Cenozoic sequence stratigraphy and sedimentary evolution of forearc basin in Ryukyu Island Arc region

Abstract

琉球弧前盆地位于菲律宾海板块北部与欧亚板块汇聚部位，发育于琉球海沟北部增生楔与琉球岛弧之间，是典型“沟-弧-盆”体系的组成单元。现利用多道地震资料，首次建立琉球弧前盆地的层序地层格架，分析其新生代层序地层特征，阐明弧前盆地沉积充填演化过程，并探讨各盆地主要物源。通过地震剖面解释分析，表明:①始新世为岛弧变质基底沉积期，晚渐新世晚期-早中新世阶段发育残余伸展盆地基底沉积，属于浅海环境，主要受岩浆活动影响，发育火山碎屑岩相；②中中新世-第四纪时期是弧前盆地的主体沉积期，盆地从半深海沉积环境向深海环境过渡，发育典型深海沉积相，局部为火山碎屑岩相；中中新世时北部的南琉球群岛是弧前盆地主要物源区；晚中新世至第四纪时期，台湾岛东北部陆区成为对该弧前盆地贡献最大的物源区，而南琉球群岛的物源供给量降为次要地位。该研究结果是对琉球岛弧及周缘构造控盆作用研究的拓展，并对台湾岛陆地与东部海域“源-汇”系统研究有重要的指导意义。;The Ryukyu forearc basin is located at the convergence of the northern Philippine Sea plate and the Eurasian plate. It is developed between the accretionary wedge in the northern Ryukyu trench and the Ryukyu Island Arc. It is a component unit of a typical 'trench-arc-basin' system. Now, based on the multi-channel seismic data, the sequence stratigraphic framework established for the first time in the study area is used to analyze the Cenozoic sequence stratigraphy and sedimentary evolution characteristics, and discuss the main source of sediment. According to the characteristics of seismic reflection and the contact relationship of reflection layer group, it is revealed that the Cenozoic in the study area experienced the process of shallow marine facies, semi-deep marine facies and deep-sea facies. It is considered that island arc metamorphic basement sedimentation developed in Eocene, and the basement sedimentation period of residual extensional basin from Late Eocene to Early Miocene belongs to the basement sedimentation period of fore arc basin, which is a shallow sea environment and mainly develops pyroclastic lithofacies; The Middle Miocene to Quaternary is the main sedimentary period of the forearc basin. It transited from the bathyal to the deep-sea sedimentary environment. The local volcanic clastic facies developed many typical sedimentary systems, such as gravity flow, turbidite fan, underwater delta and turbidite channel. It is inferred that the South Ryukyu Islands in the northern part of the Middle Miocene was the main provenance in the forearc basin period. Since the Late Miocene, the land area in the northeast of Taiwan Island has become the largest provenance, and the South Ryukyu Islands is in the second place. The results are an extension of the study on the basin control of the Ryukyu Island Arc and its surrounding structures, and have important guiding significance for the study of the 'source-sink' system of the land and eastern sea area of Taiwan Island.