Quantitative analysis of crevasse-splay systems from modern fluvial settings

IF 2 4区 地球科学 Q1 GEOLOGY
M. Rahman, J. Howell, D. Macdonald
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引用次数: 5

Abstract

Although crevasse splays are a common constituent of many fluvial and fluvio-deltaic systems, they remain less well understood than the channel deposits in those settings, especially with respect to controls on their occurrence, distribution, and geometry. The current study aims to redress this balance and investigate controls on 1) splay formation and occurrence and 2) splay size and geometry. The study has used Google Earth-based satellite imagery to examine crevasse-splay deposits from eight modern fluvial systems. A total of 1556 crevasse splays were identified using imagery from 1984 to 2020. Most of the splays (c. 70%) occur on the outer sinuous river bank with offtake angles ranging from 10° to 140° (mean 75°) to the channel flow direction. Three different types of splays have been identified: i) single crevasse splays, ii) laterally amalgamated crevasse splays, and iii) crevasse-splay complexes. The areal extent of splay bodies varies widely and ranges from less than 1 km2 up to 221 km2. The single crevasse splays are the primary and smallest form of splay, with an average area of 0.61 km2. Compensational stacking or progradation significantly increase the splay area and form laterally amalgamated splays and splay complexes, respectively. The average areal extent of laterally amalgamated splays is 1.33 km2, and of splay complexes, 39 km2. The climate, discharge, floodplain morphology, vegetation, trunk channel slope, sinuosity, and sediment load primarily control the occurrence, geometry, and dimensions of crevasse splays. Results demonstrate that sparse or no floodplain vegetation favors the formation of elongated tongue-shaped crevasse splays while densely vegetated floodplains produce more lobate splays. The highest splay frequency occurs in systems where the river experiences sudden high magnitude variation in discharge, has a low cross-sectional area, and noncohesive bank materials. Larger splay size is correlated with lower river slope angles and higher sinuosity, discharge, and floodplain relief. Channel size has little influence on the extent of splays. This work suggests that autogenic factors such as trunk-channel slope and sinuosity are more influential in arid–semiarid settings while allogenic factors such as discharge are important in temperate–equatorial settings.
现代河流环境下决口扇系统的定量分析
尽管裂缝裂缝是许多河流和河流三角洲体系的共同组成部分,但与河道沉积相比,人们对它们的了解仍然较少,特别是在对它们的产状、分布和几何形状的控制方面。目前的研究旨在纠正这种平衡,并研究1)裂缝形成和发生以及2)裂缝大小和几何形状的控制因素。这项研究使用了谷歌地球卫星图像来检查来自八个现代河流系统的裂缝-裂缝沉积物。利用1984年至2020年的图像,共确定了1556个裂缝。大部分(约70%)分布在蜿蜒的河堤外侧,与河道流向夹角在10°~ 140°(平均75°)之间。已经确定了三种不同类型的裂缝:i)单一裂缝裂缝,ii)横向合并裂缝裂缝,以及iii)裂缝-裂缝复合。扇形体的面积范围变化很大,从不足1平方公里到221平方公里不等。单裂缝展布是最主要的最小的展布形式,平均面积为0.61 km2。补偿性叠加或递进可显著增加展布面积,并分别形成横向混合展布和展布复合物。横向混合带状带的平均面积为1.33 km2,而横向混合带状带的平均面积为39 km2。气候、流量、洪泛平原形态、植被、干流坡度、曲度和泥沙负荷主要控制着裂缝裂缝的发生、几何形状和大小。结果表明,稀疏或无植被的洪泛平原有利于形成细长舌状裂缝,而植被密集的洪泛平原则形成更多的叶状裂缝。当河流的流量突然发生大幅度变化、横截面积小、河岸材料不粘连时,会出现最高的张开频率。较大的张开尺寸与较低的河坡角、较高的曲度、流量和洪泛平原起伏度有关。通道大小对发散的程度影响不大。该研究表明,干旱区和半干旱区河道坡度和弯曲度等自生因子的影响更大,而在温带-赤道区,流量等异体因子的影响更大。
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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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