Tectonic Characteristics of the Juyanhai Depression in the Yingen-Ejinaqi Basin, Inner Mongolia, China, Based on Gravity, Electrical, and Seismic Data

To determine the tectonic characteristics of the Juyanhai Depression in the west of the Yingen-Ejinaqi Basin, gravity data in the study area were processed and analyzed on the basis of the collection of existing geophysical data. Then, fault systems in the Juyanhai Depression were comprehensively presumed and explained mainly using processed gravity data in conjunction with the electrical and seismic data. Existing tectonic units in the depression were divided and studied afterward. There are mainly three groups of faults in the Juyanhai Depression, namely, the NE (or NNE)-, NW (or NWW)-, and nearly EW-trending ones. Faults not only control the thickness difference of sedimentary strata on both sides but also play an important role in controlling the formation of local structures and hydrocarbon accumulation. The Juyanhai Depression can be categorized into 13 primary structures, including six arches and seven sags. The sags and arches are independent, separated, and distributed in rows along the NE (or NNE) trend on the whole. According to structural patterns, sags can be classified into single-fault and double-fault ones. The characteristics of single-fault sags are that their formation is controlled by the main controlling normal faults of boundaries, manifested as half-graben fault depressions. The characteristics of double-fault sags are that their formation is controlled by the normal faults on both sides, while the fault distance of the sag-controlling faults differs on both sides. The research region has good prospects for a variety of resources, including oil and gas, shale oil and gas, coal, and uranium, and the distribution of these resources is closely related to the range of tectonic units. Therein, oil-gas exploration should mainly focus on sags. In the shallow part of the sags, fault-anticlines, fault blocks, fault-screened traps, and lithologic oil-gas reservoirs in the slopes should be the main targets of exploration. In the deep part of the sags, the bedrock buried hill reservoirs and the igneous rock lateral-screened oil-gas reservoirs formed by igneous intrusions are favorable exploration targets.