Tricyclic aromatic diterpanes found in the Tertiary sediments and their geochemical significance

One monoaromatic tricyclic diterpane and two aromatic tricyclic diterpanes were found in three Iow-maturity source rocks and five crude oils of the Tertiary Shahejie Formation in ShengliOil Field. The compounds found include C19H28 (m/z 145, M+ 256) ring-C monoaromatic tricyclic terpane, C17H2o (m/Z 209, M+ 224) and C18H22 (m/z 223, M+ 238) rings-B,C diaromatic diterpanes.The results show that these compounds are biomarkers of immature organic matter with a stability sequence of C18H22>C17H20>C19H28. The cleavage of ring-D of pentacyclic triterpanoids, such as oleanene, hopene, fernene, ursene, in the early stage of diagenesis may be one of the origin pathways of rings-B, C diaromatic tricyclic diterpanes.