Alluvial architecture of mid-channel fluvial-tidal barforms: The mesotidal Lower Columbia River, Oregon/Washington, USA
Alluvial architecture of mid-channel fluvial-tidal barforms: The mesotidal Lower Columbia River, Oregon/Washington, USA
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河道中部河流潮汐坝形的冲积建筑：美国俄勒冈州/华盛顿州哥伦比亚河下游中潮汐区
DOI：
10.1111/sed.12754
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发表时间：
2020
期刊：
影响因子：
3.5
通讯作者：
Prokocki E
中科院分区：
文献类型：
--
作者：
Prokocki E
中潮到大潮河流-潮汐转换的条形体，无论河流流量如何，目前认为显示出由潮汐特征主导的沉积结构。由于现代中潮河流-潮汐转换的观测资料很少，特别是那些多河道的大型河流（年平均流量≥7000 m3 s − 1，峰值流量≥ 15000 m3 s −1）和河道中间的沙洲，这个概念仍然没有得到证实。本研究分析了由高分辨率探地雷达和耦合浅层振动孔（深度<5 m）组合产生的数据，这些数据采集自美国华盛顿/俄勒冈州中潮多沟道下哥伦比亚河的现代河流-潮汐中沟沙洲，其峰值流量≥18 000 m3 s −1。这些数据与时间序列航空影像一起使用，以表征这些沙洲在单一流或由河流，潮汐和/或风浪振荡组成的组合流中的时空沉积学演变，当前组件在独特的河流-潮汐过渡制度中运行。结果表明，约75%的下哥伦比亚河河流-潮汐过渡区产生了辫状坝，其底部至坝顶沉积学结构与文献中记录的仅河流辫状坝无法区分。因此，中潮大型河流的河流-潮汐转换内的条形地层特征更可能由下游方向的水流主导。此外，在上混合潮汐-河流体系辫状坝内的坝顶加积组中发现了一种新的低角度（<5°）倾斜异石层结。这种常见的分层是由以流域内风浪振荡流和双向潮流为特征的混合流产生的。这种倾斜的杂岩分层标志着从下哥伦比亚河上倾完全河流辫状坝结构到那些具有坝顶相的初始下游河流-潮汐交叉点，坝顶相是由流域内风浪和潮汐影响的水力沉积反应产生的。当保存下来时，这种形式的中间河道砂坝倾斜的杂岩分层提供了一个独特的多通道河流-潮汐过渡的沉积学特征，该过渡具有一个具有盆内风浪的开放水域较低盆地。
Barforms of mesotidal to macrotidal fluvial–tidal transitions, regardless of fluvial‐discharge, are currently thought to display a sedimentary architecture dominated by tidal signatures. Due to the scarcity of observations from modern mesotidal fluvial–tidal transitions, especially those of multi‐channelled large‐rivers (mean annual discharge ≥7000 m3s−1and peak discharges ≥15 000 m3s−1) with mid‐channel bars, this concept remains unproven. The present study analyses data produced by a combination of high‐resolution ground penetrating radar and coupled shallow vibracores (<5 m depth), collected from modern fluvial–tidal mid‐channel bars of the mesotidal multi‐channelled Lower Columbia River, Washington/Oregon, USA, which can experience peak discharges ≥18 000 m3s−1. These data were used alongside time‐sequenced aerial imagery to characterize the spatio‐temporal sedimentological evolution of these barforms in singular flows or combined flows consisting of river, tidal and/or wind‐wave oscillatory, current components operating in unique fluvial–tidal transition regimes. Results indicate thatca75% of the Lower Columbia River fluvial–tidal transition produces braid‐bars with basal to bar‐top sedimentological architectures that are indistinguishable from fluvial‐only braid‐bars recorded in the literature. Barform stratal characteristics within the fluvial–tidal transitions of mesotidal large‐rivers are therefore more likely to be dominated by downstream‐oriented currents. Furthermore, a new style of low‐angle (<5°) inclined heterolithic stratification found in bar‐top accretion‐sets within upper‐mixed tidal–fluvial regime braid‐bars is observed. This common stratification is created by combined‐flows characterized by intrabasinal wind‐wave oscillatory‐currents and bidirectional tidal‐currents. This inclined heterolithic stratification marks the initial downstream fluvial–tidal crossover point from Lower Columbia River up‐dip fully‐fluvial braid‐bar architectures, to those possessing bar‐top facies produced by the hydraulic‐sedimentation response of combined intrabasinal wind‐wave and tidal influence. When preserved, this form of mid‐channel bar inclined heterolithic stratification provides a unique sedimentological signature of multi‐channelled fluvial–tidal transitions that possess an open‐water lower basin with intrabasinal wind‐waves.