NEGATIVE INVERSION STRUCTURE IN THE JIYANG DEPRESSION AND ITS PETROLEUM GEOLOGICAL SIGNIFICANCE

The Jiyang Depression is an important Mesozoic-Cenozoic petroliferous basin in East China. In the past, it is always considered as a pure tensional fault basin. However, the latest descovery of negative inversion structure in the basin and its study show that the basin experienced alternate negative inversion and positive inversion stages in the early development period of the Mesozoic, and presents the characteristics of negative inversion structure on the whole. In this paper, the types and characteristics of negative inversion structure are studied, the "thin-based" and "bald-based" two types of negative inversion folds as well as "paranormal fault type" and "upper-normal and lower-reversed mixed type" two categories and four subcategories of negative inversion faults are identified, and the formation and evolution of the basin and the negative inversion structure are discussed. It is pointed out that the negative inversion structure has important significance to basin genesis, tectonic belt evolution, complex hydrocarbon accumulation-belt patterns, pool formation and prediction, etc.