辽西下白垩统义县组单体烃碳同位素组成变化的物源及环境意义  

The effect of source on carbon isotopic composition of individual hydrocabons in Lower Cretaceous Yixian Formation of western Liaoning and its environmental significance

作　　者：李艳[1,2] 宋之光[1] 曹新星[1,2] 王丽[1] 

机构地区：[1]中国科学院广州地球化学研究所有机地球化学国家重点实验室,广东广州510640 [2]中国科学院大学,北京100049

出　　处：《地球化学》2015年第6期571-580,共10页Geochimica

基　　金：国家自然科学基金(40973033)

摘　　要：辽宁西部白垩系义县组三段沉积于火山活动频繁时期,是富含热河生物化石群的重要层段.本文拟对义县组三段四合屯剖面进行了系统的有机地球化学研究,包括总有机碳（TOC）丰度、饱和烃的组成与分布以及单体烃稳定碳同位素组成等分析.结果显示剖面下部（161.5 cm以下）富含化石层段的TOC含量明显高于上部,表明剖面下部生物的发育与生产力较高.饱和烃的组成分布在剖面上具有明显的阶段性变化特征,剖面底部和上部以高碳数正构烷烃占优势,中部以中等碳数正构烷烃占优势.正构烷烃碳同位素组成在-38.6‰～-26.0‰之间,自下而上逐渐呈正偏的趋势.剖面上正构烷烃主峰碳及碳同位素组成的规律性变化可能与古气候环境变化密切相关.伽马蜡烷的普遍检出以及低的姥植比（Pr/Ph＜0.8）表明当时沉积环境为强还原且具一定盐度分层的水体,沉积有机质得到较好保存.此外,根据高等植物叶蜡烷烃碳同位素组成重建的古大气CO2碳同位素组成在-10‰～-3‰之间,自下而上呈逐渐正偏后又回归的特点,反映了频繁的火山喷发活动造成大气CO2浓度变化及其碳同位素组成的偏移效应.The third member of the lower Cretaceous Yixian Formation in western Liaoning was deposited in a period of frequent volcanic activities, which is one of the most important beds for Jehol Biota. A systematic study was carried out by analysing total organic carbon content, composition and distribution of aliphatic hydrocarbons, and carbon isotopic compositions of individual compounds in the sediment samples from an excavated profile of the lower Cretaceous Yixian Formation in western Liaoning. The data show that the lower part （〈161.5 cm） of profile exhibits an obviously higher organic carbon content, indicating that the thriving of organism and a high productivity occur in this stage. The distribution of n-alkanes also shows a regular change through the profile, i.e., the predominance of long-chain n-alkanes occurs in the lower and upper parts of the profile, while the predominance of medium-chain n-alkanes in the middle section. The carbon isotopic compositions of n-alkanes range from -38.6%0 to -26.0%0, and display an upward positive excursion trend in the profile. This isotopic variation might be related to the paleoclimate change during the deposition of the Yixan Formation. The presence of gammacerane and the low Pr/Ph values （〈 0.8） represent a salinity stratified water column associated with anoxic bottom waters, in which the sedimentary organic matter are well preserved. Furthermore, the reconstructed carbon isotopic composition of atmospheric CO2 during the Early Cretaceous is in the range of-10‰ to -3‰ and also displays an upward positive excursion trend, and then returns to normal status at the top of the profile, implying that frequent volcanic activities probably are a major factor resulting in the variations in concentration and carbon isotopic composition of atmospheric CO2.

关 键 词：生物标志化合物 稳定碳同位素组成 火山活动 义县组 早白垩世 

分 类 号：P593[天文地球—地球化学]