Characterization and Distribution of Cenozoic Polygonal Fault: Case Studies in West Africa and Vietnam Continental Margins
The Cenozoic sequence of offshore Cameroon and Vietnam has been analysed based on newly 1500 km2 3D seismic data (Kribi-Campo basin) and 75 km 2D seismic data (Hoang Sa basin). Polygonal faults are widely developed in both passive margins and have relatively similar characteristics. These highly faulted intervals are up to c. 1000 m, characterized by normal faults with a throw of 10-20 ms TWT and 100 m - 1000 m spacing, displaying a polygonal pattern in the map view. Polygonal faults in the Kribi-Campo basin developed almost in the entire Cenozoic sequence mainly in two sets, one in deep section and one in shallow section whereas the Hoang Sa basin developed the polygonal fault only in the shallow section up to the seafloor corresponding to the Pliocene- Pleistocene sequence. In the Kribi-Campo basin, polygonal faults are developed extensively in the high gradient slope (3.4o) which is relatively rare in the low gradient slope (0.7o). Hoang Sa basin shows the widespread polygonal fault except for the area of canyon occurrence. The occurrence of thick and widespread polygonal fault formations associated with the low amplitude reflections suggests the interpretation of fine-grained sediments, thus possibly great seal potential for the study areas.