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Active tectonics, landscape evolution and sediment dynamics in Dehra Dun, Northwest Himalaya inferred from geomorphic indices and GIS tools
Quaternary International ( IF 2.2 ) Pub Date : 2020-12-30 , DOI: 10.1016/j.quaint.2020.12.040
Swati Sinha , Rajiv Sinha

Geomorphic evolution of the frontal parts of active mountain belts is strongly influenced by tectonic processes, usually manifested in fluvial, structural and morphotectonic parameters of the landscape. Geomorphic indices have long been used for understanding the tectonic imprints in river basins. However, their applicability and validation from field observations in the Himalayan basins have often been debated. Here we test the applicability of several geomorphic indices in the western Dehra Dun (intermontane valley) that includes well-known tectonic elements such as Main Boundary thrust (MBT), Main Frontal Thrust (MFT), Santaurgarh Thrust (ST), and other smaller faults. Based on the spatial distribution of the values of different geomorphic indices, we map four different tectonic zones to represent the relative tectonic activity from low to very high. We conclude from morphometric analysis that the MBT and the ST are active faults. However, we do not find any geomorphic evidence of recent activity along several other faults mapped in this region or any deformation in the major fan units. We argue that active tectonics has not played a significant role in shaping the landforms in this region except for providing accommodation space and sediment supply for the deposition of fan units. We have further employed DEM and limited borehole data to understand the sediment storage and excavation at Holocene time scale. We compute the average stored volume of sediments since ∼50 ka as 8.03 × 1010 m3 (using borehole data) and 12.24 × 1010 m3 (GIS approach). Total eroded volume has been computed as 0.47 × 1010 m3 (using borehole data) and 0.64 × 1010 m3 (GIS approach). These volumes give a time-averaged sediment discharge leaving the dun as 0.21–0.39 × 106 m3/yr over Late Quaternary period. We note that the estimated average eroded material during the incision phase is only 5–6% of the total accumulated sediment volume. Further, the average estimated volume (8.03–12.24 × 1010 m3) in the valley is nearly half of the volume of the sediment that can be accommodated (27.2 × 1010 m3) in the valley. Also, the present-day sediment supply to the Dun (∼0.14 × 106 m3/yr) is low in comparison to estimated average erosion rate. Our results therefore suggest that the valley is only half filled, and is in excavation phase since Late Quaternary mostly driven by climatic perturbations.



中文翻译:

从地貌指数和GIS工具推断喜马拉雅西北部德拉敦的活跃构造,景观演化和沉积动力学

活动山带锋面部分的地貌演化受构造过程的强烈影响,通常表现在景观的河流,结构和构造构造参数中。长期以来,地貌指数一直用于了解流域的构造印记。然而,它们在喜马拉雅盆地实地观测中的适用性和有效性经常被争论。在这里,我们测试了Dehra Dun(西部山间山谷)西部几个地貌指数的适用性,其中包括著名的构造元素,例如主边界逆冲(MBT),主额顶冲(MFT),Santaurgarh冲断(ST)以及其他较小的故障。根据不同地貌指数值的空间分布,我们绘制了四个不同的构造带,以表示从低到高的相对构造活动。我们从形态分析得出结论,MBT和ST是活动断层。但是,我们没有发现沿该区域测绘的其他几个断层的近期活动的地貌证据或主要扇形单元的任何变形。我们认为,活跃的构造学在为该地区的地貌塑造过程中没有发挥重要作用,除了为风扇单元的沉积提供容纳空间和沉积物供应外。我们进一步采用了DEM和有限的钻孔数据,以了解全新世时标的沉积物存储和挖掘。我们计算了约50 ka以来沉积物的平均存储量为8.03×10 我们没有发现沿该区域测绘的其他几个断层的近期活动的地貌证据或主要扇形单元的任何变形。我们认为,活跃的构造学在为该地区的地貌塑造过程中没有发挥重要作用,除了为风扇单元的沉积提供容纳空间和沉积物供应外。我们进一步采用了DEM和有限的钻孔数据,以了解全新世时标的沉积物存储和挖掘。我们计算了约50 ka以来沉积物的平均存储量为8.03×10 我们没有发现沿该区域测绘的其他几个断层的近期活动的地貌证据或主要扇形单元的任何变形。我们认为,活跃的构造学在为该地区的地貌塑造过程中没有发挥重要作用,除了为风扇单元的沉积提供容纳空间和沉积物供应外。我们进一步采用了DEM和有限的钻孔数据,以了解全新世时标的沉积物存储和挖掘。我们计算了约50 ka以来沉积物的平均存储量为8.03×10 我们认为,活跃的构造学在为该地区的地貌塑造过程中没有发挥重要作用,除了为风扇单元的沉积提供容纳空间和沉积物供应外。我们进一步采用了DEM和有限的钻孔数据,以了解全新世时标的沉积物存储和挖掘。我们计算了约50 ka以来沉积物的平均存储量为8.03×10 我们认为,活跃的构造学在为该地区的地貌塑造过程中没有发挥重要作用,除了为风扇单元的沉积提供容纳空间和沉积物供应外。我们进一步采用了DEM和有限的钻孔数据,以了解全新世时标的沉积物存储和挖掘。我们计算了约50 ka以来沉积物的平均存储量为8.03×1010  m 3(使用井眼数据)和12.24×10 10  m 3(GIS方法)。总侵蚀量已计算为0.47×10 10  m 3(使用井眼数据)和0.64×10 10  m 3(GIS方法)。这些体积给出了平均时间的沉积物排泄量,在第四纪后期,沙丘留出量为0.21-0.39×10 6  m 3 /年。我们注意到,切口阶段估计的平均侵蚀材料仅为总沉积物体积的5–6%。此外,平均估算体积(8.03–12.24×10 10  m 3)中的)几乎是谷中可容纳的沉积物体积的一半(27.2×10 10  m 3)。此外,与估计的平均侵蚀率相比,目前向邓恩提供的沉积物数量少(约0.14×10 6  m 3 / yr)。因此,我们的结果表明,该山谷仅被填满了一半,并且处于开挖阶段,因为第四纪晚期主要是由气候扰动驱动的。

更新日期:2020-12-30
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