Differences of polygonal faults related to upper Miocene channels: a case study from the Beijiao sag of Qiongdongnan basin, South China Sea

Distribution Patterns and Genesis of Geological Fractures/Microfaults in the Qiongdongnan Basin, North of the South China Sea

“…Polygonal faults are present in neither ultra-shallow layers nor in the deep basin, but rather in certain layers beneath the seismic anomaly (Figure 4). Although many theories have been put forth in order to explain how polygonal faults form, including density inversion [53], syneresis [54][55][56], a low coefficient of friction [57] (Goulty and Swarbrick, 2005), gravity sliding [58], or a genetically shear failure [59], their formation in this area is largely related to the syneresis that results from gravitational spreading and the overpressure of hydrofracture [60]. In geneses, firstly, the main fault in deeper formations partially controls these polygonal faults, and the continuous activity of the main fault causes the differential subsidence of its down wall (Figure 4), which leads to the inhomogeneous compaction of the sedimentary layers.…”

“…In geneses, firstly, the main fault in deeper formations partially controls these polygonal faults, and the continuous activity of the main fault causes the differential subsidence of its down wall (Figure 4), which leads to the inhomogeneous compaction of the sedimentary layers. Li et al [60] also found that, because sandstone is less fluid-confined than mudstone, their capacity for dehydration differs, which leads to a difference in the extent of polygon development. For example, the polygonal fault scale near the sandstone in this region is smaller than that in the mudstone, that is, the large-grained sandstone inhibits the formation of a polygonal fault because it has a superior effect regarding pressure relief.…”