多幕裂陷盆地断裂生长演化及砂体分配响应机制—以南海珠江口盆地陆丰凹陷为例

Recently, the tectono-sedimentary evolution in multiphase rifts has attracted lots of interests worldwide. The relationship between normal faulting and sediment dispersal patterns in multiphase rift basins has become a hot scientific issue that needs to be further analyzed. The Pearl River Mouth Basin, one large offshore oil-bearing basin in the northern South China Sea, has undergone two phases of rifting during the Eocene, associated with various types of depositional systems. This basin could be a good example to understand the interaction between multi-phase faulting and depositional patterns. The Lufeng Sag of the Pearl River Mouth Basin is selected as the main research object in this project. We use the full-covered 3D seismic data, logging data and core data to establish the relationship between the normal fault arrays evolution and sandstones dispersal patterns in this two-phase rift. Firstly, sequence stratigraphic framework is established based on the seismic, logging and core data; the geometries and kinematics of the major and secondary faults are finely described based on the seismic profiles and structural maps, and fault growth and interactions during the two-phase rifting are illustrated. Secondly, the provenance and sedimentation evolution patterns are revealed based on an integrated analysis of zircon, heavy mineral and seismic sedimentology studies. Finally, the controls of the two-phase faulting on the depositional patterns including the entrance location of sediments, dispersal pathways and sandstone distribution are discussed. The established tectono-sedimentary model in the study could provide useful insights to the multi-phase rift evolution, and also has significant implications for large-scale sandstone prediction and petroleum exploration.

多幕裂陷盆地构造-沉积演化研究是当前地质学领域关注的重要科学问题，多期的断裂生长及演化特征与沉积物分散方式的研究又成为需要深入研究的热点科学问题。中国南海北部的珠江口盆地经历了始新世两幕裂陷旋回并发育多种类型的沉积体系，是开展多裂陷盆地分析的理想对象。本项目拟选取具有丰富三维地震数据、测井和岩心资料的珠江口盆地陆丰凹陷为研究区，探讨并建立两期断裂生长演化与沉积物分配的模式。在建立层序地层格架的基础，首先定量剖析边界断裂和次级生长断裂，确定断裂的几何学和运动学参数，阐述同生断裂的生长规律及组合方式；其次，利用锆石、重矿物分析及地震沉积学方法结合测井和岩心资料，全面厘清物源体系、沉积物分散及演化规律；最后，建立两期断裂体系生长演化与沉积物入口位置、分散路径和砂体展布特征的演化模式。研究成果不仅对揭示多幕裂陷盆地构造-沉积演化规律具有重要的理论意义，而且也为寻找大型砂体和油气资源提供了地质依据。

多幕裂陷盆地层序结构和沉积充填方式的协同机制是当今国际地学领域研究热点和难点，第二幕裂陷阶段断层复活机制和其层序-沉积响应规律尚不明晰。本项目主要选取珠江口盆地陆丰凹陷为研究对象，并横向类比研究珠三凹陷和西湖凹陷，探讨并揭示了多幕次裂陷构造演化过程对层序及沉积样式的控制作用。项目研究结果主要包括：1）提出和推广了多尺度测井变换的层序界面定量识别方法体系，明确了陆相裂陷盆地多级次层序驱动机制；2）揭示了陆丰凹陷两幕裂陷“跷跷板”构造迁移过程，建立了珠江口盆地多幕次应力场偏转下的构造动力学机制模型，认为断裂走向与应力场偏转综合决定了第二幕次断裂的优势活动性特征；3）针对不同构造背景以及国内外综合实例，综合建立了四套两期断裂演化的特色模式；3）系统分析了断陷湖盆边界断层活动特征，并构建了不同幕次阶段的构造地貌、层序厚度、层序结构配置关系；4）提出在裂陷盆地演化的早期，分割型洼陷主要以陡坡带和缓坡带水系供源为特征，而在断裂发生连锁之后轴向水系供源体系逐渐占据主导；5）阐明了第二幕裂陷阶段水系分散的特殊性，即以特定的边界断层迅速生长和复活为特征且其位移量快速达到最大，抑制了侧向水系供给但利于长轴水系搬运沉积物进入湖盆，是第二幕裂陷盆地广泛“富砂”的驱动机制。截至目前，已在《Marine and Petroleum Geology》、《Acta Oceanologica Sinica》、《地学前缘》、《沉积学报》等主流期刊发表论文12篇，其中SCI收录4篇，地学卓越T1梯队期刊6篇；获得专利授权以及省部级科技进步一等奖各1次，主持分会场报告1次，获邀担任国际SCI期刊《Australian Journal of Earth Science》副主编，以及国内期刊《中国矿业大学学报》、《China Geology》等青年编委。项目研究成果可直接服务于国家能源勘探与开发，并在东海、南海等盆地深层陆相油气勘探中得到了广实践。研究成果为陆相湖盆演化提供了新的理论模型，对多幕裂陷盆地构造-层序-沉积协同机制研究具有重要科学意义。