洋陆边界的地层形变特征是研究洋盆张裂模式的重要窗口。最新的973地震测线显示，南沙北部郑和群礁海域洋陆边界处向陆一侧的地层被角度不整合分为两大套地层，上构层基本水平，角度不整合遭受强烈的剥蚀，而下构造层为异常厚的密集反射层，其下构造层反射特征和构造特征与南海其它地区洋陆边界的新生代沉积结构明显不同。该处下构造层形成时代的确定有利于加强对南沙张裂边界处地层属性和南海张裂模式的认识。本申请拟通过处理该处原有的和最新的小间距海底地震仪数据，获取沉积层高精度速度结构及其速度变化特征，通过该处不整合之下地层与南海确认的中生界和裂谷期地层特征的对比，井位投影、地震剖面地层特征的对比追踪，获取该处地层构造形变特征，最后确定该处下构造层的形成时代，探讨厚层沉积层的演化过程和新生代裂谷期该处地层的张裂模式。

The structure of the continent ocean transition (COT) at the northern Nansha Waters is an important window to study the evolution of the South China Sea (SCS). Thick strata with dipping and closely space reflection and high angle faults below angle disconformity are found aound Zheng`he Reefs located in the northern Nansha Waters. These phenomenon are very uncommon at COT of the SCS. However, it is being debated about whether the thick strata are pre-rift marine sediment during Mesozoic or syn-rift sediment during Cenozoic. The correct identification of the stratigraphic age is helpful to understand the property of OCT, the evolution model of the SCS and the Mesozoic distribution in Nansha Waters. Formation interval velocity and strata correlation are important methods of identification of Mesozoic and Cenozoic in the margin of SCS. In this program, new high resolution velocity structure will be acquired by reprocessing and processing the original and the latest OBS data around Zheng`he Reefs. Then velocity structure characteristics will be obtained by velocity comparison between Zheng`he Reefs and northern margin of SCS, where velocity of the Cenozoic and Mesozoic is known. The structural characteristics will be obtained by comparing with near well seismic line, strata correlation among strata below angle disconformity around Zheng`he Reefs and proven syn-rift and pre-rift strata of SCS. Baseed on the characteristic of velocity and structure, the age of thick strata below angle disconformity will be determined. At last we will make a preliminary study of the formation mechanism of thick strata.