Relationship between salt diapirism and faulting in the central structural belt of the Dongying sag, Bohai Gulf basin, China

摘要

Many growth faults developed in the Dongying sag of the Jiyang depression of the Bohai Gulf basin, China. These normal growth faults consist of flower-like grabens in the hanging walls of the major faults, accompanied by reverse dragging. The central structural belt is an important structural unit in the Dongying sag, and is divided into a series of small blocks by these faults. These internal blocks can be classified into five structural classes, including parallel blocks, arc-shape blocks, plume-like blocks, ring-radial blocks,and splay blocks. It is shown that these complicated block classes and the "negative flower-like" fault associations in the central structural belt resulted from regional NNW-SSE extension accompanying local salt diapirism and related reverse dragging, rather than strike-slip faulting. On the basis of the diapirism strength, diapers in the central structural belt can be divided into lower salt ridges and pillows, and blind piercing structures. Diapirs are mainly composed of some salts with a little soft mudstone and gypsum. These structures began forming during deposition of the Sha 3 member and terminated during deposition of the Guangtao formation.