Quantifying denudation rates and sediment recycling of low-relief, high-elevation landscapes using in-situ and meteoric cosmogenic nuclides

Abstract

Quantifying Earth’s surface denudation rates is crucial for estimating sediment flux and its role in regulating global climate change. The inability of in-situ cosmogenic 10Bein to quantify denudation rates in quartz–free environment has prompted the need for a new proxy–the ratio of meteoric 10Bemet to mineral-weathered 9Be in reactive phase (precipitated in or adsorbed onto secondary minerals). This study utilized 10Bein–26Alin, 10Bemet/9Be, and major element analyses of reactive and mineral phases of bedload sediments to infer basin-wide denudation rates and sediment recycling (reworking of deeply buried sediments) in the Three River Source Region (TRSR) of the central Tibetan Plateau. Results from 10Bein-26Alin analysis of bedload sediments and bedrock samples (quartz grain, 250–500 μm) suggest that the sediments underwent burial events since at least 0.54 ± 0.16 million years ago. Combining paleoclimate records in the central Tibetan Plateau, we interpret the “Great Burial” as most likely the result of climate-controlled deglaciation and denudation at the termination of Naynayxungla glaciation during the MIS 13–15 period. This event marks the first widespread deglaciation on the Tibetan Plateau. The 10Bein-26Alin derived paleo–denudation rates range from 4.2-0.8+0.9 to 151-32+37 mm/kyr, consistent with previous 10Bein–derived modern denudation rates of 10–117 mm/kyr in TRSR. These rates show a moderate positive correlation with regional topography, particularly channel steepness, indicating a decrease in both relief and denudation rates from lower to upper streams. This spatial discrepancy is likely due to enhanced river headward incision and active neotectonic activities in the southeast. Denudation rates derived from the 10Bemet/9Be proxy range from 13 to 248 mm/kyr, alongside a chemical weathering intensity ranging from 43 % to 67 %. These denudation rates are strongly correlated with, but about 1.5 times higher than, the 10Bein–26Alin derived paleo–denudation rates from the same watershed. This suggests that the 10Bemet/9Be extracted from fine grains (<64 μm) may reflect a different sediment recycling pattern compared to 10Bein–26Alin in quartz sediments. Alternatively, the 10Bemet/9Be ratio could indicate a mixture of carbonate rock with a high denudation rate and silicate rock with a lower denudation rate, whereas 10Bein–26Alin reflects a single silicate denudation signal.