Phytolith-based reconstruction of coastal dynamics in East China: Modern calibration, proxy evaluation, and implications for the Liangzhu Civilization

High-resolution palaeoenvironmental reconstruction is critical for identifying environmental drivers underlying the emergence of early human civilizations. To achieve this, we systematically collected representative native plants and surface sediments from tidal flats and coastal plains along the eastern coast of China. Using these samples, we established robust qualitative and quantitative relationships between phytolith assemblages and sedimentary environments. These relationships were applied to a sedimentary sequence retrieved from a Neolithic Liangzhu cultural site located on the Yangtze Delta coastline. The results show that coastal wetland sediments in East China are dominated by short-cell phytoliths derived from in situ Poaceae vegetation, alongside allochthonous bulliform phytoliths introduced from terrestrial sources and redistributed into the intertidal zone by marine processes. Consequently, the ratio of bulliform to grass short-cell phytoliths (Bull/GSSC) provides a reliable proxy for assessing the marine influence across the coastal plain. Furthermore, surface sediment phytolith assemblages exhibit strong elevation-dependent patterns along an intertidal transect in the Yangtze Delta, enabling the development of transfer functions that link phytolith composition to surface elevation. When applied to the archaeological sedimentary sequence, these transfer functions and Bull/GSSC ratio reveal pronounced interdecadal fluctuations in relative sea level and heightened frequency of extreme storm events around 5.1 cal. kyr BP, indicating increased climatic instability prior to the strengthening of ENSO dynamics in the mid-Holocene. This study therefore highlights in high precision the environmental drivers for the emergence of Liangzhu civilization around 5000 years ago.