Sedimentary records of mid-Holocene coastal flooding at a Neolithic site on the southeast plain of Hangzhou Bay, east China

The history and underlying mechanisms of extreme typhoon events during the Holocene on the east China coast are poorly resolved. This study presents an analysis of the chronology, sedimentology, and organic and alkaline-earth metal geochemistry of a profile (T0103W) collected from the Neolithic Xiawangdu site on the Ningbo Plain, east China coast. Through comparison with the chronology and palaeontology of a second profile from the same site, a coastal, tidally influenced fluvial setting is identified as the geomorphological environment which formed at ~5600 cal. yr BP in the context of a stable or falling relative sea level. Infilling or lateral migration of the tidal river occurred along with the outbuilding of the coastal alluvial plain during the Neolithic occupation. Two periods of salinity intrusion are identified, at ~5310–5145 and 4575–4330 cal. yr BP respectively, as indicated by the increase in Sr concentration and Sr/Ba ratios. Based on our multiproxy analysis, we suggest that frequent extreme typhoon events occurred during both periods. In response to the flooding, the Neolithic people either abandoned the low-lying land close to the river channel or retreated to dwellings constructed on earth mounds. The reconstructed history of extreme typhoon incursions on the east China coast is distinct from those of the South China Sea and southwestern Japan and reflects the complexity of typhoon tracks in the northwest Pacific basin in response to fluctuating sea level and climate change.