Landscape response to late Pleistocene climate change in NW Argentina: Sediment flux modulated by basin geometry and connectivity
Landscape response to late Pleistocene climate change in NW Argentina: Sediment flux modulated by basin geometry and connectivity
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DOI：
10.1002/2015jf003607
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发表时间：
2016-02
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通讯作者：
T. Schildgen;R. Robinson;S. Savi;W. Phillips;J. Spencer;B. Bookhagen;D. Scherler;Stefanie Tofelde;R. Alonso;P. Kubik;S. Binnie;M. Strecker
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作者：
T. Schildgen;R. Robinson;S. Savi;W. Phillips;J. Spencer;B. Bookhagen;D. Scherler;Stefanie Tofelde;R. Alonso;P. Kubik;S. Binnie;M. Strecker
河流充填阶地保存了景观对气候变化反应的沉积档案，通常超过千年的时间尺度。在阿根廷西北部的Humahuaca盆地（东部科迪勒拉，南部中央安第斯山脉），我们的29个新的光激发光年龄晚更新世填充阶地沉积物表明，过去的河流加积的时间发生在不同的时间间隔上的西部和东部的山谷，尽管他们相似的基岩岩性，平均坡度和降水。在西部，淤积与降水增加的时期相吻合，而在东部，淤积与降水减少或更多的可变条件相吻合。侵蚀速率和粒度的依赖性，在我们的宇宙成因10Be现代和填充阶地沉积物的分析揭示了一个增加的重要性相比，今天在西边的加积过程中的滑坡，但同样的重要性在东边加积。沉积的时间和10Be数据的差异可能是由于在山谷的几何形状，这导致沉积物暂时存储在栖息盆地的东侧的差异。似乎降水量增加的时期引发了整个地区的山体滑坡，导致西部的淤积，但东部栖息盆地下游狭窄的基岩峡谷被堵塞。因此，盆地的几何形状和河流的连通性似乎强烈影响沉积物运动通过系统的时间。对于整合了具有不同几何形状或连通程度的次盆地的较大盆地（如Humahuaca），沉积对气候强迫的响应可能会减弱。
Fluvial fill terraces preserve sedimentary archives of landscape responses to climate change, typically over millennial timescales. In the Humahuaca Basin of NW Argentina (Eastern Cordillera, southern Central Andes), our 29 new optically stimulated luminescence ages of late Pleistocene fill terrace sediments demonstrate that the timing of past river aggradation occurred over different intervals on the western and eastern sides of the valley, despite their similar bedrock lithology, mean slopes, and precipitation. In the west, aggradation coincided with periods of increasing precipitation, while in the east, aggradation coincided with decreasing precipitation or more variable conditions. Erosion rates and grain size dependencies in our cosmogenic 10Be analyses of modern and fill terrace sediments reveal an increased importance of landsliding compared to today on the west side during aggradation, but of similar importance during aggradation on the east side. Differences in the timing of aggradation and the 10Be data likely result from differences in valley geometry, which causes sediment to be temporarily stored in perched basins on the east side. It appears as if periods of increasing precipitation triggered landslides throughout the region, which induced aggradation in the west, but blockage of the narrow bedrock gorges downstream from the perched basins in the east. As such, basin geometry and fluvial connectivity appear to strongly influence the timing of sediment movement through the system. For larger basins that integrate subbasins with differing geometries or degrees of connectivity (like Humahuaca), sedimentary responses to climate forcing are likely attenuated.