Provenance and hydrological event records of water-laid sediments at the Sanxingdui site: implications for migration routes and civilizational decline

The evolution of river systems has profoundly shaped the emergence, migration, and decline of ancient civilizations. The Sanxingdui site on the Chengdu Plain, one of the most significant archaeological discoveries of the 20th century, witnessed an abrupt civilizational decline whose causes remain debated. Min River avulsion and the Jintang Gorge damming-backwater event have been proposed as potential triggers, while the migration routes of the Sanxingdui population are also debated. To clarify hydro-environmental influences, this study focuses on the site's core area, including the sacrificial pits and the northern trench, integrating sedimentological, geochemical, and heavy mineral analyses of water-laid sediments with OSL dating results. Results indicate that the site is situated on water-laid Guanghan Clay formed during the middle-late Late Pleistocene, with trench use spanning the entire Sanxingdui civilization period (referring to Phases II ∼ IV of the Sanxingdui site, ca. 4.1∼2.8 ka). Distinct flood events can be identified within the trench sediments, dated to ca. 3.3 ka, with a minimum inundation height of ∼3.5 m and an impact radius approaching 1 km. Since the middle-late Late Pleistocene, the Jian River provenance has remained stable, dominated by felsic metamorphic and igneous rocks derived from the Early Proterozoic Huangshuihe Group and the Middle-Late Proterozoic Pengguan Complex in the central Longmen Mountains, distinct from the Min, Mianyuan, and Shiting Rivers, confirming the Jian River's long-term independence. Therefore, the ca. 3 ka Jintang Gorge damming-backwater event was unrelated to the flood events at Sanxingdui site, and the independent hydrological configuration precludes the possibility that northwestern populations migrated via the Min River valley to the upper Jian River and then reached the Sanxingdui site. Instead, the earliest inhabitants migrated along the upper Fu River basin, established Phase I of the Sanxingdui site (4.8∼4.1 ka), the subsequent incorporation of populations from the Baodun site complex and continued cultural interactions with other regions ultimately gave rise to the flourishing Sanxingdui civilization (4.1∼2.8 ka).