The mid- to late Holocene climate changes in the Chengdu Plain based on fluvial–lacustrine sedimentary records

Key words: 
• grain-size end-member modeling /
• 4.2 ka event /
• flood /
• Sedimentary environment /
• Chengdu Plain

Abstract: [Objective] The Chengdu Plain is one of the major birthplaces of Chinese civilization. Reconstructing the environmental evolution of this region during the mid-to-late Holocene is crucial for understanding the environmental context of prehistoric cultural development in the upper reaches of the Yangtze River and for exploring the relationship between global climate change and the sustainable development of human societies. There remains debate regarding the phased characteristics of mid-to-late Holocene climate evolution in the Chengdu Plain and its potential response to the “4.2 ka” climatic event. [Methods] This study establishes a chronological framework based on the AMS 14C dating of the RS-1 core. Grain size end-member modeling, combined with magnetic susceptibility and colorimetric parameters, was employed to reconstruct the sedimentary environmental evolution of the Chengdu Plain during the mid-to-late Holocene. [Results] Five end-member components were extracted from the grain-size data, each reflecting sedimentary characteristics under different hydrodynamic conditions. EM1 represents stable sedimentation formed by distal fluvial suspended load under weak hydrodynamic conditions. EM2 and EM3 correspond to components deposited under stronger hydrodynamic forces, with EM3 reflecting higher transport energy. EM4 and EM5 indicate coarse-grained traction deposits associated with flood events. [Conclusion] The environmental evolution of the Chengdu Plain during the mid-to-late Holocene can be divided into four stages: (1) 4.7–4.4 cal ka BP, characterized by a humid climate with pronounced wet-dry fluctuations; (2) 4.4–4.2 cal ka BP, marked by a transition to slightly cooler and drier conditions, though remaining generally humid; (3) 4.2–3.7 cal ka BP, a period of pronounced climatic instability with frequent flood events; and (4) post-3.7 cal ka BP, during which the climate gradually became more arid. This “dry–humid–dry” climatic pattern indicates a significant regional response to the “4.2 ka event,” with hydroclimatic changes in the area beginning around 4.4 cal ka BP and persisting until approximately 3.7 cal ka BP.