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首页> 外文期刊>Earth Surface Processes and Landforms: The journal of the British Geomorphological Research Group >Effects of long soil surface residence times on apparent cosmogenic nuclide denudation rates and burial ages in the Cradle of Humankind, South Africa
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Effects of long soil surface residence times on apparent cosmogenic nuclide denudation rates and burial ages in the Cradle of Humankind, South Africa

机译：长土表面停留时间对南非人类摇篮表观宇宙核素剥削率和埋藏年龄的影响

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摘要

In situ cosmogenic nuclides are an important tool for quantifying landscape evolution and dating fossil-bearing deposits in the Cradle of Humankind (CoH), South Africa. This technique mainly employs cosmogenic 10-Beryllium (Be-10) in river sediments to estimate denudation rates and the ratio of 26-Aluminium (Al-26) to Be-10 (Al-26/Be-10), to constrain ages of sediment burial. Here, we use Be-10 and Al-26 concentrations in bedrock and soil above the Rising Star Cave (the discovery site of Homo naledi) to constrain the denudation rate and the exposure history of soil on the surface. Apparent Be-10-derived denudation rates obtained from pebble- to cobble-sized clasts and coarse-sand in soil (on average 3.59 +/- 0.27 m/Ma and 3.05 +/- 0.25 m/Ma, respectively) are 2-3 times lower than the bedrock denudation rates (on average 9.46 +/- 0.68 m/Ma). In addition, soil samples yield an average Al-26/Be-10 ratio (5.12 +/- 0.27) that is significantly lower than the surface production ratio of 6.75, which suggests complex exposure histories. These results are consistent with prolonged surface residence of up to 1.5 Ma in vertically mixed soils that are up to 3 m thick. We conclude that the Be-10 concentrations accumulated in soils during the long near-surface residence times can potentially cause underestimation of single-nuclide (Be-10) catchment-wide denudation rates in the CoH. Further, burial ages of cave sediment samples that consist of an amalgamation of sand-size quartz grains could be overestimated if a pre-burial Al-26/Be-10 ratio calculated from the surface production is assumed. (c) 2019 John Wiley & Sons, Ltd.
机译：原位宇宙中核素是一种重要的工具，用于量化南非人类（COH）摇篮的景观演化和延迟化石储存。该技术主要采用河沉积物中的宇宙原性10-Beryllium（BE-10），以估计剥蚀速率和26-铝（Al-26）的比例（Al-26）（Al-26 / Be-10），以约束沉积物埋葬。在这里，我们在升起的星洞穴（Homo Naledi的发现位点上方的基岩和土壤中使用Be-10和Al-26浓度，以限制表面上土壤的剥蚀率和曝光史。从卵石至鹅卵石大小的碎屑和土壤中粗砂获得的表观BE-10衍生的剥去率（平均为3.59 +/- 0.27 m / mA和3.05 +/- 0.25 m / mA）是2-3比基岩剥削率低的时间（平均为9.46 +/- 0.68米/ mA）。此外，土壤样品产生平均Al-26 / BE-10比率（5.12 +/- 0.27），显着低于6.75的表面产生比，这表明复杂的暴露历史。这些结果与垂直混合土壤的长达1.5 mA的延长表面住宅一致，厚度为3米。我们得出结论，在近近表面停留时间累积的BE-10浓度累积在近近表面次数期间的浓度可能会导致在COH中低估单核素（BE-10）宽的剥落速率。此外，如果假设从表面产生的预埋地Al-26 / BE-10比率，则可以高估由砂尺石英晶粒融合的穴位沉积物样品的埋藏年龄。 （c）2019 John Wiley＆Sons，Ltd。

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