University of Bern, Institute of Geological Sciences, Baltzerstrasse 1+3, CH-3001, Bern, Switzerland.
Sci Rep. 2018 Jan 9;8(1):183. doi: 10.1038/s41598-017-17182-8.
Large sediment fluxes from mountain belts have the potential to cause megafans to prograde into the neighbouring sedimentary basins. These mechanisms have been documented based from numerical modelling and stratigraphic records. However, little attention has been focused on inferring temporal changes in the concentrations of supplied sediment from coarse-grained deposits. Here, we extract changes of this variable in the field from a Late Oligocene, c. 4 km-thick suite of fluvial conglomerates situated in the North Alpine foreland basin, which evolved in response to the tectonic and erosional history of the Alps. We measure a decrease in channel depths from >2 m to <1 m and an increase in the largest grain sizes from <15 cm to >20 cm from the base to the top of the suite. These constraints are used to calculate an increase in fan surface slopes from <0.3° to >1.0° based on the Shields criteria for sediment entrainment. We combine slope and bulk grain size data with the Bagnold equation for sediment transport to infer higher concentrations of the supplied sediment. We use these shifts to propose a change towards faster erosion and a steeper landscape in the Alpine hinterland, driven by mantle-scale processes beneath the Alps.
来自山脉带的大量沉积物有可能使巨扇前积进入相邻的沉积盆地。这些机制已基于数值模拟和地层记录得到证实。然而，很少有人关注从粗粒沉积物推断供应沉积物浓度的时间变化。在这里，我们从北阿尔卑斯山前盆地中提取了晚渐新世、厚约 4 公里的一套河流砾岩中的这种变量的变化，这些砾岩是对阿尔卑斯山的构造和侵蚀历史的响应而演化的。我们从这套地层的底部到顶部测量到通道深度从 >2 米减小到 <1 米，最大粒径从 <15 厘米增加到 >20 厘米。这些约束条件用于根据泥沙夹带的 Shields 准则计算扇面坡度从 <0.3°增加到 >1.0°。我们将坡度和体 grain 粒度数据与泥沙输运的 Bagnold 方程相结合，以推断供应泥沙的浓度更高。我们利用这些变化来提出阿尔卑斯山腹地侵蚀速度加快和地形更加陡峭的变化，这是由阿尔卑斯山下方的地幔尺度过程驱动的。
