CHARACTERISTICS OF JIYANG DEPRESSION AND MECHANISM OF BASIN FORMATION

Jiyang depression consists of a number half-graben sags and some swells. The swells are distributed along NE direction. Single swell extends in EW. EW trending faults are the major structures in the Dongying sag. In the western part of the Jiyang depression, the sags are distributed in NE, and the NE faults are the major controlling structures. Extensional structures predominate in Jiyang depression, while few strike-slip structures and gravitational slip structures also occur in this depression. Jiyang depression has undergone the compression phase along NE direction in Indosinian orogeny, the rifting phase in middle Mesozoic, the uplifting phase in late Mesozoic, strong fault basin phase in Eogene and the integral depression phase in Neogene. The formation of Jiyang depression was due to the rifting of lithosphere caused by mantle uplift and to the pulling-apart effect of strike-slip faults, and the extrusion originating from the Pacific Oceanic plate controls the formation of the half-graben basin.