Multi-proxy evidence of environmental change related to collapse of the Liangzhu Culture in the Yangtze Delta, China

The Liangzhu Culture (5300-4300 cal. a BP) has been regarded as the culmination of the Neolithic Age in the Yangtze Delta and as an archaic state. However, the reason behind the collapse of the Liangzhu Culture remains controversial. Some scholars attributed it to social conflicts or foreign invasions, while others suggested that environmental deterioration, such as cold episodes, inundation and palaeo-typhoon events, disrupted the civilization. Notably, the yellowish silty sediments widely overlying the Liangzhu group sites have been presumed to be one of the vital clues to resolving these issues. The process and cause of their formation are key to understanding the decline in Liangzhu Culture. In this study, two typical profiles composed of the Liangzhu cultural layer and yellowish silty sediments were collected in the Liangzhu Ancient City. Multiple proxies, including pollen, phytoliths and diatoms, along with radiocarbon and optically stimulated luminescence dating and synthesized geochemical evidence from different sediments, were applied to reconstruct ecological and hydrological changes and discuss their linkage to cultural collapse. The regional ecology was typical freshwater wetlands during 4800-4400 cal. a BP, which facilitated rice farming and large-scale architectural engineering in Liangzhu Ancient City. Evidence from microfossils and dating of the yellowish silty sediments indicated that Liangzhu Ancient City was significantly affected by seawater after abandonment during 4300-3400 cal. a BP. Furthermore, geochemical evidence, including trace element and Sr-Nd isotopic compositions, suggested that the primary provenance of the yellowish silt was a mixture of sediments from the Qiantang River, East China Sea, Yangtze River and Yellow River, which had been transported to Liangzhu Ancient City by the Yellow Sea Coastal Current and a marine transgression. Therefore, based on evidence from archaeological sites and numerical simulation in the Yangtze Delta, it was supposed that the short-term accelerated relative sea-level rise at approximately 4400 cal. a BP caused a marine transgression around Taihu Lake, formed a large range of yellowish silty sediments, destroyed rice farming production, and ultimately led to the collapse of the Liangzhu Culture.