Sedimentary records of mid-Holocene extreme storm events and Neolithic cultural response in the Yaojiang-Ningbo Plain, East China

The Yaojiang-Ningbo coastal plain in East China is naturally vulnerable to salinity intrusion. At around 5.3 ka, the study area experienced a period (the 5.3 ka extreme storm period) when extreme storm events and associated salinity intrusions were especially frequent. Sedimentary records are widely distributed in the plain but have thus far not been systematically amalgamated, constraining interpretation of the impacts of these extreme storms on prehistoric coastal communities. Here we present a multi-proxy analysis of the chronology, sedimentology, and geochemistry of a profile containing records of the 5.3 ka extreme storm period from a newly excavated Neolithic site, Hukengji, in the Yaojiang-Ningbo plain. Results of the paleoenvironmental reconstruction evidences a tidal marsh environment at the site at ca. 6.0 ka, which was exposed to salinity intrusions at ca. 5.3 ka and river flooding at ca. 5.1 ka. Through comparison with other sedimentary records in the region, we show that the 5.3 ka extreme storm period in the Yaojiang-Ningbo Plain extended from ca. 5.4 ka to ca. 4.9 ka, with two peaks at around 5.3 ka and 5.1 ka. Communities of the Hemudu Culture Period IV adapted to this phase of coastal flooding, for example, by constructing artificial mounds. However, the effects of the extreme hydroclimatic events during the 5.3 ka extreme storm period led eventually to the Hemudu Culture being replaced across the region by the more complex and socially stratified Liangzhu Culture from around 5.1 ka onwards.