基于叶化石气孔及对照性碳同位素的古大气CO2重建

大气CO2是影响环境变迁的主要因素之一，也是深入理解地史时期全球变化的重要参量。在现有的诸多研究方法中，陆生植物叶气孔分析是以往古大气CO2定量恢复的主要手段之一。植物叶化石除解剖特征之外，还保存有少量单体正构烷烃，而其古环境意义长期被低估。相对于围岩的总有机碳而言，由于叶化石单体烃封存于叶片之内，受成岩作用影响较小，且来源明确，对古大气CO2恢复的精度也就相应更高。本项目选取浙东嵊县植物群中枫香Liquidambar、栎属Quercus、润楠Machilus、杉木Cunninghamia等对CO2变化敏感的优势类群，分别对各类群开展叶气孔和对照性的单体烃碳同位素分析，恢复古CO2浓度，并对二者进行交叉验证。此外，火山岩绝对测年显示该植物群的发展延限为1.6ma(10.8-9.2ma)。因此，本项目的实施在确立古CO2研究新方法的同时，也将高精度重建该地史阶段CO2浓度变化的详细过程。

Atmospheric CO2 is one of important factors to influence environmental change as well as an important parameter to understand global change during geological time. Among some current methods, leaf stomatal parameter method is significant for reconstructing quantitatively ancient CO2. In general, well-preserved leaf fossils possess anatomical characters. Besides, n-alkanes are also preserved in leaf fossils. However, the paleoenvironmental significance of n-alkanes was neglected all along. Compared to total organic carbon from surrounding rock, compound-specific hydrocarbons from fossil leaves have higher precision to estimate paleo-CO2 due to the hydrocarbon sealed into fossil leaves that leads to smaller variation affected by diagenesis, as well as clear sources. As a result, in this research the dominant fossil taxa sensitive to CO2 change are chosen from the Late Miocene Shengxian flora of eastern Zhejiang, such as Liquidambar, Quercus, Machilus, Cunninghamia plants, to perform two researches of stomatal features and corresponding compound-specific hydrocarbon. Based on the two researches, paleo-CO2 levels are estimated. After that, cross validation for the two results will be used to determine which method is more feasible. Based on isotopic dating for overlying and underlying basalts, it was presented that the section bearing leaf fossils was deposited during the geological time from 10.8ma to 9.2ma. Consequently, a new method to reconstruct paleo-CO2 levels will be established in this study. Moreover, this research will contribute to reconstruct paleo-CO2 change with high precision during the Late Miocene (i.e., 10.8ma-9.2ma).