Yanshan‐Himalayan Denudation in Western Hubei Eastern Chongqing Area

Abstract

AbstractWestern Hubei Eastern Chongqing area is a major exploration block of marine‐facies petroleum as well as a currently popular area of shale gas exploration. It has suffered long term uplift and erosion since the Late Yanshan‐Himalayan period. Erosion thickness is an indispensable basic parameter for study of thermal evolution of source rocks, reservoir formation and evolution, and basin modeling to calculate the amount of resources. Considering the inherent limitations and application conditions of the existing methods of erosion thickness reconstruction, firstly we used the paleogeothermal gradient inversion method to reconstruct the erosion thickness of boreholes after analyzing the vitrinite reflectance (Ro) profiles. Then, we studied the relationship between the erosion thickness of boreholes and the upmost sequences of the boreholes drilled. After that, a contour map was compiled based on the geological map. The results show that the vitrinite reflectance (Ro) profiles of boreholes in the western Hubei Eastern Chongqing area do not show obvious “dislocations” or “jumps”, recorded maximum palaeotemperatures of sequences in the maximum burial depth. There exists a clear correlation between the erosion thickness and the upmost sequence of the wells: the greater age of the upmost sequence, the greater erosion thickness of the well, and vice versa. Generally, the late Yanshan‐Himalayan erosion amount gradually decreases from east to west in the Western Hubei Eastern Chongqing area. From the Lichuan area to Shizhu and to the west of the Fangdoushan, the erosion thickness decreases from 2000∼4000 m to 1500∼2500 m and to 1000∼1500 m.