摘要:
通过对库车坳陷白垩系辫状三角洲的研究,总结辫状三角洲的沉积特征是:1.由于辫状河流直入湖泊,沉积物比较粗,中砂岩和细砂岩占有相当的比例,可达 6 0 %～ 80 %,最高达 95 %。 2.成分和结构成熟度低—中等,一般为长石砂岩、岩屑长石砂岩和岩屑砂岩,石英含量 30 %～ 5 0 %,岩屑含量可高达 5 0 %以上,一般为 30 %左右,岩屑成分复杂。3.沉积构造以块状层理、大型槽状交错层理和斜层理为主,见平行层理、波状层理和极少量的水平层理。4.辫状河道的主要沉积期是洪水期,因而河道具快速迁移性,沉积作用具有阶段性,砂体之间多次重复叠加,在滨岸地区辫状砂体性质相似而垂向侧向连接,成为分布面积很大的砂体,砂层之间只有薄层的泥质夹层。对研究区露头和岩心的普通薄片、铸体薄片、阴极发光及扫描电镜等资料的分析研究,认为该区成岩作用包括压实、胶结、溶蚀、交代、压溶和重结晶等作用,并且以前三类为主。根据对自生矿物、粘土矿物、I/S间层中的S %、包裹体测温、成岩作用类型及特点等分析,判断研究区白垩系成岩阶段已达晚成岩A期。白垩系砂岩储层特殊的沉积—成岩水介质条件、构造—埋藏演化史、异常高压背景等决定了其特有的成岩序列演化的特点。白垩系巴什基奇克组上部和底部、巴西盖组砂
Abstract:
The depositionai features of Cretaceous braided deita in Kuga depression can be conciuded as that（1）the sediments are very coarse, and the median-grained sandstone and fine-grained sandstone are the main rock types with a proportion from 60% to 80% of the totai sandstones. The maximum can be up to 95%;（2）most of these sandstones are composed of feidspathic, iithic feidspathic and iithic sandstone with 30% ~ 50% of guartz and rich in iithociast;（3）sedimentary structures are mainiy massive bedding, iarge trough cross bedding and obiigue bedding with few paraiiei bedding, wave bedding and horizotai bedding;（4）main sedimentary period of the braided channei is fiood stage, so the sedimentation is characterized by rapid migration of channeis with different stages to form thick and continuous sandstone iayers by iots of super imposed sandbodies, which are separated by some thin intercaiated peiitic beds. Based on the data obtained from thin sections, cathodoiuminescence and SEM of outcrop and core sampies, the diagenes can be determined as compaction, cementation, dissoiution, repiacement, pressure dissoiution and recrystaiiization.According to authigenic minerai, ciay minerai, 5% in mix-iayered I /S, inciusion temperature and diagenetic types, the diagenetic stage of the Cretaceous in the study area have reached a period of the iate diagenetic stage. Features of ciay minerais show speciai types and assembiages formed under aikiine diagenetic environment. There are abundant pore types in Cretaceous sandstones, which inciude intergranuiar pore, intragranuiar pore, grain-dissoived pore, matrix-dissoived pore, intercrystai pore, primary intergranuiar pore and structurai fractures.
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