Abstract:

The middle section in the west margin of Ordos basin, located between Ordos Block and Qinling-Qi-lianshan fold belt, is an important part of the west margin tectonic belt. Many studies have been carried out about the surface structural features in recent years, but the underground structural features and structural modes are not clear till now due to the complex structural deformation and poor seismic imaging quality making identification of underground structures difficult. Integrated surface geology and a mass of high-quality seismic data, given the decollement from flyschoid turbidites of Lower Paleozoic to coalmeasures of Upper Paleozoic as a detachment, two structural systems can be divided vertically which are the thrust nappe tectonic system in the upper part and the autochthonous system in the lower part. The former is constituted of six thrust sheets with intensive deformation of folds and faults, which are Luoshan thrust sheet, Weizhou thrust sheet, Shigouyi thrust sheet, Yandunshan thrust sheet, Jijiajing thrust sheet and Majiatan thrust sheet, has obvious lateral zonation characteristics and is divided horizontally into three parts from west to east in this area, such as overthrust structural body, frontal transitional zone and front zone. The autochthonous system is a west-dipping monocline with weak structural deformation, and complete anticlinal traps are developed in local area. A greater exploration prospect for oil and gas can be assumed in the frontal transitional zone, the front zone and the autochthonous system due to numerous exploration targets and good geological conditions of hydrocarbon accumulation. The Cambrian to Jurassic exploratory objectives are exposed, together with the intense deformation of faults, the generation and preservation of hydrocarbon become poor, herein making petroleum exploration potential poor in the overthrust structural body.

Key words: structural mode, decollement, thrust nappe tectonic system, autochthonous system, explorationprospect