Abstract:

The Nanxiang (Nanyang-Xiangfan) Basin is a fault-subsided petroliferous basin of the Meso-Cenozoic. It covers an area of about 17000 km² with morethan 9000 m thick Meso-Cenozoic sediments. The Hetaoyuan Formation of the Lower Tertiary which reaches 3000m in thickness is the main source and reservoir beds. Up to now, seven oil fields have been found in this basin. The basin can be divided into three depressions. i.e. the Miyang, Nanyangand Xiangyang-Zaoyang Depressions, and four uplifts such as Xinye, Tanghe,Shigang and Sheqi Uplifts. The Miyang Depression abounds in oil and gas,the Nanyang Depression is secondary, and yet no oil show has been found inthe Xiangyang-Zaoyang Depression. The traps in the basin are mainly various noses. Eighty four percent of the proved reserves is in the nose traps. The basement of the basin is the Qinling folded belt and the Yangzi Platform.A series of NW compressed and compresso-shear faults developed on the PreMesozoic basement. From late Yenshan to early Himalayan movements, the NW faults reactivated and underwent sinistral displacement due to the closure of Tethys and the collision of the Indian Plate with the Chinese continent. At the same time, Tanlu fault zone moved in dextral displacement thus resulting the dextral motion of the NE faults. The motion strength of both NW and NE faults gradually increased. and fan-shaped fault blocks between them were made to move divergently, leading to the formation of the fan-shaped fault depressions. The tension made the crust thinner and the upper mantle uplifted.This in turn accelarated the subsidence of the crust. During the Late Tertiary,the mantle temperature dropped down gradually, elastic rebound and isostary changed the seperated. subsided basin into an unified depression.