Study of characteristics of the Cenozoic geotemperature field in Jiyang Depression

Geothermal history of Jiyang Depression was reconstructed through synthesizing apatite fission track and vitrinite reflectance model offered in this paper.The study on the relation between four sags of Jiyang Depression and paleogeothermal results indicate the geotemperature gradient in Jiyang Depression re-duced gadually,the geotemperature gradient reduced rapidly in the Eogene period and then it was slowly.There is difference in thermal evolution in these four sags,especially after Dongying movement which oc-cured in late Eogene.The highest paleogeothermal field occurred in Dongying Sag,followed by Zhanhua Sag,Huimin Sag and Chezhen Sag.The evolution of source rocks is related tightly to paleogeothermal field.In high paleogeothermal field,source rocks entered oil threshold in shallower formation.