Recovery and comparative research of thermal history on Jiuquan basin group

Jiuquan basin group is formed by the stacking of two-stage basins with diff erent property and different generation. It was rift basin in Late Jurassic -Early Creaceous and squeezed sag basin since Cenozoic. The present geother mal gradient between 2.5 degrees C/100m and 3.00 degrees C/100m and heat fl ow between 50mW/m(2) and 57mW/m(2) is low in Jiuquan basin group. Jiuquan b asin group is rift basin and its palaeothermal gradient is higher in late M esozoic, which reached 3.75-4.50 degrees C/100m. The thermal gradient has d ecreased since Cenozoic. Huahai basin and Shibei depression of Jiuxi basin have subsided at a small increase since Cenozoic, the palaeotemperature of lower Cretaceous source rock is higher than present, the maturity of lower Cretaceous sources rock is controlled by palaeotemperature. There is only o ne stage of main oil generation, Early Cretaceous. Qingxi depression of Jiu xi basin and Yinger depression of Jiudong basin have subsided at a big incr ease since Cenozoic, the maturity of lower Cretaceous source rock is mainly controlled by present temperature. There are two stages of main oil genera tion, late of Early Cretaceous and Late Tertiary, main stage of oil generat ion is Late Tertiary. The difference of tectonic thermal history in differe nt basin and different units of a basin result in difference of stage of ma in oil generation and difference of oil-gas exploration prospect.