Late Holocene asymmetric desert evolution in the mountain-basin geomorphological system of the Tianshan Mountains

The ecological and socioeconomic systems of dryland are especially vulnerable to climate change and are significantly impacted by desertification. As one of the largest dryland regions and a major global dust source， the history of desert evolution in arid Central Asia has been extensively researched. Previous studies have indicated that the formation times of the Bayanbulak sandy land and the Yili Basin desert were asynchronous within the complex mountain-basin geomorphological system of the Tianshan Mountains. However， it is unclear whether differences exist in the formation and evolutionary mechanisms of these two deserts. In this study， we analyze the formation and evolutionary processes and mechanisms of the Yili Basin desert and the Bayanbulak Sandy Land， using magnetic and grain size analyses of sedimentary sequences， combined with optically stimulated luminescence and accelerator mass spectrometry ¹⁴C dating. Our findings indicate that soil formation in the Bayanbulak Sandy Land intensified with increasing Holocene moisture， suggesting that fixation of desert in this region was primarily driven by climatic factors. However， the desert in the Yili Basin began to develop during the late Holocene， a period characterized by increased moisture and strong wind activity. This suggests that climate change was not the primary driving factor responsible for the formation of this desert. The desert sediments in the Yili Basin are closely related to fluvial sediments， indicating that fluvial sediments provide material sources for the desert. We propose that geomorphological changes caused by fluvial downcutting due to increased moisture supply were the key to desert formation in this area during the late Holocene. Strong surface wind erosion mobilizes exposed floodplain sediments， providing material sources for desert formation. Our findings provide new insights into the formation and evolution of deserts within the complex geomorphic systems.