Morphology, sedimentology and palaeohydraulic significance of large gravel dunes, Altai Mountains, Siberia
Morphology, sedimentology and palaeohydraulic significance of large gravel dunes, Altai Mountains, Siberia
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DOI：
10.1111/j.1365-3091.1996.tb02184.x
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发表时间：
2009-10
期刊：
影响因子：
3.5
通讯作者：
P. Carling
中科院分区：
文献类型：
--
作者：
P. Carling
更新世冰川溃决洪水形成的粗砾石床被认为是水下沙丘。这些“化石”结构与现代沙丘的形态比较表明，二维（2-D）的横向沙丘和3-D的尖形和新月形沙丘的粗砾石开发的形式与沙丘形态在较小规模的地球物理流。最陡的砾石沙丘与沙中平衡沙丘的相似性表明，粒度不是限制初级沙丘形态的主要因素。内部结构表明，二维沙丘上的流动是相对均匀的，但在三维底形流动是局部变化的。流动分离和复杂的流动发生在最陡峭的3-D沙丘。交错层很薄，很少接近休止角;因此，大多数沙丘并没有主要通过雪崩迁移，而是通过在波峰上滚动并沉积在背风坡上的夹带沙砾迁移。当洪水力量减弱时，形成了背风面。由于背风坡交错层比背风坡坡度陡，在沙丘下降阶段，沙丘被轻微削平。然而，富含淤泥的帽表明，任何高度降低是当代的最终沉积的foreset。洪水后的改造已经可以忽略不计，虽然现代地形是由沙丘槽内的黄土沉积物。背风面沉积物通常比逆坡沉积物更细，这表明
Coarse-gravel bedforms which resulted from Pleistocene glacial outburst floods are identified as subaqueous dunes. Comparison of the morphology of these ‘fossil’ structures with modern dunes shows that the form of two-dimensional (2-D) transverse dunes and 3-D cuspate and lunate dunes developed in coarse gravels is comparable with sand-dune morphology within lesser-scale geophysical flows. The similarity of the steepest gravel dunes with equilibrium dunes in sand indicates that grain size is not a major factor in constraining primary duneform. Internal structure indicates that flow over 2-D dunes was relatively uniform but over 3-D bedforms flow was locally variable. Flow separation and complex streaming of flow occurred over the steepest 3-D dunes. Cross-beds are thin and few approach the angle of repose; consequently most dunes did not migrate primarily by avalanching but by stoss-entrained gravel transported over the crests rolling-down and depositing on the lee slopes. the lee formed when flood power was waning. Some dunes were sIightly planed-down during falling stage because lee-side cross-beds tend to be steeper than the angle of the preserved lee slope. However, silt-rich caps indicate that any height reduction was contemporary with the final deposition of foresets. Post-flood modification has been negligible although the modern topography is subdued by loess deposits within the dune troughs. Lee-side sediments are often finer than the stoss-slope sediments, which indicates