An nalkane Coexisting Even and Odd Carbon Number Predominace of Paleogene in Jinhu Sag

Key words: 
• normal alkanes

Abstract: The data of source rock and oil samples reveal three distribution patterns of nalkanes in the second group of the Funing Formation in Jinhu Sag of Subei basin, eastern China. The three patterns are, respectively, the oddtoeven predominance，the eventoodd predominance, the even and odd carbon number predominance coexisting in whole carbon number. In papers, the characteristics of a nalkane coexisting even and odd carbon number predominance and its origin are investigated only. The shortchain nalkanes and longchain nalkanes are characterized by a pronounced odd carbon predominance, with the dominant carbon number of nC15, nC17 and with nC25, nC27, nC29，nC31. And the midchain nalkanes are dominated by even carbon predominance, with the dominant carbon number of nC20 and nC22.A number of biomarkers support sediments deposited in an anoxic, hypersaline lacustrine setting. These include the phytane preference, high gammacerane and the presence of βcarotene and C24tetracyclic terpane. The biomarkers are not homosphere, which shows that salinity and redox is not constant in lake. The nalkanes are mainly derived from algae in lake and macrophytes on land or around edges of the lake. The nalkane distribution patterns of the source rocks and oils studied are believed not to be dependent of the redox in depositional environments and the salinity of water body, but to be associated with original organic matter composition. 