Paleoslope Reconstruction In Sandy Suspended-Load-Dominant Rivers
Paleoslope Reconstruction In Sandy Suspended-Load-Dominant Rivers
复制标题
沙质悬荷载主导河流的古坡重建
DOI：
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
P. Heller
中科院分区：
文献类型：
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作者：
R. Lynds;D. Mohrig;E. Hajek;P. Heller
约束古冲积河流系统的沉积梯度，可以帮助重建景观和估计古流量，通过建立大陆层序的气候和构造历史的边界。我们提出了三种方法来估计古代沉积梯度的基础上的解释模式的沉积物运输的范围内发现的颗粒大小的床的现代河流或保存在通道填充。对于以悬浮物为主要输沙方式的桑迪河流，这些方法利用了可直接从保存地层获得的观测结果，包括古水流深度和粒度的测量。第一种方法将河流坡度与平滩流时的希尔兹数联系起来。第二种方法与第一种方法相似，但允许平滩流时希尔兹数随粒径变化。最后一种方法依赖于同一系统中悬浮泥沙和床沙泥沙输移所需的标准，是最全面和物理上合理的方法。我们提出了每种方法，并用现代河流数据集对其进行测试，以验证准确性并帮助约束不确定性-这是使其适应古代系统的第一步。结果表明，所有的方法估计斜率的一个因素内的两个。这些方法是潜在的非常强大的解释桑迪河流沉积，因为他们可以提供相当准确的定量估计古坡度，一个难以捉摸的，但重要的环境变量。
Constraining the depositional gradient of ancient alluvial river systems can aid in reconstructing landscapes and estimating paleodischarge by establishing boundaries on the climatic and tectonic history of continental sequences. We present three methods for estimating ancient depositional gradients based on the interpreted mode of sediment transport for the range of particle sizes found on the beds of modern rivers or preserved in channel fills. For sandy rivers with suspension as the dominant mode of sediment transport, these methods take advantage of observations that can be directly obtained from preserved strata, including measurements of paleo flow depth and grain size. The first method relates river slope to Shields number at bankfull flow. The second method is similar to the first but allows for variation in Shields number at bankfull flow with grain diameter. The final method relies on criteria required for both suspended- and bed-material load sediment transport in the same system and is the most comprehensive and physically justified method. We present each method and test them with modern river datasets to verify accuracy and help constrain uncertainty—the first step to adapting them to ancient systems. Results indicate that all methods estimate slope within a factor of two. These methods are potentially very powerful for interpreting sandy fluvial deposits because they can provide reasonably accurate quantitative estimates of paleoslope, an elusive yet important environmental variable.