Geometry and grain-size characteristics of the basal surface of a braided river deposit
Geometry and grain-size characteristics of the basal surface of a braided river deposit
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辫状河沉积物底面的几何形状和粒度特征
DOI：
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发表时间：
2011
期刊：
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通讯作者：
Peter E. Ashmore
中科院分区：
文献类型：
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作者：
J. Tobias Gardner;Peter E. Ashmore
描述河流沉积物的三维几何形状和粒度模式及其与河流形态动力学的关系一直是沉积学中难以实现的目标，但受到有限的暴露和河流动力学的时间尺度的阻碍。在小规模物理模型中，时间尺度足够短，可以绘制河流及其沉积物显着（且连续）形态发展过程中的河流形态和沉积学，特别是辫状河。使用近距离数字摄影测量，利用数字高程模型差分技术，结合图像纹理分析的自动粒度映射，捕获河流形态的动态以及由此产生的沉积几何和沉积学。利用这些新颖的方法，我们展示了辫状河沉积物几何形状的时间发展和特征，并首次绘制了辫状河沉积物基底表面的特征和发育与河流形态动力学和形成过程的关系。底面具有相当大的起伏，颗粒尺寸的变化与河流整体相似，随着时间的推移，通过河道的转换而逐渐发展，产生相邻的不同年龄的底面切口斑块和带子，并且仅部分与横向迁移河道汇合相关的河床冲刷有关。
Description of the three-dimensional geometry and grain-size patterns of fluvial deposits and their relationship to the morphodynamics of the river has been an elusive objective in sedimentology, hindered by limited exposure and the time scale of fluvial dynamics. In small-scale physical models the time scales are short enough to map river morphology and sedimentology during significant (and continuous) morphological development of the river and its deposits, especially for braided rivers. Using close-range digital photogrammetry, the dynamics of the river morphology, and resulting deposit geometry and sedimentology, were captured using digital elevation model differencing techniques, combined with automated grain-size mapping from image texture analysis. Using these novel methods we show the temporal development and characteristics of braided river deposit geometry, and, for the first time, map the characteristics and development of the basal surface of braided river deposits in relation to river morphodynamics and formative processes. The basal surface has considerable relief, wide variation in grain size similar to that of the river as a whole, develops progressively over time by switching of channels producing adjacent patches and ribbons of basal incision of different ages, and is only partially related to bed scour associated with laterally migrating channel confluences.