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man">Source rocks from a Tertiary inland lake in the Qaidam Basin man’; mso-hansi-font-family: ’times new roman’">(man">west,Chinaman’; mso-hansi-font-family: ’times new roman’">)man"> were analysed for ar- omatics using capillary gas chromatography-mass spectrometry man’; mso-hansi-font-family: ’times new roman’">(man">GC-MSman’; mso-hansi-font-family: ’times new roman’">)man">. The triaromatic members of the new series, phenylnaphthalenes man’; mso-hansi-font-family: ’times new roman’">(man">PhNsman’; mso-hansi-font-family: ’times new roman’">)man"> and terphenyls man’; mso-hansi-font-family: ’times new roman’">(man">TrPsman’; mso-hansi-font-family: ’times new roman’">)man">, are found in different types of source rocks. The isomeric composition of phenylnaphthalenes and terhenyls was found to depend on thermal ma- turity. In the samples with lower maturity abundances of 1-PhN and o-TrP are higher. Increase in sample maturity is indicated by an increase in the relative abundance of 2-PhN as well as m-TrP and p-TrP. Three thermal maturity parameters of the organic matter based on the relative abundances of the PhN and TrP i- somers are proposedman’; mso-hansi-font-family: ’times new roman’">:man"> PhNR=2-PhN/1PhN,TrPl=p-TrP/o-TrP,and TrP2= man’; mso-hansi-font-family: ’times new roman’">(man">m-TrPman’; mso-hansi-font-family: ’times new roman’">+man">p-TrPman’; mso-hansi-font-family: ’times new roman’">)man">/o-TrP. In general their values are positively correlated with vitrinite reflectance fRoman’; mso-hansi-font-family: ’times new roman’">)man"> in a range of 0. 47%-1. 32%, While correlation of the conventional biomarker maturity parameters man’; mso-hansi-font-family: ’times new roman’">(man">C29 man’; mso-hansi-font-family: ’times new roman’">αααman"> sterane -20S/man’; mso-hansi-font-family: ’times new roman’">(man">20Sman’; mso-hansi-font-family: ’times new roman’">+man">20Rman’; mso-hansi-font-family: ’times new roman’">)man">, C31man’; mso-hansi-font-family: ’times new roman’">αβman"> hopane 22S/man’; mso-hansi-font-family: ’times new roman’">(man">22Sman’; mso-hansi-font-family: ’times new roman’">+man">22Rman’; mso-hansi-font-family: ’times new roman’">)man">,MPI1 ratioman’; mso-hansi-font-family: ’times new roman’">)man"> are less apparent with vitrinite reflectance froman’; mso-hansi-font-family: ’times new roman’">)man"> in a range of 0. 92%-1. 32%. So the new parameters perhaps are effective reflecting degree of thermal evolution of or- ganic matter in the mature-highly mature stage.