Diatom assemblage since late Pleistocene in the east coast of Lingdingyang Bay and its environmental implications

Based on the distribution pattern of diatom in the borehole of sz17QZ-20-3 of Lingdingyang Bay, with the support of dating, lithology and grain size distribution data, the paleoenvironment evolutionary history since late Pleistocene of this area is reconstructed. According to the change in lithology and grain size of the sediments, a vertical sequence consisting of river bed facies-drowning valley bay facies-beach facies-alluvial facies upwards was established for the interval of 23.6～11.0 m of Late Pleistocene. The presence of Ethmodiscus Rex fragments of marine species in the variegated clay layer indicates the cyclic transgressive and regressive sequences of the late Pleistocene. Early Holocene transgression reached the research area around 9000 cal. aBP, the diatom content of marine species rapidly increased, and the coastal plain facies was rather developed. The highest sea level was reached around 8000 cal. aBP, with the highest content of diatom of marine species. The sea level was falling after a period of stability and shallow marine deposits dominate; The Middle-Late Holocene or the interval of 4.2～0 m indicates a regressive period dominated by estuarine facies. The sharp increase in marine species at 4.4～4.2 m horizon in addition to shell debris at 4.4～4.6 m horizon of Middle Holocene indicates storm surge events; the diatom abundance in surface sediments at 0.3～0 m horizon of Late Holocene is unusually high under the influence of human activities.