Late Cenozoic diagnostic pollen-spore distribution in southern Yangtze Delta Plain: Depositional geomorphological implications
Zhou Yuanjun1, Wang Zhanghua2, Li Xiao3, Xie Jianlei3, He Zhongfa3, Zhao Baocheng3
1 Department of Geography,East China Normal University,Shanghai 200062 2 State Key Laboratory for Estuarine and Coastal Research,East China Normal University,Shanghai 200062 3 Institute of Shanghai Geological Survey,Shanghai 200072
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.
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