Deformation characteristics and analog modeling of transtensional structures in the Dongying Sag, Bohai Bay Basin

Abstract

Hydrocarbon exploration in the Dongying Sag is constrained by the development of many Cenozoic transtensional structures with complex patterns and dynamic mechanisms. This study uses seismic interpretation and analog modeling to investigate these transtensional structures. Significant results include dividing these transtensional structures into boundary fault, oblique rifting, and deep strike-slip fault controlled structures, according to the relationships between main and secondary faults. They developed in the steep slope zone, the central sag zone, and the slope zone, respectively. In profile, the transtensional structures formed appear to be semi-flower-like, step-like, or negative-flower-like. In plan-view, they appear to be broom-like, soft-linked, or en-echelon structures. Further, these transtensional structures are controlled by the oblique normal slip of boundary faults, by the oblique extension of sub-sags, and by the later extension of deep strike-slip faults. The geometric deformation of these transtensional structures is controlled by the angles between the regional extension direction and the strike of boundary faults, deep faults, or sub-sags, where a larger angle corresponds to less developed transtensional structures. Further, the transtensional structures in the Dongying Sag were created by multiphase and multi-directional extensions in the Cenozoic— which is also controlled by pre-existing structures. The strike of newborn secondary faults was determined by the regional extension direction and pre-existing structures.