Reconstruction of the paleoenvironmental context of Holocene human behavior at the Fenghuangzui site in the Nanyang Basin, Middle Yangtze River, China

Geomorphological research at archaeological sites reveals that environmental factors, such as geomorphology and hydrology, play a crucial role in understanding changes in site layout and cultural processes. However, due to the lack of reliable chronologies, there is limited understanding of environmental factors in relation to archaeological site. This study focuses on the sedimentary records from the southern moat of the Fenghuangzui (FHZ) 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 5.6–4.5 ka BP, elevated chemical index of alteration (CIA), Rb/Sr, and Mn/Ti values indicate a warm and humid climate. The Qujialing culture unified the middle Yangtze River and established regional central settlements such as Shijiahe site, and then expanded to the north. The FHZ site was built in the Nanyang Basin at this time to prevent the invasion of northern culture. (2) During 4.5–4 ka BP, decreased CIA and Rb/Sr values alongside rising secondary aluminum factor (Saf) and dealkalization coefficient (Bc) 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 site to lose its defensive function. (3) During 4–2.7 ka BP, declining CIA and Rb/Sr values with slight increases in Saf and Bc suggest ongoing dry and cool environmental conditions. The FHZ site 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 settlement. Taking into account the location of the water system and farming area, the south-facing direction was chosen. 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.