Holocene coastal sedimentary evolution and neolithic human adaption in response to sea level changes in the Palaeo-Taihu valley, East China

Abstract

The neolithic human-land relationship in the eastern coastal plain of China, interlinked sedimentary evolution and sea level changes, has been central to numerous studies. Here, we focus on the evolution of the sedimentary environment and its impacts on human activity in the Palaeo-Taihu valley (PTV) within the northern wing of Hangzhou Bay in response to post-glacial sea level rise. We employ multi-proxy analyses (lithology, AMS 14C, grain size, elements, TOC, and microfossil) on a new sediment core (WZ05) of comparatively analyze a series of previous radiocarbon-dated cores. Our results indicate that since the last deglaciation, the sedimentary environment of Core WZ05 has undergone the floodplain, upper tidal flat, estuary, upper tidal flat, coastal marsh, and fluvial plain, respectively. Regional cores comparisons display three stages: (1) A late Pleistocene incised valley (older than 9600 cal yr BP) dominated by terrestrial deposits accompanied by pottery sherds and rice phytoliths revealing that human activity on the floodplain can be dated to ca. 10600-10300 cal yr BP; (2) An early-mid Holocene transgression stage (9600-7800 cal yr BP) resulted from rapid sea level rise, causing widespread seawater inundation of the floodplain which interrupted early human activity. The transgression maximum during 8000-7800 cal yr BP was marked by the highest sedimentation rates and the coexistence of deep and shallow water species of foraminifera, corresponding to the appearance of a semi-enclosed estuary; (3) Finally, mid-late Holocene terrestrial deposits are the response to a slower sea-level rise and the seaward migration of the coast as the sediment supply exceeded sea level rise at 7800 cal yr BP. Tidal flats and coastal marshes dominated the PTV until 6500 cal yr BP, thereafter sediments continue to fill the PTV such that it develops into a subaerial plain. The reappearance of a freshwater environment since ∼ 7600 cal yr BP allowed the recovery of rice cultivation in the region. Saltwater deposits interspersed with terrestrial deposits between 7000-6500 cal yr BP probably reflect marine inundation during storm events and would have depressed rice domestication.