How to recognize crescentic bedforms formed by supercritical turbidity currents in the geologic record: Insights from active submarine channels
How to recognize crescentic bedforms formed by supercritical turbidity currents in the geologic record: Insights from active submarine channels
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DOI：
10.1130/g40095.1
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发表时间：
2018-06-01
期刊：
影响因子：
5.8
通讯作者：
Vellinga, Age J.
中科院分区：
文献类型：
--
作者：
Hage, Sophie;Cartigny, Matthieu J. B.;Vellinga, Age J.
在整个地质时期，海底通道一直是重要的，它将全球大量的沉积物从陆地输送到深海。现代观测表明，超临界浊流（海底沉积物流）可以塑造海底通道，从而产生具有新月形平面形态的上游迁移底形。为了准确地解释地质记录中的超临界流动和沉积环境，重要的是能够识别新月形底形的沉积特征。野外地质学家通常将含有大量砂的冲刷充填物与新月形底形联系起来，而浊流模型产生的沉积物主要由后退床组成。在这里，我们调和这一明显的矛盾，提出了最详细的研究，结合直接流动观测，延时海底测绘和沉积物岩心，从而提供了从流动过程中的链接沉积产品。这些数据是在加拿大斯夸米什米什三角洲海底通道的近端部分收集的。我们证明，床型迁移最初产生后退床的砂。然而，这些后退床在随后的流动过程中被进一步的床形迁移部分侵蚀，导致含有大量沙子的冲刷填充。因此，我们的观测结果更好地匹配河流模型产生的上游迁移床型的沉积结构，尽管事实上，它们是在浊流下形成的。
Submarine channels have been important throughout geologic time for feeding globally significant volumes of sediment from land to the deep sea. Modern observations show that submarine channels can be sculpted by supercritical turbidity currents (seafloor sediment flows) that can generate upstream-migrating bedforms with a crescentic planform. In order to accurately interpret supercritical flows and depositional environments in the geologic record, it is important to be able to recognize the depositional signature of crescentic bedforms. Field geologists commonly link scour fills containing massive sands to crescentic bedforms, whereas models of turbidity currents produce deposits dominated by back-stepping beds. Here we reconcile this apparent contradiction by presenting the most detailed study yet that combines direct flow observations, time-lapse seabed mapping, and sediment cores, thus providing the link from flow process to depositional product. These data were collected within the proximal part of a submarine channel on the Squamish Delta, Canada. We demonstrate that bedform migration initially produces back-stepping beds of sand. However, these back-stepping beds are partially eroded by further bedform migration during subsequent flows, resulting in scour fills containing massive sand. As a result, our observations better match the depositional architecture of upstream-migrating bedforms produced by fluvial models, despite the fact that they formed beneath turbidity currents.