Abstract
Prehistoric city sites, as pivotal aspects of early urban evolution, are intricately linked to regional environmental factors such as climate, geomorphology, and hydrology. However, due to the lack of reliable chronologies associated with these ancient sites, there is limited understanding of environmental factors in relation to prehistoric urban centers. This study focuses on the sedimentary records from the southern moat of the Fenghuangzui (FHZ) ancient city site, a representative site in the middle Yangtze River region, integrating a chronological framework and climate proxies such as elemental geochemistry. It reconstructs the evolution of the regional sedimentary environment and the hydrogeomorphology during the mid-late Holocene at the FHZ site, elucidating its interplay with human activities. Key findings include: (1) From 5.5 ~ 4.5 ka BP, elevated CIA, Rb/Sr, and Mn/Ti values indicate a warm and humid climate. The Qujialing culture unified the middle Yangtze River and expanded abroad, building prehistoric cities such as Shijiahe city. The FHZ city was built in the Nanyang Basin at this time to prevent the invasion of northern culture. (2) During 4.5 ~ 3.9 ka BP, decreased CIA and Rb/Sr values alongside rising Saf and Be values signify reduced weathering and a transition to cooler, drier conditions. A flood event of 4 ~ 3.9 ka BP caused the moat of the FHZ city to lose its defensive function. (3) During 3.9 ~ 2.7 ka BP, declining CIA and Rb/Sr values with slight increases in Saf and Be suggest ongoing dry and cool environmental conditions. The FHZ city was abandoned at the end of the Meishan culture. (4) Between 2.7 ~ 1.6 ka BP, rising CIA and Rb/Sr values indicate a return to warmer and more humid conditions. The FHZ site was built to expand the influence of Qujialing culture and protect the Shijiahe city. Taking into account the location of the water system and farming area, the south-facing direction was chosen. After a flood in 4.0 ~ 3.9 ka BP, the FHZ site lost their defense function and were invaded by Meishan culture. In general, our findings suggest that changes in regional hydrology in the context of climate change can trigger upheaval and even collapse of prehistoric societies.