐得到关注和认可。选取盆地东南缘瑶曲衣食村长7₃段野外露头剖面,进行系统观察和无间距采样,并借助显微镜、X衍射、电子探针等分析方法对黑色岩系沉积特点进行研究,结果显示:1）剖面中一部分的“黑色泥岩”和“粉-细砂岩”分别是尘凝灰岩和粉-细砂级凝灰岩,在纵向和横向上发育规模显著; 2）热水沉积产物丰富,包括水铵长石+黄钾铁矾+黄铁矿、重晶石+非晶质SiO₂、斜长石的钠长石化等矿物组合,它们与陆源碎屑沉积间互,受浅湖-半深湖相沉积、重力流沉积、远源火山碎屑沉积以及热液流体改造作用的共同控制。上述特殊成因的黑色岩系既可以成为优质烃源岩层,也可成为优质储集体,对于油气富集具有重要意义。

Genesis Analysis of Black Rock Series: A case study of Chang 73 member in Tongchuan area

The genesis of the black rock series of the Triassic Chang 7₃ member has been controversial. It is gradually gaining acceptance that pyroclastic deposition and hydrothermal deposition are the genesis,along with normal terrigenous sedimentation. In this study,of the Chang 7₃ member was sampled from top to bottom,and the samples were analyzed by SEM, XRD and optical microscopy to determine the sedimentary properties of the Yaoqu-Yishi village section in Tongchuan. It was found that(1) so-called "black mudstone" is dust tuff and "silt-fine sandstone" is silt to fine-sand tuff,and(2) hydrothermal deposition is abundant in the section,with typical hydrothermal mineral assemblages such as buddingtonite + jarosite + pyrite,amorphous SiO₂ + barite,and albitized plagioclase. Pyroclastic deposits and hydrothermal deposits are interbedded with normal terrigenous sediments from deposited semi-deep and shallow lake facies,gravity flow deposits,and massive pyroclastic deposits far from the eruption source,with modified hydrothermal fluid. This particular genesis and sedimentary setting makes the black rock series a potentially highquality hydrocarbon source rock and reservoir favoring significant hydrocarbon accumulation.