从泌阳凹陷下第三系湖相碳酸盐岩中检测到了丰富的并以成对分布为特征的三环二萜烷。整个碳酸盐岩剖面中有机质类型均以Ⅰ型为主，成对分布的三环二萜烷中１３α（Ｈ），１４α（Ｈ）异构体向热稳定性更高的１３β（Ｈ），１４α（Ｈ）异构体转化，其含量随埋深的增加而减少。据此提出可以三环二萜烷热演化参数ＴＣＴ，即αα构型向βα构型转化率来表征未成熟和低成熟生油岩中有机质的热演化程度。 Tricyclic diterpenes, characterized by a pairwise distribution, were detected from the Paleogene lacustrine carbonate rocks in the Biyang depression. The type of organic matter in the whole carbonate rock profile is type I. The 13α (H) and 14α (H) isomers of the tricyclic diterparaines in pairs distribute toward the more thermostable 13β (H) 14α (H) isomer conversion, its content decreases with increasing depth. It is proposed that the thermal evolution of organic matter in immature and low mature source rocks can be characterized by TCT, which is the transition from αα to βα configuration.