Himalayan valley-floor widths controlled by tectonically driven exhumation
Himalayan valley-floor widths controlled by tectonically driven exhumation
复制标题
DOI：
10.1038/s41561-023-01238-8
复制
发表时间：
2023-07
影响因子：
18.3
通讯作者：
F. Clubb;S. Mudd;T. Schildgen;P. A. van der Beek;R. Devrani;H. Sinclair
中科院分区：
文献类型：
--
作者：
F. Clubb;S. Mudd;T. Schildgen;P. A. van der Beek;R. Devrani;H. Sinclair
喜马拉雅河流每年将数十亿吨沉积物输送到海洋盆地。山谷是该路线系统的重要组成部分：这些山谷中的储存可以缓冲下游沉积系统记录的气候和构造信号。尽管迫切需要了解这些山谷填充物的空间分布、体积和寿命，但对山谷位置和几何形状的控制尚不清楚，沉积物体积的估计是基于山谷加宽过程的假设。在这里，我们提取了喜马拉雅山超过 150 万个谷底宽度测量值，以确定对谷底形态的主要控制因素并评估沉积物储存过程。使用随机森林回归，我们表明河道陡度（岩石隆升的代表）是对谷底宽度的一阶控制。根据 1,148 个折返率的数据集，我们发现谷底宽度随着折返率的增加而减小。我们的研究结果表明，谷底宽度是由长期构造驱动的折返控制的，而不是由水排放或基岩侵蚀性控制的，谷底加宽主要是由于沿低梯度谷底的沉积物沉积而不是横向基岩侵蚀造成的。山地系统中的谷地充当沉积物的临时汇，沉积物从山坡上的源头迁移到前陆或海洋盆地的最终安息地。这种存储可以缓冲、粉碎或破坏传播的沉积信号 1-3。因此，了解山谷沉积物填充物的空间分布、体积和寿命对于从沉积档案中重建景观演化至关重要。然而，目前对喜马拉雅山谷填土空间分布的控制尚不清楚。过去以比例 4 绘制山谷填土体积和停留时间的努力依赖于这样的假设：山谷表面下方的地形与暴露的边坡相似，因此山谷壁几乎没有发生侧向侵蚀。
Himalayan rivers transport around a gigaton of sediment annually to ocean basins. Mountain valleys are an important component of this routing system: storage in these valleys acts to buffer climatic and tectonic signals recorded by downstream sedimentary systems. Despite a critical need to understand the spatial distribution, volume and longevity of these valley fills, controls on valley location and geometry are unknown, and estimates of sediment volumes are based on assumptions of valley-widening processes. Here we extract over 1.5 million valley-floor width measurements across the Himalaya to determine the dominant controls on valley-floor morphology and to assess sediment-storage processes. Using random forest regression, we show that channel steepness, a proxy for rock uplift, is a first-order control on valley-floor width. On the basis of a dataset of 1,148 exhumation rates, we find that valley-floor width decreases as exhumation rate increases. Our results suggest that valley-floor width is controlled by long-term tectonically driven exhumation rather than by water discharge or bedrock erodibility and that valley widening predominantly results from sediment deposition along low-gradient valley floors rather than lateral bedrock erosion.Valleys in mountain systems act as transient sinks for sediments that journey from sources on mountain hillslopes to their final resting place in forelands or ocean basins. This storage can buffer, shred or destroy propagating sedimentary signals 1–3. Therefore, understanding the spatial distribution, volumes and longevity of valley sediment fills is essential to reconstruct landscape evolution from sedimentary archives. However, controls on the spatial distribution of valley fills across the Himalaya are currently unknown. Past efforts to map the volumes and residence times of valley fills at scale 4 rely on the assumption that topography underneath the valley surface is similar to that of the exposed side slopes and therefore that little lateral erosion of the valley walls has taken place.