川西雅砻江普巴绒段晚更新世早期河流阶地与相关沉积的发育特征、年代约束及其构造气候意义OA

In Yajiang County,western Sichuan Province,six levels of river terraces have developed along the mainstream area of the Yalong River in Pubarong Township,with red clay covering the terraces.Field investigations were conducted on the development characteristics of the river terraces and the overlying red clay.This study investigates the development characteristics of these terraces and the overlying red clay through field surveys,supplemented by optically stimulated luminescence(OSL)dating,pollen analysis,and grain size analysis.The aim is to discuss the climatic and environmental conditions during terrace formation and to determine the genesis of the overlying red clay.The evolution history of the Yalong River valley in the study area was clarified,with the main findings as follows:(1)The terraces in Pubarong Township are all pedestal terraces,standing 10-189 m above the river level.The T2 and T3 terraces formed during the last interglacial period,with ages of(87.7±4.1)ka and(101.5±4.8)ka,respectively,indicating a valley incision rate of approximately 2.03-2.42 m/kyr.The vegetation during the terrace formation was sparse grassland dominated by herbaceous plants.(2)The loess covering the terraces was deposited around(70.3±3.4)ka to(70.0±2.9)ka and represents wind-blown loess typical of the western Sichuan Plateau under a warm and humid climate.The loess material was derived from multiple sources,and locally,it has the characteristics of being transported and accumulated along slopes in the later stages.(3)During the laterization,vegetation shifted to forest-dominated communities.Climatic fluctuations during the last interglacial period were the key to triggering river incision and terrace formation.The transition from the last interglacial to glacial climate was an important factor in promoting loess deposition in the region.