Upper Pleistocene-Holocene geomorphic changes dictating sedimentation rates and historical land use in the valley system of the Chifeng region, Inner Mongolia, northern China

This study focuses on the late Quaternary landscape evolution in the Chifeng region of Inner Mongolia, China, its relations to the history of the Pleistocene-Holocene loess accumulation, erosion and redeposition, and their impact on human occupation. Based on 57 optically stimulated luminescence (OSL) ages f loess sediments, fluvial sand and floodplain deposits accumulated on the hill slopes and floodplains, we conclude that during most of the Pleistocene period the region was blanketed by a thick layer of aeolian loess, as well as by alluvial and fluvial deposits. The loess section is divided into two main units that are separated by unconformity. The OSL ages at the top of the lower eddish loess unit yielded an approximate age of 193 ka, roughly corresponding to the transition from MIS 7 to 6, though they could be older. The upper gray loess unit accumulated during the upper Pleistocene glacial phase (MIS 4-3) at a mean accumulation rate of 0·22 m/ka. Parallel to the loess accumulation on top of the hilly topography, active fans were operating during MIS 4-2 at the outlet of large gullies surrounding the major valley at a mean accumulation rate of 0·24 m/ka. This co-accumulation indicates that gullies have been a long-term geomorphic feature at the margins of the Gobi Desert since at least the middle leistocene. During the Holocene, the erosion of the Pleistocene loess on the hills led to the burial of the valley floors by there deposited sediments at a rate that decreases from 3·2 m/ka near the hills to 1-0·4 m/ka1 in the central part of the Chifeng Valley. This rapid accumulation and the frequent shifts of the courses of the river prevented the construction of permanent settlements in the valley floors, a situation which changed only with improved man-made control of the local rivers from the tenth century AD.