Global analysis of in situ cosmogenic <sup>26</sup>Al and <sup>10</sup>Be and inferred erosion rate ratios in modern fluvial sediments indicates widespread sediment storage and burial during transport
<p>Since the 1990s, analysis of cosmogenic nuclides, primarily <span class="inline-formula"><sup>10</sup>Be</span>, in quartz-bearing river sand has allowed the quantitative determination of landscape mass loss rates (hereafter, erosion rates) at a basin scale...
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| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-07-01
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| Series: | Geochronology |
| Online Access: | https://gchron.copernicus.org/articles/7/213/2025/gchron-7-213-2025.pdf |
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| Summary: | <p>Since the 1990s, analysis of cosmogenic nuclides, primarily <span class="inline-formula"><sup>10</sup>Be</span>, in quartz-bearing river sand has allowed the quantitative determination of landscape mass loss rates (hereafter, erosion rates) at a basin scale. Paired measurements of in situ cosmogenic <span class="inline-formula"><sup>26</sup>Al</span> and <span class="inline-formula"><sup>10</sup>Be</span> in sediment are less common but offer insight into the integrated exposure and burial history of sediment moving down slopes and through drainage basins. Prolonged burial (<span class="inline-formula">>10<sup>5</sup></span> years), a violation of assumptions underlying erosion rate calculations, is indicated by higher <span class="inline-formula"><sup>26</sup>Al</span>-based than <span class="inline-formula"><sup>10</sup>Be</span>-based erosion rates due to preferential loss of shorter-lived <span class="inline-formula"><sup>26</sup>Al</span> by decay when quartz is at least in part shielded from cosmic rays.</p>
<p>Here, we use a global compilation of <span class="inline-formula"><sup>26</sup>Al</span> and <span class="inline-formula"><sup>10</sup>Be</span> data generated from quartz-bearing fluvial sediment samples (<span class="inline-formula"><i>n</i>=766</span>, including 117 new measurements) to calculate the discordance between erosion rates derived from each nuclide. We find that over 30 % of samples (<span class="inline-formula"><i>n</i>=234</span>) exhibit discordance (<span class="inline-formula">>2<i>σ</i></span> analytical uncertainty) between erosion rates derived from <span class="inline-formula"><sup>10</sup>Be</span> and <span class="inline-formula"><sup>26</sup>Al</span>, indicating sediment histories that include extended burial during residence on hillslopes and/or in the fluvial system after or during initial near-surface exposure. Physical basin parameters, such as basin area, slope, and tectonic activity, exhibit significant correlation with erosion rate discordance, whereas climatic parameters have weak correlation, allowing us to infer the likelihood of sediment burial during transport in different geomorphic settings.</p>
<p>Paired <span class="inline-formula"><sup>26</sup>Al</span> and <span class="inline-formula"><sup>10</sup>Be</span> analyses in detrital fluvial samples provide a window into watershed processes, elucidating landscape behavior at different spatial scales and allowing a deeper understanding of both sediment routing systems and whether methodological assumptions are violated. Although previous studies have found <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M19" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msup><mi/><mn mathvariant="normal">26</mn></msup><mi mathvariant="normal">Al</mi><msup><mo>/</mo><mn mathvariant="normal">10</mn></msup><mi mathvariant="normal">Be</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="50pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="9ebd76438a11b1dc3bad7ce831cf1b46"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="gchron-7-213-2025-ie00001.svg" width="50pt" height="15pt" src="gchron-7-213-2025-ie00001.png"/></svg:svg></span></span> erosion rate discordance to be common in the world's largest drainage basins, our analysis suggests that such discordance also occurs regularly in basins as small as 1000 <span class="inline-formula">km<sup>2</sup></span>, indicating that sediment storage mechanisms are more complex than suggested by simple floodplain area scaling laws. Moderately sized basins (1000–10 000 <span class="inline-formula">km<sup>2</sup></span>) with low average slopes in tectonically quiescent terrains appear conducive to extended sediment storage; thus, erosion rates from such basins are lower limits due to nuclide decay during storage. We find that sediment sourced from smaller, steeper basins in tectonically active regions is more likely to have similar <span class="inline-formula"><sup>10</sup>Be</span> and <span class="inline-formula"><sup>26</sup>Al</span> erosion rates indicative of limited storage and is thus more likely to provide reliable erosion rates.</p> |
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| ISSN: | 2628-3697 2628-3719 |