干旱区生态环境知识资源中心

Chronometric and sedimentological data generated from the exposed Quaternary sequences of the Orsang River basin indicate close correspondence between the environmental changes and fluvial aggradation. The oldest and regionally extensive fine silty-clay occurring at the base of the successions is dated to >97 ka suggesting prevalence of high sinuosity suspended load fluvial regime. Its stratigraphic position suggests that the deposition occurred during the enhanced southwest monsoon corresponding to the Marine Isotopic Stage-5 (MIS-5). The gravel deposits that overlie provide an age of similar to60 ka indicating dominance of braided system (MIS-4) during the reduced southwest monsoon. The pluvial interstadial (MIS-3) is represented by flood plain facies that was deposited under the persistent fluvial system strengthened by enhanced southwest monsoon and assigned ages ranging between 50 and 30 ka. An extensive aeolian sand sheet that blankets the topography, is luminescence dated to 21 ka suggesting the onset of Last Glacial Maximum in the Orsang River basin.