Geochemical Characterization of the Eocene Coal-Bearing Source Rocks, Xihu Sag, East China Sea Shelf Basin, China: Implications for Origin and Depositional Environment of Organic Matter and Hydrocarbon Potential

Eocene coal-bearing source rocks of the Pinghu Formation from W-3 well in western margin Xihu Sag, East China Sea Shelf Basin were analyzed using Rock-Eval pyrolysis and gas chromatography–mass spectrometry to investigate samples’ organic matter, depositional environment, thermal maturity, hydrocarbon generative potential. The distribution patterns n-alkanes, isoprenoids steranes, high Pr/Ph ratios, abundant diterpanes, presence non-hopanoid triterpanes indicate predominant input higher land plants. contribution aquatic matter was occasionally slightly elevated probably due a raised water table. High hopane/sterane ratios occurrence bicyclic sesquiterpanes A-ring degraded suggest microbial activity organisms. Overwhelming predominance gymnosperm-derived diterpanes over angiosperm-derived domination gymnosperms angiosperms local palaeovegetation during period deposition. plot Pr/n-C17 versus Ph/n-C18, almost complete absence gammacerane, pattern hopanes that samples deposited relatively oxic environment. Generally, fluctuation redox potential is coupled with input, i.e., less conditions associated more suggesting an Comprehensive maturity evaluation based on Ro, Tmax, biomarker parameters shows constitute natural maturation profile ranging marginally mature near peak oil window. Hydrogen index atomic H/C O/C kerogens mainly contain type II/III could generate mixed gas.