Keywords: 
• C27trisnorhopane

Abstract: he Paleogene system in Dongying sag was the representative faulted lakebasin and also the typical cosedimentary system of evaporate and mud rocks in the Eastern of China. To investigate the evolution rule and its controlling factors on the maturation parameters relative to C27 trisnorhopane, the deep formation in the Paleogene System of four deep wells(Well Feng8, Fengshen1, Shi121 and Shi126 ) in the sag were intensively cored, tested and dissected, and the maturation parameters relative to C27 trisnorhopane in the main source rocks(the Member 3, Member 4 in Shahejie Formation and Member 2 in Kongdian Formation in the Paleogene System, the depth across from 2 700 m to 4 200 m) were investigated. The results demonstrate that in the depth across from 2.7 km to 3.572 km, the content of Ts and Ts+Tm(relative to the whole content of ions in the test of mass spectrogram 191) and the value of Ts/Tm, Ts/(Ts+Tm) increase with the buried depth added as a whole except the content of Tm, however in the depth across from 3.572 km to 4.2 km, the distribution of all the above parameters show the reversion. The research turns out besides the close relation between the maturation parameters relative to C27 trisnorhopane and the generation velocity of the isomers, thermal stability and isomerization of the isomers, the cracking of some polymeric compounds contribute to the increase of the relative amount of the Ts; thermodynamic activity control the distribution of these parameters primarily, while the relative low value of Ts/Tm, Ts/(Ts+Tm) in the salted deposition system show the influence of the sedimentary environment on the parameters; the well corresponding of the reversion of the maturation parameters to the high content of the carbonate minerals indicate the restrain and tardy effect of carbonate minerals on the thermal evolution of the organic matter. 