FORMATION OF MODERN YANGTZE ESTUARY AND SEDIMENTARY ENVIRONMENTAL EVOLUTION SINCE THE LAST DEGLACIATION

The present study measured OSL and ¹⁴C ages for late Quaternary sediments in a borehole drilled in the Chongming Island, Yangtze estuary. Lithology, microfossils, and sporopollen were further analyzed to discuss the formation of the modern Yangtze estuary and sedimentary environmental changes since the last deglaciation. The results indicate a lacustrine and marsh environment at the end of mid-Pleistocene. Fluvial facies dominates during late Pleistocene, especially gravel sediments of the riverbed prevailed during the last glaciation. With the sea level rise during the last deglaciation, estuarine and deltaic sedimentary systems developed successively in the study area. The rapid sea level rise during late deglaciation was demonstrated as rich marine microfossils and strong tidal intrusion in the present borehole sediments. Meanwhile, the high sedimentation rate indicates warm and humid monsoon climate and associated plentiful sediment discharge into the estuary during the early Holocene.