OSL Dating of the River Terraces in the Danxiashan Area of Northern Guangdong Province

　　In the research on the Danxia landform, the study of river terraces, which record the process of landform evolution, is relatively scarce, especially the lack of research on the formation age of related river terraces. River terraces contain information on the river incision process and environmental changes, and conducting terrace chronology studies can help reconstruct the history of river evolution, and further explore the response to climate change.
　　In the Danxiashan area of northern Guangdong, the authors found typical sedimentary characteristics in the river terrace profiles of the Jinjiang River and Lingxi River (a mountain stream), and carried out optically stimulated luminescence (OSL) dating. The dating results show that the Jinjiang T₀, T₁, T₂ terraces and the Lingxi River T₁ terrace were formed at 0.41 ± 0.08 ka, 70.14 ± 6.08 ka, 300.64 ± 14.66 ka, and 18.26 ± 3.22 ka, respectively. The incision times of the Jinjiang T₁ and T₂ terraces correspond to the transition stages of Marine Isotope Stage 5-4 (MIS5-MIS4) and MIS9-MIS8, respectively. This indicates that during the transition from cold to warm periods, the incision capacity of the Jinjiang River significantly exceeded the sedimentation flux, leading to the formation of the earlier floodplain sediments and the underlying wide valley floor into terraces. The Lingxi River T₁ terrace was formed during the MIS2 period, which may be related to the characteristics of the mountain stream (narrower valley) and the influence of seasonal runoff.
　　Based on the relationship between the gravel layer and the height and age of terrace surface, we have estimated that the minimum incision rates of the Jinjiang River during the two time periods of ~300 ka to ~70 ka and ~70 ka to the present are (0.05±0.00) mm/a and (0.22±0.02) mm/a respectively. There are two main reasons for the significant acceleration of the incision rate: first, the alternating effects of river erosion and accumulation, which leads to a slowdown in the incision rate over time; second, the rate of cutting through alluvial-pluvial deposits is faster than that of cutting through bedrock. These incision rate data provide important evidence for the restoration and reconstruction of the evolution process of Danxia landform.