Torsion structures and their bearings on the hydrocarbon accumulation in southern Huanghua depression, Hebei

Abundant oblique slip faults characteristic of the torsion structures occur in the Tertiary cap rocks of the Huanghua depression. The torsion structures in the depression comprise two types:translational structures and rotation-torsion structures. The former appear in the areas bounded by the Cangdong fault, Xuxi fault, Nanpibei-Yanshan concealed fault and Zaopo-Guxian concealed fault, and display the structural patterns of the λ-type, en echelon and "S" shapes. The latter appear dominantly in the Wumaying region in the southern part of the Nanpibei-Yanshan concealed faults, and secondly in the Shenusi region on the downthrown side of the Cangdong fault. The tenso-shear fault systems may exercise an important control on the formation of traps and faulted zones, vertical migration of hydrocarbons, and different controls on hydrocarbon accumulation.