中文摘要：

选自长江口F2-F5站住的4个表层沉积物及其粒度分级（1～8Ф）样品，经过孢粉相和热解检测，探讨有机质特征及其在碳循环中的命运。未分级样品的孢粉相主要由木质组织、丝炭和黑团块组成，显示陆地输入有机质的贡献巨大。样品分级后，孢粉相面貌发生显著变化。细粒的8函中无定形为主，其他粒级（2～7Ф）中主要由结构有机质组成。细粒的8函中具有高HI、高S2和低Tmax值的特点，表明来源于水生生物；而其他粒级（2～7Ф）有机质显示了高等植物来源和充分氧化降解的特性。在远离河口的F4和F5站位，细粒的8空中无定形有机质对TOC贡献约近70%；在河口附近F2和F3站位，粗粒的（2～7Ф）中颗粒有机质聚集，TOC分配比较均衡。细粒的8函中无定形有机质，受粘土矿物的保护可有效抵御微生物及氧化降解，能迅速地絮凝和沉降，缩短了从生物圈、水圈到岩石圈的进程，致使碳循环周期延长；而粗粒的（2～7Ф）中陆地输入的颗粒有机质，已历经充分的氧化降解，可以长期保存在沉积物中，碳循环周期最长。因此，关注沉积物中有机质与粘土矿物的相互关系以及对碳循环周期的影响，这可能是开启未知碳汇之谜的一把“金钥匙”。

英文摘要：

Palynofacies and pyrolysis were applied to four surface sediment samples （F2 - F5 ） from the Changjiang estuary and their 1 - 8Ф particle size fractions to discuss the characteristics of organic matter （OM） and their fate in carbon cycle. The palynofacies of bulk samples are mainly comprised of woody tissue, charcoal, and black mass OM, which indicates a large contribution of terrestrial organic matter input. After fractionation, the feature of palynofacies changed significantly. Fine particle size fraction （80） dominated in amorphous OM, while other fractions （2- 70） were comprised of structural OM. Fine particle size fraction （8Ф） was characterized by high HI, S2 and low Tmax value, which suggests an aquatic organic matter origin. However, the OMs of other size fractions （2 - 7Ф） were characterized by terrestrial organic matter input and great oxidative degradation. In samples of F4 and FS, which are far from the Changiiang estuary, about 70% of the TOC was contributed by fine particle size fraction （8Ф）,while the TOC is homogeneous in different size fractions of samples of F2 and F3 which are near the estuary. The amorphous OM in fine size fraction （8Ф） was protected by clay minerals from biodegradation and oxidative degradation. These OM flocculate and precipitate rapidly, and shortened the process from biosphere, hydrosphere to lithosphere. As a result, this may prolong the period of carbon cycling. The OMs in other fractions （2 - 7Ф） underwent oxidative degradation and were preserved in sediments with the longest period of carbon cycling. Consequently, the relationship between sedimentary OM and clay mineral and their influence on the time of carbon cycling should be concerned. This may help us to get some future understanding of carbon cycle which is still uncertain.