The definition of triangle zone and its petroleum prospecting significance.

Triangle zones normally develop in foreland fold-and-thrust belts and become favorable object of petroleum exploration. The geometry and nomenclature of triangle zones vary from place to place, among which Alberta-style triangle zone is of common significance. Progresses have been made on triangle zones in that a large number of work have been done at home and abroad in recent years. Based on physical and numerical modeling and integration of geological data, different kinematic and genetic models have been proposed, in which two kinematic models and a genetic model, prograding monocline model, are presented in this paper. Factors influencing the formation and development of triangle zones include décollement, variation of mechanical stratigraphy, syntectonic sedimentation, erosion and so on. Owing to their complexity in structure, triangle zones commonly have poor quality on seismic profiles. Consequently, seismic modeling and strata-in-growth method can be used to identify triangle zones. Seismic explorations demonstrate that triangle zones are widely distributed in zones around the basins in western China, and several examples are shown in this paper.