3-D architecture, depositional patterns and climate triggered sediment fluxes of an alpine alluvial fan (Samedan, Switzerland)
3-D architecture, depositional patterns and climate triggered sediment fluxes of an alpine alluvial fan (Samedan, Switzerland)
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DOI：
10.1016/j.geomorph.2009.09.001
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发表时间：
2010-03
期刊：
影响因子：
3.9
通讯作者：
J. Hornung;D. Pflanz;A. Hechler;A. Beer;M. Hinderer;M. Maisch;U. Bieg
中科院分区：
文献类型：
--
作者：
J. Hornung;D. Pflanz;A. Hechler;A. Beer;M. Hinderer;M. Maisch;U. Bieg
利用9km、10m深度的地质雷达剖面，对瑞士萨梅丹附近一个面积为30万m2的高山冲积扇的沉积结构进行了三维研究。雷达相模式可以很好地校准沉积学和过时的层位，由于在扇脚的300米长的露头部分。六个主要的反射体已被确定，并代表一阶，扇宽古表面。它们由厚度达20cm的细粒沉积物组成，部分具有原始成土构造和木材遗骸，其年龄在5670±60和7515±65 a14C BP之间。在这些表面之间，可以识别出不同的沉积叶和特定的建筑元素，如通道、堤坝或泥石流口。所有这些数据都进行了地理参考，以建立一个完整的定量三维时间地层框架。这使我们能够计算过时古表面之间不同时间切片的沉积物体积和沉积物通量。沉积物通量在全新世表现出整体下降，我们解释为在集水区的沉积物生产下降的一个功能的准冰循环。自中大西洋期以来，扇的加积几乎停止，气候扰动不再反映在沉积记录中。在加积期，不同的高峰高沉积物通量可以与已知的瑞士阿尔卑斯山，这表明该系统对气候变化的高度敏感性冰川退缩的时期。我们的研究结果提供了有价值的新的见解阈值的活动和静止的高山流域扇系统及其阶段的过程中的一个准冰旋回。虽然这类数据集对于了解全球变暖情景下的动态系统和地理风险评估非常重要，但却很少有。
The sedimentary architecture of an alpine alluvial fan with a surface of 300,000m2near Samedan, Switzerland, was three-dimensionally investigated using 9km of ground penetrating radar sections with a penetration depth of 10m. Radar facies patterns could be very well calibrated to sedimentology and dated horizons due to a 300m long outcrop section at the foot of the fan. Six major reflectors have been identified and represent first order, fan-wide palaeosurfaces. They are made up of up to 20cm thick fine-grained deposits partly with initial pedogenetic structures and wood remains which yielded ages between 5670±60 and 7515±65 a14C BP. Between these surfaces different depositional lobes and specific architectural elements like channels, levees or snouts of debris flows could be identified. All these data were geo-referenced to establish a complete quantitative 3-D time-stratigraphic framework. This allowed us to calculate deposited sediment volumes and sediment fluxes for different time slices between the dated palaeosurfaces. Sediment fluxes show an overall decline during the Holocene which we interpret as the decling sediment production in the catchment area—a function of the paraglacial cycle. Since the middle Atlantic period, the aggradation of the fan almost ceased and climate perturbations are no longer reflected in the sedimentary record since then. Within the aggradation period, distinct peaks of high sediment fluxes could be correlated with known periods of glacier retreats in the Swiss Alps, which points to a high sensitivity of the system to climate changes. The results of our study give valuable new insights into thresholds of activity and quiescence of an alpine catchment-fan system and its stage in the course of a paraglacial cycle. Although very important for the understanding of such dynamic systems under global warming scenarios and geo-risk assessment, such data sets are rarely available.