鄂尔多斯盆地东北部侏罗系延安组漂白砂岩成因和古风化壳形成环境探讨

发布时间：2018-06-29 04:29

本文选题：漂白砂岩 + 不整合结构　；参考：《地质学报》2017年06期

【摘要】：鄂尔多斯盆地东北部侏罗系延安组顶部的砂岩漂白现象是油气运移逸散的重要证据,但前人仅从油气蚀变角度对漂白砂岩进行研究,而忽视了其形成地质环境。漂白砂岩分布在不整合面之下的风化壳中,指示不整合结构是其形成的重要地质背景。本文结合野外观察、矿物学和地球化学分析,对该区侏罗系不整合结构特征进行重点剖析,并对漂白砂岩成因进行探讨。结果表明,研究区侏罗系不整合风化黏土层不发育,不整合结构可划分为具半风化岩石和缺失半风化岩石两种类型。半风化层上部砂岩矿物成分以石英和高岭石为主,溶蚀孔隙发育,黑云母普遍发生高岭石化,砂岩中碱、碱土金属元素(K,Na,Ca,Mg)大量流失。半风化层下部砂岩钾长石含量偏高,黑云母不完全蚀变为水黑云母,砂岩中残留K和Mg。风化壳内细碎屑沉积岩物性条件差,与外部流体沟通有限,早期风化蚀变和后期烃类蚀变均较弱。漂白砂岩中的高岭石主要为风化淋滤的产物,砂岩因风化作用物性得以改善而成为重要的油气运移通道,同时富集铁氧化物而呈红色。风化壳内红色砂岩后期受到烃类的还原蚀变而发生褪色漂白,由于先后经历了风化淋滤和烃类还原两种蚀变作用,延安组顶部砂岩表现为胶结程度差、易遭受流水侵蚀的特性。碎屑岩古风化壳中的漂白现象是识别不整合结构参与油气运移成藏的重要标志。
[Abstract]:The phenomenon of sandstone bleaching at the top of Jurassic Yanan formation in northeastern Ordos Basin is an important evidence of oil and gas migration and dissipation. Bleached sandstone is distributed in the weathered crust below the unconformity surface, indicating that the unconformity structure is an important geological background for its formation. Combined with field observation, mineralogical and geochemical analysis, the unconformity structure characteristics of Jurassic in this area are analyzed emphatically, and the origin of bleached sandstone is discussed. The results show that the unconformable weathered clay layer of Jurassic in the study area is not developed and the unconformity structure can be divided into two types: the semi-weathered rock and the missing semi-weathered rock. The mineral composition of sandstone in the upper part of the semi-weathered layer is mainly composed of quartz and kaolinite, the dissolution pores are developed, kaolinite is generally occurred in kaolinite, alkali and alkali earth metal elements (K _ (Na) Na ~ (2 +) (mg) are largely lost in sandstone. The content of potassium feldspar in the sandstone of the lower part of the semi-weathered layer is high, the biotite is not completely eroded into hydrobiotite, and K and mg remain in the sandstone. The physical properties of fine clastic sedimentary rocks in weathering crust are poor, the communication with external fluids is limited, and the early weathering alteration and late hydrocarbon alteration are weak. The kaolinite in bleached sandstone is mainly the product of weathering and leaching. Because of the improvement of weathering physical properties, kaolinite becomes an important hydrocarbon migration channel and is red with the enrichment of iron oxides. The red sandstone in weathering crust is decolored and bleached by hydrocarbon reduction and alteration in late stage. Because of weathering leaching and hydrocarbon reduction alteration successively, the top sandstone of Yan'an formation is characterized by poor cementation degree and easy to be eroded by flowing water. The bleaching phenomenon in clastic paleo-weathering crust is an important indicator to identify unconformity structure and participate in hydrocarbon migration and accumulation.
【作者单位】：西安石油大学地球科学与工程学院;西北大学地质学系大陆动力学国家重点实验室;中国海洋石油(中国)有限公司天津分公司;
【基金】：中国地质调查局项目(编号12120114009201) 国家自然科学重点基金项目(编号41330315,91214301) 西北大学研究生自主创新项目(编号YZZ13013)联合资助成果
【分类号】：P534.52;P618.13

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