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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >The distribution of sediment residence times at the foot of mountains and its implications for proxies recorded in sedimentary basins
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The distribution of sediment residence times at the foot of mountains and its implications for proxies recorded in sedimentary basins

机译：山脚下沉积物停留时间的分布及其对沉积盆中录制代理的影响

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The geochemical and physical properties of terrigenous sediment stacked in sedimentary basins are used as proxies for the paleo-environmental conditions that prevailed during their period of deposition. Nevertheless, sediment grains have a stochastic transit from mountain sources to sedimentary basins: a fraction of grains are stored for a long time while others are recycled from old deposits. Consequently, the temporal representativity of a population of grains in a sedimentary stratum is uncertain. The potential recycling of old material is a major concern in the reconstruction of paleo-environments and this recycling is usually difficult to evaluate. In particular, the distribution of grain residence times in basins, between sources and sinks, is out of reach. Here we use a landscape evolution model that traces grains to analyse the distribution of residence times in an alluvial apron at the foot of a mountain relief. We study an end-member scenario that is the least favourable for the storage of grains: when the mountain is eroding at the same rate as rock is uplifting. In this case, the alluvial apron behaves as a by-pass zone, when averaging sediment flux over Ma, and the storage of grains of any size should be minimal. Yet, the model predicts that some grains are stored for hundreds of thousands of years before exiting the alluvial apron. Consequently, the mean residence time of sediment grains is much higher than the observed residence time of 95% of the grains exported by the alluvial apron rivers. This process may explain very long residence times found in fluvial systems by geochemical methods based on bulk measurements of sediment. Furthermore, it suggests that grains stored for a very long time, although a minority, can bias time-dependent proxies.(C) 2020 Elsevier B.V. All rights reserved.
机译：沉积盆地中堆积的土井沉积物的地球化学和物理性质用作古环境条件的代理，其沉积期间普遍存在。尽管如此，沉积物谷物从山来源到沉积盆地的随机交通：一部分晶粒储存了很长时间，而其他颗粒从旧矿床中回收。因此，沉积层中粒群的时间表示不确定。旧材料的潜在回收是重建古环境的主要问题，并且这种回收通常难以评估。特别是，盆地在盆地之间的谷物停留时间分布在源和水槽之间是不可触及的。在这里，我们使用横向演化模型，追踪谷物，分析山脉脚脚下的冲积围裙中的停留时间分布。我们研究了最终成员的情景，这是最不利的谷物的储存：当山上以与岩石相同的速度侵蚀时。在这种情况下，当平均沉积物通量超过MA时，冲积的围绕表现为旁路区，并且任何尺寸的谷物的存储应该是最小的。然而，该模型预测，在离开冲积围裙之前，一些谷物储存数十万年。因此，沉积物晶粒的平均停留时间远高于被冲积围裙河流出口出口的95％的颗粒的观察到时间。该过程可以通过基于沉积物的散装测量来解释河流系统中发现的非常长的住宿时间。此外，它表明，虽然少数群体，但虽然少数群体，但仍然可以偏离时间依赖的代理。（c）2020 elsevier b.v.保留所有权利。

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