【摘要】 基于高分辨3D地震资料研究得出,南海北部大陆边缘深水区的珠江口盆地白云凹陷、琼东南盆地华光凹陷、长昌凹陷和北礁凸起中新统普遍发育了延伸长度短、间距小、断距小、倾角大、受层序边界控制、平面呈多边形特征的小型伸展正断层,即多边形断层。借助区域相对海平面变化曲线、盆地构造和沉积演化、ODP钻井和深水油气井资料,探讨了南海北部多边形断层的形成机理。珠江口盆地白云凹陷和琼东南盆地华光凹陷多边形断层发育在海泛面对应的密集段上下,其形成受早期成岩过程中的压实脱水、黏土矿物相变脱水和生烃增压作用影响,可用超压泥岩水压破裂模型解释。琼东南盆地长昌凹陷和北礁凸起受复杂构造和沉积环境影响,多边形断层具有一定的定向性,地层岩性也较为复杂,除了受早期成岩过程中的压实脱水、水压破裂作用影响外,还受构造应力和重力扩展作用的叠加改造。更多还原

【Abstract】 Based on high-resolution 3D seismic data,the present study demonstrated that there exist small-scale extensional normal faults,i.e.polygonal faults,in the epicontinental deepwater area of the northern South China Sea,such as Baiyun sag of Pearl River Mouth Basin,Huaguang sag,Changchang sag and Beijiao high of Qiongdongnan Basin.These polygonal faults are sequence-bounded normal faults characteristic of short extension length,small spacing,small fault throw,high dip angle and poor directionality.Combined with data of regional relative eustasy curves,tectonic and sedimentary evolution,sequence stratigraphy,clay components of the ODP1148 site and log curves of a deepwater well,we discussed the formation mechanism of polygonal faults in the northern South China Sea.The occurrence of polygonal faults in the northern South China Sea has an obvious tendency of sequences becoming younger from east to west and from north to south.Polygonal faults in Baiyun sag of Pearl River Mouth Basin and Huaguang sag of Qiongdongnan Basin developed in the formations above or beneath closely-packed sequences corresponding to marine flooding surface.The formation of these polygonal faults was influenced jointly by compaction dewatering in early diagenesis and the dewatering of clay-mineral phase change together with the pressurization of hydrocarbon generation,which can be deciphered by a hydrofracturing model of overpressure mudstones.However,influenced by complex structural and sedimentary environments,polygonal faults in changchang sag and Beijiao high of Qiongdongnan Basin show certain directionality.The formation process was also relatively complex because it was affected not only by compaction dewatering and hydrofracture of early diagenesis but also by the reworking superimposed by structural stress and gravitation spreading.更多还原