Using delta channel width to estimate paleodischarge in the rock record: geometric scaling and practical sampling criteria

IF 2 4区 地球科学 Q1 GEOLOGY
O.A. Prasojo, A.E van Yperen, T.B. Hoey, A. Owen, R. Williams
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引用次数: 0

Abstract

Quantifying paleodischarge from geological field observations remains a key research challenge. Several scaling relationships between paleodischarge and channel morphology (width; depth) have been developed for rivers and river deltas. Previous paleodischarge scaling relationships were based on discharge-catchment area scaling and an empirical flow velocity estimate (e.g. Chézy, Manning formulae) multiplied by channel cross-sectional area to derive discharge. In deltas, where marine (wave, tide) energy causes bidirectional flow within distributary channels, the available paleodischarge scaling relationships are not applicable due to their unidirectional flow assumption. Here, the spatial variability of distributary channel widths from a database of 114 global modern river deltas is assessed to understand the limit of marine influence on distributary channel widths. Using 6213 distributary channel width measurements, the median channel widths of distributary channels for each delta were correlated with bankfull discharge for river-, tide- and wave-dominated deltas, the latter two including the effect of bidirectional flow. Statistically significant width-discharge scaling relationships are derived for river- and wave-dominated deltas, with no significant relationships identified for tide-dominated deltas. By reverse bootstrapping the channel widths measured from modern deltas, the minimum number of width measurements needed to apply width-discharge scaling relationships to ancient deltaic deposits is estimated as 3 and 4 for the upstream parts of river- and wave-dominated deltas, respectively, increasing to 30 in the downstream parts of river-dominated deltas. These estimates will guide sedimentological studies that often have limited numbers of distributary channel widths exposed in the rock record. To test the reliability of these alternative width-discharge scaling relationships in the rock record, paleodischarges were estimated for the well-studied Cretaceous lower Mesa Rica Sandstone Formation, USA . Comparison of these results with the more complex Chézy-derived method suggests that these new scaling relationships are accurate. Hence, it is proposed that the scaling relationships obtained from modern deltas can be applied to the rock record, requiring fewer, and easier to measure, data inputs than previously published methods.
用三角洲河道宽度估算岩石记录中的古流量:几何标度和实用取样标准
从地质野外观测中量化古流量仍然是一个关键的研究挑战。古流量与河道形态(宽度)的尺度关系;深度)已开发用于河流和河流三角洲。以前的古流量标度关系是基于流量-集水区标度和经验流速估计(如ch、曼宁公式)乘以河道截面积来计算流量的。在三角洲,海水(波、潮)能导致分流河道内的双向流动,现有的古流量标度关系由于单向流动假设而不适用。本文对全球114个现代河流三角洲的分布河道宽度的空间变异性进行了评估,以了解海洋对分布河道宽度影响的极限。利用6213次河道宽度测量结果,各三角洲的分流河道宽度中值与河占主导、潮占主导和波浪占主导的三角洲的河岸流量相关,后两者包括双向水流的影响。对于河流和波浪主导的三角洲,得出了统计上显著的宽度-流量比例关系,而对于潮汐主导的三角洲,没有发现显著的关系。通过对现代三角洲测量的河道宽度进行反向自举,估计河流三角洲上游和波浪三角洲上游用于古三角洲沉积的宽度-流量尺度关系所需的最小宽度测量次数分别为3次和4次,而河流三角洲下游则增加到30次。这些估计将指导沉积学研究,这些研究通常在岩石记录中暴露的分流河道宽度数量有限。为了验证岩石记录中这些可选宽度-流量尺度关系的可靠性,我们对美国白垩纪Mesa Rica砂岩组进行了古流量估算。将这些结果与更为复杂的ch逍遥法进行比较,表明这些新的标度关系是准确的。因此,有人提出,从现代三角洲获得的标度关系可以应用于岩石记录,比以前发表的方法需要更少、更容易测量的数据输入。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
CiteScore
3.80
自引率
5.00%
发文量
50
审稿时长
3 months
期刊介绍: The journal is broad and international in scope and welcomes contributions that further the fundamental understanding of sedimentary processes, the origin of sedimentary deposits, the workings of sedimentary systems, and the records of earth history contained within sedimentary rocks.
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