中国西部陆内前陆盆地沉积特征与层序格架

Sedimentary Characteristics and Sequence Framework of Intracontinental Foreland Basin in the Western China

中国西部陆内前陆盆地发育于造山带与克拉通之间,是板块碰撞后陆内远程效应引起冲断作用所形成的一种盆地。它与国外典型前陆盆地有一定的差异,不存在被动陆缘所形成的海相生油岩系及海相磨拉石建造。陆内前陆盆地同样富集油气,近年来广泛地受到石油地质界的关注。文章从多个方面研究分析了陆内前陆盆地与典型前陆盆地的差异性,认为其主要沉积特点是冲断作用期粗粒沉积物的叠加可形成连续的裙边状沉积体;冲断作用松懈期发育的煤系地层及泥质岩可形成良好的烃源岩;沉降中心的不断迁移与沉降中心和沉积中心的偏移现象普遍。根据沉积物叠加样式将陆内前陆盆地分为前展型、上叠型和后退型三类,并建立了相应的沉积层序格架。最后据不同类型的盆地分析了其油气生成、储集和保存条件,这将有利于根据不同的样式针对性地进行油气勘探,从而提高勘探效率。

Located in the area between orogenic belt and craton, intracontinental foreland basin in Western China was formed by the intracontinental fold-thrust movement resulted from the long-distance effect of plate collision. Without marine source rocks and marine molasses that are always developed along the passive continental margin, the intracontinental foreland basin is different fro,n the typical foreland basin in foreign eountries to some extent. With abundant hydrocarbon resources, the intracontinental foreland basin has attracted increasing attention of petroleum geologists in recent years. Main differences betweeu intracontinental foreland basin and typical foreland basin have been analyzed and main sedimentary characteristics of the intracontinental foreland basin have been proposed. During the fold-faulting episode, the superposition of coarse-grained sediments could form apron-shaped sedimentary body. While during the inactive period of the fold-thrust movement, the well-developed coal bed and mudstone could form source rocks of high quality. However, during the whole process, the migration of depression center and the excursion between depression center and deposition center are eommnn. According to the superposition style of deposits, the intracontinental foreland basin has been subdivided into step-forward, superposition and step-backward types and sedimentary sequence model for each type has been established. Finally, the hydrocarbon generation, accumulation and preservation condition of each type of basin have been discussed, which will be helpful to the hydrocarbon exploration according to their respective sequence model and to the improvement of exploration efficiency.