Abstract: The five extractive samples from different depths of source rocks of Tertiary brackish-semi brackish lacustrine deposit of Lucan-1 Well in Wunan-Lucaotan area in southwestern Qaidam basin are analyzed using chromatography-mass spectrometry (GC-MS).The terphenyl series (TrP) of aromatic hydrocarbons in it is detected, including o-TrP, m-TrP and p-TrP. The isomeric composition of the TrP is found to have some relations to the thermal maturity of its organic matter. In the low-maturity samples the abundance of o-TrP is higher; with the maturity increasing, the relative abundances of m-TrP and p-TrP are also increased. The thermally stable order is then proposed as follows: m-TrP>p-TrP>o-TrP. It is also indicated that the I_TrP is positively correlated with R o and m(C_29αα-20S/m[C_29αα-20(S+R)]. It is concluded that the I_TrP parameter can be used to classify the maturity of source rocks to some extent.

Key words: Qaidam basin, organic geochemistry, organic matter, thermal evolution, thermal maturity