四川剑门关侏罗—白垩系红层分子化石的古环境和古气候意义

利用气相色谱－质谱仪从四川剑门关侏罗－白垩系红层中检测出包括正构烷烃、类异戊二烯烃、长链三环萜、霍烷及甾烷等系列分子化石。分析了这些分子化石的分布特征及其来源，利用分子化石的多项参数（如w(C21^-)/w(C22^ ),w(Pr)/w(Ph),w(Pr)/w(nC17),w(Ph)/w(nC18)，伽马蜡烷指数、甾烷等）对沉积环境的盐度、氧化－还原条件、陆相标志等方面作了探讨。这些分子化石参数证实中侏罗世－早白垩世，剑门关－带的沉积环境应为低盐度淡水、弱氧化的陆相沉积环境，所研究的陆相样品高碳数正构烷烃均以本植物有关的C27，C29为主峰，未出现草本植物的C21主峰，反映了研究区总体格局是一种以木本植物占绝对优势、温暖湿润的气候环境，与红盆发育的气候条件吻合，充分体现了分子化石在恢复古环境、古植被和古气候方面有极大潜力。

MOLECULAR FOSSILS AS INDICATORS FOR PALEOENVIRONMENT AND PALEO-CLIMATE FROM RED CLASTIC ROCKS OF MIDDLE JURASSIC-EARLY CRETACEOUS IN JIANMENGUAN, SICHUAN BASIN OF CHINA

Series of molecular fossils, including n-alkanes, extended tricyclic terpanes, hopanes and regular steranes, have been detected from the red clastic strata of Middle Jurassic-Early Cretaceous in Jianmenguan profile, Sichuan basin in China. These molecular fossils are supposed to be derived from higher plants and aquatic organisms. Their parameters such as low gammaceran abundance, relative higher w(Pr)/w(Ph) and the dominance of C27-ethylcholestane suggest the occurrence of a limnetic, non-reductive continental environment in the study area during Middle Jurassic and Early Cretaceous. C27 and C29 n-alkanes, believed to be related to woody plants, constitute the main high-carbon number n-alkanes in the studied samples, while C31 n-alkane, supposed to be the main n-alkane in herbal plants, does not prevail over C27 and/or C29 n-alkanes in the samples. This suggests the flourishing of woody plants other than grassy plants at that geological time. This kind of vegetation further indicates the existence of a warm and humid climate from Middle Jurassic-Early Cretaceous, a kind of climate favorable for the development of the red basin. This investigation of the red sedimentary rocks shows that the molecular fossils have a high potential in recovering the paleoenvironment, paleo-vegetation and palaeo-climate.