Holocene Sedimentary Evolution And Its Influence On The Development Of Neolithic Culture In The Yaojiang-Ningbo Coastal Plain

The muddy coast is an important area with large population and developed economy in modern society.It was also the important area for the Neolithic settlements.The muddy coast is very sensitive to climate and sea level changes and associated marine hazards.Investigation of the relationship between Neolithic cultures and environmental change is useful for the preparation of climate challenge in present day.Yaojiang-Ningbo Plain not only has the famous Hemudu Culture at home and abroad,but also has recently found the Jingtoushan site buried 5-10 m below the surface as a shell-mound site.This study takes Yaojiang-Ningbo Plain as an example and collected four sediment cores（CC,ZF,XY,and DJQ）there.Lithology observation,AMS ¹⁴C dating,grain size analysis,and identifications of foraminifers and bioturbation were carried out.Together with collected core data,this study tends to reconstruct the Holocene sedimentary environmental evolution and to discuss the response of hydrological and morphological environments to the sea level change and their linkage to the evolution of Neolithic culture.Main conclusions are obtained as follows:（1）The Holocene evolution of sedimentary environment in the Yaojiang-Ningbo Plain was mainly controlled by the sea level change and has evolved from coastal marsh to muddy embayment and coastal plain.The semi-closed Ningbo embayment was formed as a result of rapid sea-level rise in the early Holocene.The embayment was open to Hangzhou Bay due to the sea-level rise at ca.7.6 ka.It was then rapidly infilled after 7.2 ka when the sea level tended to be stable and a large reduction in the accommodation space occurred.Only local areas such as the southeast Ningfeng Plain evolved into coastal marsh until after ca.6 ka.（2）The analyses of lithology,grain size,and foraminifer indicate that marine invasion and hydrological condition strengthened in the paleo-embayment at ca.8.8ka as a response to the accelerated sea-level rise and increased extreme events.The sediments coarsened again,along with the increase in the percentage of thick-and-big-shelled shelf foraminiferal species Cavarotalia annectens and Ammonia compressiuscula at ca.7.6 ka,indicating the acceleration of sea-level rise at that time.（3）The sedimentation rates recorded in numerous cores were high in the paleo-embayment during the early to mid-Holocene and reduced largely after ca.7 ka,which is consistent with the sea level change.Such consistent change indicates that the sediment supply was rich as being close to the large river mouth which can keep up with the accommodation space created by the sea-level rise,and the semi-enclosed embayment is beneficial for trapping of the fine-grained sediments supplied by tides and longshore currents.（4）The shell mound at Jingtoushan site was formed during the period of slowed sea-level rise at ca.8.2-7.8 ka.Such sea level change is beneficial for the aggradation of tidal flat and collection of aquatic resources.The termination of cultural deposition at ca.7.8 ka agrees with the obvious reduction in both intensity and size of the bioturbation,indicating that the resource carrying capacity may have been overloading before 7.8 ka in the small paleo-embayment.Furthermore,the acceleration of sea-level rise at ca.7.6 ka possibly explains the interruption between Kuahuqiao and Hemudu Cultures.The rapid formation of coastal plain at ca.7.2 ka as a response to the stable sea level provided beneficial resources and environment for the development of Hemudu Culture.