Abstract:

To determine the structural style and stratum distribution in the Miquan area in the piedmont of Bogda Mountain, the paper establishes a typical thrust decollement style in the study area based on the study of the fault development characteristics and the controls of detachment layer on structure development. Restricted by the Upper Triassic mudstone and the detachment coal layer in the Lower Jurassic Badaowan formation, the basement fault which underwent a low-angle slip and thrust from south to north along the detachment layer at the early stage and a updip at the late stage incised into the strata and exposed on the surface, and displayed a unique deckchair-like shape. The secondary faults are of small scale, whose ends are located in the detachment layer. The piedmont of Bogda Mountain is divided into 3 large structural belts such as nappe belt (basement nappe), thrust belt and decollement belt. Miquan area located in the thrust belt can be divided into 4 structural steps laterally and 3 structural layers vertically. Each structural layer is an active-roof duplex and the development degrees of the secondary faults are different from each other. The establishement of the thrust decollement style has overturned the preliminary understanding about the structures. It is considered that the strata under the nappe still belong to the lower reservoir-forming combination where many favorable traps could be discovered. The understanding has great significance for petroleum exploration in the lower combination in the piedmont of the southern margin, Junggar basin.

Key words: Junggar basin, Miquan area, thrust decollement, detachment layer, Upper Triassic, Lower Jurassic, nappe belt, thrust belt, decol-lement belt, lower reservoir-forming combination