Sea-level changes and human economic development in the northern flank of the Yangtze River Delta during the Middle to Late Holocene

Abstract

The environmental dynamics in coastal regions are inevitably influenced by fluctuations in sea levels and human interventions. Evidence derived from archeological site remains and sediment cores indicates that sea-level change has been the primary driving force behind the continuous relocation of human settlements since the Holocene epoch. However, the understanding of the Holocene land formation process and its relationship with human activities in the northern flank of the Yangtze River Delta remains limited. The Guoqing Temple, located in southwest Juegang and serving as a hub for sea salt production during the Sui and Tang Dynasties, was established in the Tang Dynasty and served as one of the pivotal points along the Maritime Silk Road. A sedimentary core was obtained in close to the Guoqing Temple, and the sedimentological and micropalaeontological data were analyzed to investigate the process of sedimentary evolution from marine to terrestrial environments, as well as the environmental factors facilitating the development of the salt industry. Analysis results explained that: Between 6360 and 1750 cal yr BP, the study area was situated in a shallow sea on the outermost periphery of the sandbank, with a maximum water depth of 20 m. After 1750 cal yr BP, it underwent a transition to a supratidal low-salinity shallow marsh environment that continued to be influenced by marine conditions. The climate in the study area is primarily influenced by the Asian monsoon: Before 3000 cal yr BP, the overall climatic conditions were characterized by warm and humid conditions; After 3000 cal yr BP, climate stability prevailed in the region. Meanwhile, due to the newly formed wetlands that facilitated extensive salt production, economic shifts toward southern regions, and reforms in salt laws during the Tang Dynasty, Juegang emerged as a flourishing commercial trade hub and a prosperous center for Buddhist culture.