广西百色利周地区板纳组中段砂质碎屑流沉积

Sandy debris flow of middle Banna Formation in Lizhou area of Baise, Guangxi province

广西百色地区中三叠世沉积了一套巨厚的浊积岩,其中也发育部分不协调的块状砂岩,尚未引起人们的关注,因此对其成因认识相对较为模糊。在观察多条野外地质剖面的基础上,结合前人的研究成果,重点对利周地区出露良好的地层进行了详细的剖面描述和采样分析,并依据岩性特征将其出露的板纳组中段分为滑塌角砾岩(岩相1)、薄—中层粉砂岩与薄—中层泥岩互层(岩相2)、中—厚层细砂岩夹薄层泥岩(岩相3)以及块状细砂岩夹极薄层泥岩(岩相4)4种岩相类型,推测利周地区中三叠世处于大陆斜坡环境,为近端水道沉积。根据岩石结构、沉积构造和沉积层序特征,认为岩相4应为砂质碎屑流沉积,它主要呈透镜体状充填于水道中,随着水道的迁移而叠置。最终建立了研究区中三叠统板纳组砂质碎屑流沉积模式,揭示出利周地区中三叠世时期经历了水道的侵蚀—迁移—废弃的过程。

A set of thick turbidite was found in the Middle Triassic in Baise area of Guangxi Province, where incoordinate massive sandstone which has not been aroused concern is also partially developed. Therefore the origin of the massive sandstone is still unclear. Based on the observation of several field geological sections and integrated with the precious research, we put emphasis on the detailed description and sample analysis of the strata which outcrops well in Lizhou area. According to the lithology characteristics, the middle part of Banna Formation in Lizhou area includes four lithofaeies： sliping collapse conglomerate （lithofacies 1 ）, thin to medium sihstone interbedded and thin to medium mudstone interbed （lithofacies 2）, medium to thick fine sandstone intercalated with thin bedded mudstone （lithofaeies 3 ） and massive fine sandstone intercalated with thin bedded mudstone （lithofacies 4）. These lithofacies may represent that the middle part of Banna Formation formed in the continental slope environment and it is proximal channel deposition. According to the rock textures, sedimentary structures and sedimentary sequence features, the lithofacies 4 is supposed to be sandy debris flow deposition which occurred as lenses in the channel, superimposing with the migration of the channel. Then, through the research above, a sandy debris flow depositional model of the middle part of Banna Formation in the study area has been built up, which reflects the evolution of the channel including erosion, migration and abandonment.