【摘要】 在对长江三角洲南部平原5个钻遇基岩的晚新生代钻孔的地层、岩性、粒度分析的基础上,根据各岩心剖面中湿生、水生植物花粉和外来植物桫椤孢子化石的分布特征,阐述该区新近纪晚期以来沉积地貌环境演变过程,从而为长江演化的研究提供新的思路。结果显示,新近纪沉积物为粗细混杂的洪积扇相,缺乏湿生、水生植物花粉,反映了此时研究区古地势东西高差显著,沉积物具近源、快速堆积的特征。早更新世古地势高差明显减小,沉降中心西移,但沉积物仍然粗细混杂,湿生、水生植物花粉少见,反映该区具山间盆地较封闭的区域性小流域特征;中更新世沉积物粒度普遍较细,蕨类孢子含量增多,湿生、水生植物花粉普遍出现,并零星出现桫椤孢子,反映研究区具开放、平坦的冲积平原特征;晚更新世—全新世沉积物中湿生、水生植物花粉丰富,蕨类孢子含量显著增多,桫椤孢子普遍出现,表明研究区古海拔高度进一步下降,已演变为滨海—河口沉积环境。上述沉积地貌环境演变过程显示,研究区新近纪和早更新世古地势较高,沉积物物源以本地为主,直到中更新世以来才成为能够接受外来物源的低地,这是利用研究区晚新生代沉积物进行物源分析和长江演化研究时必需要注意的。更多还原

【Abstract】 The present study examined the stratigraphy,lithology,and pollen-spore,especially the diagnostic pollen-spores of the wetland plant,aquatic plant and Cyathea from 5 Late Cenozoic boreholes drilled in the southern Yangtze delta plain,aiming to reveal the sedimentary geomorphological evolution since the Neogene and give insight to the studies of the Yangtze catchment evolution.The results demonstrate that the very poorly-sorted,wetland pollen-lacked sediments were formed as alluvial fan in the Neogene,when topography change was prominent and rapid accumulation of adjacent materials occurred.In the Early Pleistocene,significant reduction in palaeo-topography difference occurred and depositional center shifted westward.However,the sediments are still characterized by the mixture of gravel,sand and mud,and the shortage of wetland plant pollen.Hilly basin of regional small catchment is inferred.The sediments of the Middle Pleistocene are characterized by finer grain size,increasing content of spore fossil,and the appearance of wetland plant pollen and fossil spore of Cyathea,indicating an environment of open alluvial plain.Wetland pollen,fossil spore of Cyathea,and content of total spore increase clearly in the Late Pleistocene-Holocene sediments,suggesting a further decline of altitude of the study area,i.e.,a coastal-estuarine depositional environment.The environmental evolution of the study area further suggests that local sediment source prevailed during the Neogene and Early Pleistocene age when hilly geomorphology dominated.Lowland that could receive large amount of Yangtze sediments did not formed until the Middle Pleistocene,which is very important for the studies of provenance and evolution of the Yangtze River by using the Late Cenozoic sediments from the study area.更多还原