The Transport History of Alluvial Fan Sediment Inferred From Multiple Geochronometers
The Transport History of Alluvial Fan Sediment Inferred From Multiple Geochronometers
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DOI：
10.1029/2021jf006096
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发表时间：
2021-08
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影响因子：
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通讯作者：
B. Goehring;N. Brown;S. Moon;K. Blisniuk
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作者：
B. Goehring;N. Brown;S. Moon;K. Blisniuk
我们提出了一种多计时器方法来细化冲积扇的年龄并推断南加州安萨博雷戈沙漠地区的沉积物运输和沉积历史。我们现场测量了扇表面巨石产生的宇宙成因碳 14 (14C) 和冲积层内单个长石颗粒的红外受激发光 (IRSL) 年龄。我们的新 IRSL 年龄 [5.3 ± 0.5 ka (±1σ)] 与现有的铀系列 [U 系列； 5.3±0.2(±2σ)]成土碳酸盐岩年龄。 IRSL 和 U 系列年龄表明，巨石的原位 14C 测量结果 [6.6 ± 1.1 ka (±1σ)] 包含来自上游流域先前暴露的继承核素，与寿命较长的核素铍-10 (10Be) 的测量结果非常相似。然而，原位 14C 年龄更接近从 IRSL 和 U 系列推断的首选年龄，并且比对比 10Be 年龄分散更少。我们的数据表明，多地质年代仪方法将以最大程度的置信度得出冲积扇表面的年龄。然后，我们应用成对的 14C 和 10Be 浓度来推断采样巨石的先前暴露和储存时间分别为 3.1 ± 3.2 和 4.6 ± 2.3 Kyr。单粒 IRSL 年龄的混合模型分析表明，在重新动员之前的双峰储存持续时间，峰值约为 100 小时。 2 和 10 基尔。我们证明宇宙成因核素遗传和单颗粒 IRSL 等效剂量分布可以提供有关沉积物沉积在冲积扇上之前的沉积物传输历史的附加信息。
We present a multi‐chronometer approach to refine the age of an alluvial fan and to infer sediment transport and deposition history in the Anza Borrego Desert region of Southern California. We measure in situ produced cosmogenic carbon‐14 (14C) from boulders on the fan surface and infrared stimulated luminescence (IRSL) ages from single feldspar grains within the alluvium. Our new IRSL age [5.3 ± 0.5 ka (±1σ)] is in excellent agreement with existing uranium‐series [U‐series; 5.3 ± 0.2 (±2σ)] ages of pedogenic carbonates. The IRSL and U‐series ages show that in situ 14C measurements [6.6 ± 1.1 ka (±1σ)] from boulders contain inherited nuclides from prior exposure in the upstream catchment, much like measurements of the longer‐lived nuclide, beryllium‐10 (10Be). However, in situ 14C ages are closer to the preferred ages inferred from IRSL and U‐series and with less scatter than comparative 10Be ages. Our data demonstrate that a multi‐geochronometer approach will produce ages of alluvial fan surfaces with the greatest degree of confidence. We then apply the paired 14C and 10Be concentrations to infer the prior exposure and storage duration of the sampled boulders of 3.1 ± 3.2 and 4.6 ± 2.3 Kyr, respectively. A mixture model analysis of the single grain IRSL ages suggests bimodal storage durations prior to remobilization with peaks at ca. 2 and 10 Kyr. We demonstrate that cosmogenic nuclide inheritance and single grain IRSL equivalent dose distributions can provide additional information regarding sediment transport history prior to deposition on the alluvial fan.