Microscale fluvial landscape evolution and its impacts on early human settlement at the Shangshan cultural site in the upper Qiantang region, eastern China

Abstract

Detailed reconstruction of the evolution of fluvial landscapes is important for understanding early human settlement where habitats may be influenced by local river processes. Based on high-resolution geomorphological mapping and sedimentological analyses from five trenches, we reconstructed the geomorphic processes before and after the Shangshan period (10–8.5 ka BP) at the Pujiang Shangshan site in the upper Qiantang region, home to the earliest known rice agricultural population in eastern China. Excavation of paleochannel sediments and analysis of geomorphological features revealed that a migrating river channel and floodplain began developing at least ca. 16 ka cal BP, following extensive eolian sedimentation. By this time, terraces (Q₂) formed by the accretion of middle Pleistocene alluvium, had been established, providing ideal Shangshan settlement locations. The Q₂ terrace at that time was 5–8 m above the riverbed. Moreover, the identification of later Holocene, small-scale (1–2 m) terraces (Q₄), and sedimentary evidence indicate that after the Shangshan occupation, the floodplain experienced prolonged aggradation and channel migration. These river activities greatly altered the fluvial landscapes, reducing both the dimensions of the occupied terrace and its height difference from the riverbed. Our reconstruction reveals that two major aggradations occurred during the late Pleistocene and middle to late Holocene, with dominant lateral accretion observed in the fluvial plain construction of the upper Qiantang region. The aggradational river systems, characterized by wide floodplains and elevated Q₂ terraces, provided favorable conditions for rice cultivation and living spaces for early humans, which likely contributed to the emergence of a sedentary agricultural society in eastern China. These results emphasize the importance of river processes in shaping human settlement patterns in the lower Yangtze region and offer insights into Holocene human-environmental relationships. We suggest that similar methodologies can be employed to reconstruct geomorphic processes at other riverine archaeological sites.