The Cenozoic Tectono‐Thermal Evolution of Jiyang Depression, Bohai Bay Basin, East China

AbstractThe thermal history of the sedimentary basins is an important parameter for the study of tectonic evolution, hydrocarbon accumulation and resource assessment. The thermal gradient evolution histories of 70 wells during the Cenozoic time in the Jiyang Depression were modeled by using the vitrinite reflectance and apatite fission track data in this paper. Based on these modeling results, the characteristics of thermal evolution of the Dongying, Zhanhua, Huimin and Chezhen sags in the Jiyang depression were analyzed. The thermal gradients of the depression decreased during the Cenozoic time. However, it decreased quickly in the Eogene, but only changed a little during the Neogene time. The thermal gradient was 54.0~50.0°C/km during the deposition of the Kongdian Group, 50.0~40.0°C/km during the period of Shahejie group, 40.0~38.5°C/km of Dongying group and 38.5~35.5°C/km during the Neogene. It changed little after that time and decreased down to 35°C/km at the present‐day. The four sags had different thermal evolution history, especially after the Dongying tectonic movement at the end of Eogene. The thermal gradient of the Dongying sag is the highest, then the Zhanhua sag is next, the Huimin sag is relative lower and the Chezhen sag lowest. The Chezhen sag underwent the lowest thermal history during the whole period of Cenozoic time. The differential thermal gradients resulted in the different threshold depth of hydrocarbon generation in the four sags. The modeling results of thermal history fits well with the evolution stages of rift‐subsidence basin to down‐warped basin by the tectonic subsidence analyses of the Jiyang depression.