地质学报2017，Vol.91Issue(6)：1345-1359,15.
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
White Bleached Sandstone Genesis and Paleo-Weathered Crust Forming Environment of the Jurassic Yanan Formation in the Northeastern Ordos Basin
摘要
Abstract
Bleached white sandstone represent the evidence of hydrocarbon migration in the northeastern Ordos Basin.Previous studies only focus on the chemical bleaching from the perspective of hydrocarbon-rock interaction,but ignoring its forming environment.Bleached sandstones in study area only distribute in the weathered rock under the Jurassic unconformity,indicating unconformity played important role in the formation of bleached white sandstone.Combining field,petrographic,and geochemical analyses,the characteristics of unconformity structure were deeply investigated.The results show that the weathered clay zone is not developed in the Jurassic unconformity.The unconformity structure can be classified into two types:weathered rock zone developed (type Ⅰ) and non-weathered rock zone developed (type Ⅱ).Sandstone in the upper part of weathered rock is composed of quartz and kaolinite,marked by secondary pores by dissolution,kaolinization of biotite,and loss of alkali and alkaline earth elements(K,Na,Ca,and Mg).K-feldspar content is higher in sandstone of the lower part of weathered crust,and biotite was partially weathered to hydro-biotite,K and Mg were retained in K-feldspar and hydro-biotite.Pore fluid exchange was restricted in the fine-grained sediments,with low porosity and permeability,causing weaker weathering process and hydrocarbon-induced alteration.Kaolinite in white sandstone was the product of weathering process,rather than product of hydrocarbon-rock interaction.Weathering enhanced the porosity and permeability of sandstone and oxidation during weathering led to the formation of iron oxides grain coatings,which changed the colour of sandstone from gray/green to red.Hydrocarbon reduction caused migration of Fe and bleaching of red weathered sandstone,which further decreased the degree of cementation after weathering.Hydrocarbon-induced sandstone bleaching is a key record of hydrocarbon migration and accumulation in paleo weathered clastic rock.关键词
漂白砂岩/不整合结构/碎屑岩风化壳/流—岩相互作用/鄂尔多斯盆地Key words
sandstone bleaching/unconformity structure/weathered clastic crust/fluid-rock interaction/Ordos Basin引用本文复制引用
张龙,刘池洋,雷开宇,孙莉,寸小妮,杜芳鹏,邓辉..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[J].地质学报,2017,91(6):1345-1359,15.基金项目
本文为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)和西北大学研究生自主创新项目(编号YZZ13013)联合资助成果. （编号12120114009201）
