OSL dating of the river terraces and climatic evolution in the Danxiashan Global Geopark, Northern Guangdong, China

Objective In the Danxia landform area, numerous river terraces have developed, yet research on them has been relatively limited, particularly concerning their dating. River terraces serve as valuable records of the incision processes of rivers and associated environmental changes. Investigating the chronostratigraphy of these terraces enhances our understanding of Danxia landform evolution, reconstructs river history, and explores responses to climate change.

Methods In the Danxiashan area of northern Guangdong, the river terrace profiles of the Jinjing River and Lingxi River (intermountain streams) exhibit sedimentary characteristics of a river "dual structure".

Results Optically stimulated luminescence (OSL) dating reveals deposition ages for the T₀ floodplain, T₁ and T₂ terraces of Jinjing River, as well as the T₁ terrace of Lingxi River, at 0.4±0.1 ka, 70.1±6.1 ka, 300.6±14.7 ka, and 18.3±3.2 ka, respectively. The sedimentation periods for the T₁ and T₂ terraces of Jinjing River align with transition phases of deep-sea oxygen isotope stages 5 to 4 (MIS5-MIS4) and 9 to 8 (MIS9-MIS8), respectively. This suggests that during the shift from warmer to cooler periods, the sediment flux of the Jinjing River exceeded its transport capacity, resulting in ongoing terrace deposition. Subsequent climatic shifts led to valley incision, forming terraces from earlier floodplain deposits and the underlying broad valley surface. The T₁ terrace of Lingxi River emerged during MIS2, during which the intermountain stream carried a significant amount of sediment. By analyzing the relationship between the gravel layers of the terraces, their heights, and their ages, we estimated the minimum incision rates for the Jinjing River during two periods: 300 ka to 70 ka and 70 ka to the present, at 0.05±0.002 mm/a and 0.22±0.02 mm/a, respectively.

Conclusions The notable increase in incision rate may be attributed to three primary factors: first, the alternation between river erosion and sediment accumulation, leading to a generally low long-term average incision rate; second, the rate of river cutting through alluvial deposits surpassing that through bedrock; and third, the increased climate variability since the last glacial period, which has amplified river erosion rates. These incision rate data provide crucial insights for reconstructing the evolution of Danxia landforms.