Interpretation of cross strata formed by unit bars
Interpretation of cross strata formed by unit bars
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单元棒形成的交叉地层的解释
DOI：
10.1002/9781119424437.ch7
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
A. Reesink
中科院分区：
文献类型：
--
作者：
A. Reesink
这项研究说明了如何简单，系统地测量由单元坝形成的交叉地层可以揭示有关形成河流环境的有价值的信息。交叉地层中的粒度分选是通过两个过程产生的：到达沙洲边缘的沉积物的“预分选”和在背风坡沉积期间的“重新分选”。单元条交叉地层通常包含不同的预分选模式，这些模式在岩心、露头和高分辨率钻孔电阻率数据中很容易识别。现场研究和水槽实验表明，预分选模式的测量可用于量化形成叠加底形的大小，并分析与洪水相关的沉积增量。这种认识还没有被应用到岩石记录中。为了填补我们理解中的这一空白，并突出进一步研究的机会，本研究系统地调查了露头中的单元坝交错地层。对控制预分选模式维度的因素进行的敏感性分析表明，只有两个控制因素占主导地位：i）描述从休止角跨地层到低角度陪集的过渡的阈值; ii）主单元棒集的保存潜力。尽管这些因素造成了不确定性，但结果表明，露头中单元坝集的预分选模式有助于解释叠加沙丘的大小。交叉地层的测量结果表明了形成洪水通过期间沙丘发育的趋势，并为分析形成水深提供了一个可行的替代。大多数单位条在多次洪水事件中持续存在。单元坝顶部通常接近满岸水深，而休止角单元坝交错地层在河道沉积的上部更为丰富。这使得单元坝交叉地层对洪水的规模和持续时间特别敏感，并允许它们记录洪水事件的短历史。这些古水力信息可用于研究洪水期间单元坝的动态演化和重建古河流系统的古水文过程。
This study illustrates how simple, systematic measurements of cross strata formed by unit‐bars can reveal valuable information about the formative fluvial environment. The grain‐size sorting in cross strata is created by two processes: ‘pre‐sorting’ of the sediment arriving at the edge of the bar and ‘re‐sorting’ during deposition on the lee slope. Unit‐bar cross strata commonly contain distinct pre‐sorting patterns that are identified easily in cores, outcrops and high‐resolution borehole resistivity data. Field studies and flume experiments have shown that measurements of pre‐sorting patterns can be used to quantify the sizes of formative superimposed bedforms and analyse depositional increments associated with floods. This understanding has not yet been applied to the rock record. In order to fill this gap in our understanding and highlight opportunities for further research, this study systematically investigates unit‐bar cross strata in outcrops. A sensitivity analysis of factors that control the dimensions of pre‐sorting patterns indicates the dominance of only two controlling factors: i) the threshold that describes the transition from angle‐of‐repose cross strata to low‐angle co‐sets; and ii) the preservation potential of the host unit‐bar sets. Despite the uncertainty created by these factors, the results show that pre‐sorting patterns in unit‐bar sets in outcrops lend themselves to interpretation of the sizes of superimposed dunes. The measurements of the cross strata indicate trends in dune development during the passage of formative floods and provide a viable proxy for the analysis of formative water depths. Most unit bars persist over multiple flood events. Unit‐bar tops commonly approach bank‐full water depths and angle‐of‐repose unit‐bar cross strata are more abundant in the upper parts of channel deposits. This makes unit bar cross strata particularly sensitive to the magnitude and duration of floods and allows them to record short histories of flood events. This palaeo‐hydraulic information may be used to investigate the dynamic evolution of unit bars during floods and to reconstruct palaeo‐hydrographs for ancient river systems.
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影响因子：
5.8
作者：
A. Nicholas;Greg . Smith;M. Amsler;P. Ashworth;J. Best;R. Hardy;S. Lane;O. Orfeo;D. Parsons;A. Reesink;S. Sandbach;C. Simpson;R. Szupiany
通讯作者：
A. Nicholas;Greg . Smith;M. Amsler;P. Ashworth;J. Best;R. Hardy;S. Lane;O. Orfeo;D. Parsons;A. Reesink;S. Sandbach;C. Simpson;R. Szupiany
影响因子：
3.3
作者：
Nicholas A
通讯作者：
Nicholas A
沙丘保存的极端情况：对河流沉积物完整性的控制
影响因子：
12.1
作者：
Reesink A
通讯作者：
Reesink A
影响因子：
--
作者：
S. Lane;D. Parsons;J. Best;O. Orfeo;R. Kostaschuk;R. Hardy
通讯作者：
S. Lane;D. Parsons;J. Best;O. Orfeo;R. Kostaschuk;R. Hardy