Abstract: Host formation in Santanghu basin is made up of Permian foreland basin superimposed with Mesozoic depression basin. It is considered that Santanghu basin was in a south-north compressional stress environment from Hercynian to Y anshanian stages, and the regional stress field was nearly south-north by analysis of the palaeostructural trackway patterns of Permian and Mesozoic. In Hercy nian gional stress field was nearly south-north by analysis of the palaeostructural trackway patterns of Permian and Mesozoic. In Hercy nian stage, the compressional stress field changed into rotational shear stress field in Malang sag, and thus led to the creation of brush structural sy stem, due to the nuclear column efect of Chahaquan swell. In Yanshanian stage, the nearly parallelogram boundary of Tiaohu sag made the nearly south-north regional stress field tur into a normal shear one, hence an en echelon structural system formed at the north slope of the sag. The southern margin of the basin has always been in a frontal belt of north-east positive pressure since Hercy nian stage ,so many huge decollement faults and s series of gliding nappe systems with single-row or superimposed styles developed. In the southern margin of Ma lang sag, several superimposed gliding nappe systems exist in the Permian strata beneath Baiyishan Carboniferous nappe, forming striangle structural belt. W ith abundant faults and fractures, the triangle belt could be a favorable area for fractured reservoirs.

Key words: Santanghu basin, structure, superimposed structure, structural belt, stress field