Growing pattern of mega-dunes in the Badain Jaran Desert in China revealed by luminescence ages

Sand dunes up to 400 m high are common in the Badain Jaran Desert in China, but how and why mega-dunes grow remains unclear. Timing is the most critical to clarify this issue. The chronological data are still limited with only a few 14C ages from carbonate, not the direct age of the dune, and a few thermoluminescence (TL) ages whose unbleachable residual signals may result in uncertainty in age. Optically stimulated luminescence (OSL) dating uses quartz or feldspars and thus directly dates the sands. It could also be completely reset by daylight with no residual signals. We here report for the first time a batch of OSL ages, and discuss the pattern of the mega-dune growth. Field observation showed that wet sand layers could be exposed in the slope surface and could be easily seen due to its wetness and calcareous cement, causing stronger resistance to wind deflation relative to the adjacent sands. Wet sand layers are normally situated on the mega-dune windward slope, and sometimes could even be seen near the top of a mega-dune, with well-preserved original bedding layers, making them the ideal locations for collecting luminescence samples. Our four OSL samples collected from the Barunbaoritaolegai sand mountain (BSM) show that OSL ages are 4.4 ± 0.5, 5.6 ± 0.5, 11.9 ± 0.9, and 125 ± 11 ka, respectively, from top to bottom. These ages are concentrated in the early to middle Holocene and the Last Inter-glaciation (corresponding to MIS 5e). Based on field observation and OSL ages, we propose that the mega-dunes grow mostly during humid periods with water as cementing agents to build up the sands. The issues, such as the source of the water, how the water seeps into the high sand dunes, how the loose sands could build up to mega-height, etc., require further study.