The cosmogenic record of mountain erosion transmitted across a foreland basin: Source-to-sink analysis of in situ 10Be, 26Al and 21Ne in sediment of the Po river catchment
The cosmogenic record of mountain erosion transmitted across a foreland basin: Source-to-sink analysis of in situ 10Be, 26Al and 21Ne in sediment of the Po river catchment
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DOI：
10.1016/j.epsl.2016.07.017
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发表时间：
2016-10
影响因子：
5.3
通讯作者：
H. Wittmann;M. Malusà;A. Resentini;E. Garzanti;S. Niedermann
中科院分区：
文献类型：
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作者：
H. Wittmann;M. Malusà;A. Resentini;E. Garzanti;S. Niedermann
我们分析了来自阿尔卑斯、亚平宁、洪泛区和三角洲的Po河流域现代沉积物中10 Be、26 Al和21 Ne的原位浓度从源到汇的变化，以研究造山侵蚀的宇宙成因记录如何在快速沉降的前陆盆地中传播。分析样品中的原位10 Be浓度范围为~ 0.8× 10.4 at/g QTZ至~ 6.5× 10.4 at/g QTZ。10个be推算的剥蚀速率在高寒源区为0.1 ~ 1.5 mm/yr，在亚平宁源区为0.3 ~ 0.5 mm/yr。在阿尔卑斯中部西部发现了最高的10个贝氏衍生剥蚀率（1.5 mm/年）。根据这些数据，我们限制了离开阿尔卑斯和亚平宁源区的沉积物通量（分别为27mt /年和50mt /年），这明显高于测量提供的沉积物输出估计值（在波河三角洲为10mt /年）。我们观察到来源地区的10种Be浓度和10种Be衍生的剥蚀率具有很高的变异性。同时，阿尔卑斯山脉和亚平宁山脉的面积加权10 - Be浓度（2.29±1.57）× 10 - 4 at/g QTZ（数据集的±1 SD）在Po平原沉积物中（（2.68±0.78，±1 SD）× 10 - 4 at/g QTZ）的修正程度较差（受支流输入）。波河漫滩的缓冲作用在很大程度上消除了10be信号的散射。我们测试了在Po盆地源到汇转移过程中宇宙核素记录的几个潜在扰动。我们发现沉积物被困在深冰湖或水坝后面，对10倍山记录没有显著的改变。例如，在冰川后的马焦雷湖的上游和下游测量了相似的10 - Be浓度，这表明湖泊形成之前的剥蚀率与今天相似。在全流域尺度上，有大坝流域与无大坝流域的10 Be浓度基本一致。由于测量到的26 Al/10 be比值没有显示出深埋物质的添加，因此可以排除在沉降的Po平原沉积物储存期间10 be山记录的潜在修改。波河平原几乎无法分辨的过量21 Ne信号表明，在河漫滩地表移动过程中，以前被侵蚀的沉积物进行了再循环，而不是宇宙成因核素的积累。我们的研究结果表明，山脉侵蚀的宇宙成因记录可以有效地从源区传递到沉积汇，甚至跨越强烈沉降的前陆盆地。我们发现，这一记录很少受到一系列潜在的地质和人为偏差源的影响，并且在很大程度上与上游沉积物拦截和洪泛区沉积物储存无关。
We analyze the source-to-sink variations of in situ 10 Be, 26 Al and 21 Ne concentrations in modern sediment of the Po river catchment, from Alpine, Apennine, floodplain, and delta samples, in order to investigate how the cosmogenic record of orogenic erosion is transmitted across a fast-subsiding foreland basin. The in situ 10 Be concentrations in the analyzed samples range from∼ 0.8× 10 4 at/g QTZ to∼ 6.5× 10 4 at/g QTZ. The 10 Be-derived denudation rates range from 0.1 to 1.5 mm/yr in the Alpine source areas and from 0.3 to 0.5 mm/yr in the Apenninic source areas. The highest 10 Be-derived denudation rates are found in the western Central Alps (1.5 mm/yr). From these data, we constrain a sediment flux leaving the Alpine and the Apenninic source areas (> 27 Mt/yr and ca. 5 Mt/yr, respectively) that is notably higher than the estimates of sediment export provided by gauging (∼ 10 Mt/yr at the Po delta). We observe a high variability in 10 Be concentrations and 10 Be-derived denudation rates in the source areas. In the Po Plain, little variability is observed, and at the same time, the area-weighed 10 Be concentration of (2.29±1.57)× 10 4 at/g QTZ (±1 SD of the dataset) from both the Alps and the Apennines is poorly modified (by tributary input) in sediment of the Po Plain ((2.68±0.78,±1 SD)× 10 4 at/g QTZ). The buffering effect of the Po floodplain largely removes scatter in 10 Be signals. We test for several potential perturbations of the cosmogenic nuclide record during source to sink transfer in the Po basin. We find that sediment trapping in deep glacial lakes or behind dams does not significantly change the 10 Be-mountain record. For example, similar 10 Be concentrations are measured upstream and downstream of the postglacial Lake Maggiore, suggesting that denudation rates prior to lake formation were similar to today's. On the scale of the entire basin, the 10 Be concentration of basins with major dams is similar to those without major dams. A potential modification of the 10 Be-mountain record during sediment storage in the subsiding Po Plain can be excluded as measured 26 Al/10 Be ratios do not show the addition of deeply buried material. A barely resolvable excess 21 Ne signal in the Po plain indicates recycling of previously eroded sediment rather than accumulation of cosmogenic nuclides during surficial floodplain transport. Our results demonstrate that the cosmogenic record of mountain erosion is effectively transmitted from the source areas to the sediment sink, even across a strongly subsiding foreland basin. We show that this record is poorly influenced by a range of potential geological and anthropogenic sources of bias, and is largely independent from upstream sediment interception and sediment storage in the floodplain.