Extremes in dune preservation: Controls on the completeness of fluvial deposits
Extremes in dune preservation: Controls on the completeness of fluvial deposits
复制标题
沙丘保存的极端情况：对河流沉积物完整性的控制
DOI：
10.1016/j.earscirev.2015.09.008
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发表时间：
2015
影响因子：
12.1
通讯作者：
Reesink A
中科院分区：
文献类型：
--
作者：
Reesink A
了解沉积保存巩固了我们解释古代沉积记录和重建古环境和古气候的能力。沙丘集是普遍存在的保存河流沉积物，通常解释的基础上，描述了在垂直序列的侵蚀复发的模型，但不考虑空间变异性。然而，水流和泥沙输运的空间变异性将改变侵蚀的复发，从而改变沙丘的保存。为了更好地理解这些解释的局限性，并概述了潜在的变化，在保存潜力的原因，本文回顾了现有的工作，并提出了新的意见的一个极端的终端成员沙丘保存：“形集”，形成的沙丘中，两个stoss和背风坡保存完好。这些形式集不符合模型的基础上反复侵蚀，因为侵蚀不复发，在他们的情况下，因此可以用来评估的假设，巩固沉积preservation.New探地雷达数据从巴拉那河，阿根廷，显示沙丘领域被完整地埋在较大规模的酒吧。这些型组序列的长度可达300 m，仅限于河道沉积物上部5 m的单元沙坝槽，出现在> 5%的河道中部沙坝沉积物中，显示出再活化面，出现在多个层次，并与平均流动沙丘的大小相匹配。对已发表的形式集的评论强调了可以设想的形成形式集的各种过程：i）极端洪水后的废弃，ii）被遮蔽的沙坝槽和曲流颈截止区中的粘性粘土缓慢掩埋废弃沙丘，iii）块体运动过程的快速掩埋，和iv）由于局部沉积作用对沙丘迁移的支配作用，沙丘群的爬升。对这些新的和已发表的有关型群及其埋藏过程的描述的分析表明，集合不需要指示极端洪水。相反，形集与周围的地貌，如河岸，曲流颈截止，酒吧，因为这种大规模的背景下控制当地的沉积物预算和侵蚀复发的性质密切相关。局部增强保存的沉积的“极端”的优势，进一步促进了更细的粒度和流动阶段的长期变化。这种情况是诸如巴拉那河等大型低地河流的特点，但并不是唯一的。沙丘保护的空间控制是至关重要的：虽然在一个点的模型充分描述了近水平套自由迁移的沙丘在均匀的流动，他们是不适合倾斜的沙丘陪集和其他情况下，多尺度的底形相互作用。深泓线与大沙坝形态不同位置之间的水流和泥沙输运的时空变化可以改变河道内沙丘的保存潜力。因此，沙丘集的厚度分布很可能被分组在较大规模的单位，反映了形成沙丘的几何形状和酒吧规模的变化，在保存潜力。这里强调的多尺度保存动态也为其他沉积体系提供了有用的比较。
Understanding sedimentary preservation underpins our ability to interpret the ancient sedimentary record and reconstruct paleoenvironments and paleoclimates. Dune sets are ubiquitous in preserved river deposits and are typically interpreted based on a model that describes the recurrence of erosion in a vertical sequence, but without considering spatial variability. However, spatial variability in flow and sediment transport will change the recurrence of erosion, and therefore dune preservation. In order to better understand the limits of these interpretations and outline the causes of potential variability in preservation potential, this paper reviews existing work and presents new observations of an extreme end-member of dune preservation: ‘form-sets’, formed by dunes in which both stoss- and lee-slopes are preserved intact. These form-sets do not conform to models that are based on the recurrence of erosion, since erosion does not recur in their case, and can therefore be used to evaluate the assumptions that underpin sedimentary preservation.New Ground Penetrating Radar data from the Río Paraná, Argentina, show dune fields that are buried intact within larger scale barforms. These trains of form-sets are up to 300 m in length, are restricted to unit-bar troughs in the upper 5 m of the channel deposits, occur in > 5% of the mid-channel bar deposits, show reactivation surfaces, occur in multiple levels, and match the size of average-flow dunes. A review of published accounts of form-sets highlights a diversity of processes that can be envisaged for their formation: i) abandonment after extreme floods, ii) slow burial of abandoned dune forms by cohesive clay in sheltered bar troughs and meander-neck cut-offs, iii) fast burial by mass-movement processes, and iv) climbing of dune sets due to local dominance of deposition over dune migration.Analysis of these new and published accounts of form-sets and their burial processes highlights that form-sets need not be indicative of extreme floods. Instead, form-sets are closely associated with surrounding geomorphology such as river banks, meander-neck cut-offs, and bars because this larger-scale context controls the local sediment budget and the nature of recurrence of erosion. Locally enhanced preservation by the ‘extreme’ dominance of deposition is further promoted by finer grain sizes and prolonged changes in flow stage. Such conditions are characteristic, although not exclusive, of large lowland rivers such as the Río Paraná. The spatial control on dune preservation is critical: although at-a-point models adequately describe near-horizontal sets of freely migrating dunes in uniform flows, they are unsuitable for inclined dune co-sets and other cases where multiple scales of bedforms interact. Spatial and temporal variations in flow and sediment transport between the thalweg and different positions on larger bar-forms can change the preservation potential of dunes within river channels. Therefore, dune set thickness distributions are likely grouped in larger-scale units that reflect both formative dune geometriesandbar-scale variations in preservation potential. The multi-scale dynamics of preservation highlighted herein also provides a useful comparison for other sedimentary systems.
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影响因子：
2
作者：
R. Arnott;B. Hand
通讯作者：
R. Arnott;B. Hand
沙丘上的悬浮沉积物输送和沉积：阿根廷巴拉那河
影响因子：
3.3
作者：
R. Kostaschuk;D. Shugar;J. Best;D. Parsons;S. Lane;R. Hardy;O. Orfeo
通讯作者：
O. Orfeo
影响因子：
3.3
作者：
R. Williams;J. Brasington;D. Vericat;D. Hicks
通讯作者：
R. Williams;J. Brasington;D. Vericat;D. Hicks
影响因子：
3.5
作者：
P. Carling
通讯作者：
P. Carling
影响因子：
3.5
作者：
G. S. Sambrook Smith;J. Best;Jessica Z. LeRoy;O. Orfeo
通讯作者：
G. S. Sambrook Smith;J. Best;Jessica Z. LeRoy;O. Orfeo