Geochemical characteristics of alkaline earth metals in the sediments of Neolithic sites in the eastern Ningshao Plain and implications for the saltwater intrusion

The eastern Ningshao Plain has nurtured rich and splendid Neolithic cultures. However, interruption of the cultural accumulation in different periods has been found in many sites of the study area. To explore the characteristics of variation and mechanism in concentrations of alkaline earth metals extracted with diluted acetic acid (HAc) and to identify regional seawater intrusion events, two Neolithic sites - namely Jingtoushan and Yushan - were chosen for multiple laboratory analyses on AMS¹⁴C dating, organic geochemistry, and alkaline earth metals and the profiles were compared with stratigraphic records of other Neolithic sites in the study areas. Results show that the concentrations of alkaline earth metals Sr and Ca in the HAc leachates are sensitive to saltwater intrusion in coastal lowland, which were thus used as effective proxies for revealing the hydrological environment in the land-sea transition zone. However, change in Ba concentration was much more complex and Ba was generally lower in the mid-Holocene sediments, suggesting that Ba concentration was not only influenced by salinity but also by the amount of local riverine supply. In addition, three regional events of saltwater intrusion in the eastern Ningshao Plain at ca. 6300, 5300, and 4500 cal. aBP in the middle and late Neolithic Age were revealed, and we believe that they were linked to relative sea-level rise or extreme storm events and induced breaks in the accumulation of culture layers.