【摘要】 渤海位于渤海湾新生代裂陷盆地中段的东部。最近用大量三维地震勘探资料对渤海第四系及其构造所做的精细解释和分析,发现地层内普遍存在4个不整合(角度和平行不整合)面,表明曾发生过4期构造活动。但因渤海缺少完整的第四系岩芯剖面,无法对其进行系统分层和断代,更无从确定构造活动的时间。为解决这一难题,文章基于渤海湾盆地阶段性沉降和其周围山地间歇性抬升的相关性,以及它们具有统一的形成机制和同一动力学过程的认识,通过研究盆地周围山地第四纪构造运动塑造的多级河流阶地,并结合火山活动研究资料,推测渤海第四系内4个不整合面形成的时间是900~400kaB·P·,100~80kaB·P·,50~40kaB·P·和10~8kaB·P·,即早更新世晚期-中更新世早期、晚更新世早期和中期、全新世早期。更多还原

【Abstract】 The Bohai Sea is located in the eastern part of a Cenozoic rift basin, the Bohai Bay Basin in North China. Recently fine interpretation and analysis have been made to the Quaternary System and its structure in the Bohai Sea by using three-dimensional seismic exploration data. It is found out that there broadly exist four unconformable interfaces (angle and plane unconformity) in the strata, indicating four tectonic activities. Due to the lack of complete core profiles of the Quaternary System in the Bohai Sea, it is difficult to make precise systematic division and dating analysis of the strata. The exact time of every tectonic activity can neither be determined. To solve this problem, we attempt to use the geomorphic features of the surrounding mountainous areas to estimate the tectonic episodes of Quaternary in the Bohai Sea. The basic rationale is that the subsidence of the Bohai Bay Basin is associated with the uplift of its surrounding mountainous areas, which produced multi-grade river terraces in Quaternary time. Previous studies indicate that the North China region experienced extensive erosion and leveling off in Late Cretaceous time (95～65MaB.P.), leading to large-scaled peneplanation and finally resulting in a wide peneplain of the Beitai period. Afterwards, Cenozoic rifting made this peneplain broken down, subsiding to become basins, inlcuding the Bohai Bay Basin. Meanwhile, the surrounding areas uplifted to form mountains. When this process tended to be stable in Pliocene, the valleys and piedmonts in the mountainous areas reached the peneplain state, forming the leveling plane of the Tangxian period with wide valleys intervening with residual hills. Correspondingly, the basin-range system in the Bohai Bay Basin of Eocene was covered with the Oligocene Series which constituted the base for the Quaternary landforms. With intermittent uplift of mountainous areas in Cenozoic, river terraces of four grades developed widely below the leveling off plan of the Tangxian period. By using a great number of dating data of sediment in the terraces, statistic analysis is performed in this study to determine the stages of intermittent uplift of the mountainous areas. Comparing these stages with the sedimentary processes of the Bohai Bay Basin in Quaternary, in conjunction with the dating data of Quaternary volcanic rocks on the edge of Bohai Sea, we estimate that the Quaternary System in the Bohai Sea has four times of unconformity formation, 900～400kaB.P., 100～80kaB.P., 50～40kaB.P., and 10～8kaB.P., i.e., late Early Pleistocene -early Middle Pleistocene, early Late Pleistocene, middle Late Pleistocene, and Early Holocene.更多还原