南海珠江口陆架区第四纪高精度层序地层构型、时空差异及控制因素

High-frequency sea level changes, together with active neo-tectonics, locally strong hydraulic regimes and unique climatic signals, make the Pearl River continental shelf of the South China Sea to be a “natural laboratory” for investigating the Quaternary sequence stratigraphy and its spatial-temporal variability on shelves. The first aim of this proposal is to identify and track the sequence boundaries and associated bounding surfaces of systems tracts, thus to construct high-resolution stratigraphic framework with a four-fold subdivision scheme. After that, the chronostratigraphic control will be achieved though the correlation with a few shallow wells. Two key unconformities, including the unconformity of the MPT completion and the unconformity of last glacial maximum, would then be recognized, to reveal the temporal variability of the sequence stratigraphic architectures that driven by distinct glacio-eustatic cycles. At the meantime, the lateral variability will then be studied by comparing stratigraphic architectures along depositional-strike. Finally, sequence stratigraphic numerical modeling will be applied to build an 3D forward model for the spatial-temporal evolution of Quaternary depositional sequences and to reveal the influencing mechanisms of various regional and local controlling factors.

高频的海平面变化、活跃的新构造运动、局部强水动力及独特的气候信号，使南海珠江口陆架区成为研究第四纪层序地层及其时空演变的“天然实验室”。项目基于最新采集的单道地震资料，首先对主要的层序界面及体系域界面进行识别和对比，建立“四分体系域”级别的高精度层序地层格架。进而结合陆架区浅钻资料，对层序地层格架进行年代学约束，重点厘定中更新世气候转型完成期和末次盛冰期两个时间节点所对应的重大不整合界面，揭示不同冰期—海平面旋回控制下的层序地层差异演化特征。同时，针对典型层序开展横向的对比分析，查明层序地层结构的侧向变化规律。最后，采用沉积层序数值模拟的研究方法，建立研究区第四纪层序时空演化的三维正演模型，进而阐明各类区域控制因素及局部控制因素对层序发育时空差异性的控制机理。

第四纪陆架层序的发育样式是对物源、海平面、构造和气候变化的综合响应，具有较大研究价值。基于高精度单道地震测网和陆架浅钻，本项目针对南海北部珠江口第四纪陆架层序结构和演化开展了精细刻画。研究厘定出了可用于区域对比的三种主要界面类型，包括侵蚀面、平整面和高频界面等，并阐明了其各自的层序地层学内涵。在此基础上，通过与已发表和新获取的浅钻定年资料标定，获取了较为可信的年代地层格架。进而，系统阐述了珠江口陆架第四纪层序结构的时空差异性及其主控因素。空间尺度上，正对河口和偏离河口区的层序结构对比揭示了层序发育的横向变化性，提出沉积物输入位置、东沙隆起抬升和局部水动力强度等局部因素可能是主要控制因素。时间尺度上，针对中更新世气候转型不整合面开展了系统厘定，提出该重大气候事件前后研究区层序地层特征发生明显差异，下切河道、陆架边缘三角洲等仅在气候转型完成后开始大规模发育。针对层序地层发育的数值模拟印证了气候旋回控制下的海平面升降幅度和结构对于最终的层序地层样式具有明显控制作用。研究得到的相关认识对于理解第四纪变化具有重要意义，所建立的层序模式对于珠江口盆地陆架区油气勘探具有一定指导价值。