气候变化领域集成服务门户(CCPortal): Influence of extreme and annual floods on point-bar sedimentation: Inferences from Powder River, Montana, USA

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DOI	10.1130/B31990.1
	Influence of extreme and annual floods on point-bar sedimentation: Inferences from Powder River, Montana, USA
	Ghinassi M.; Moody J.; Martin D.
发表日期	2019
ISSN	167606
起始页码	71
结束页码	83
卷号	131 期号:2021-01-02
英文摘要	Effects of discharge variability on pointbar sedimentation are not well documented, although resulting changes in flow patterns are well known. This paper focuses on a meander of Powder River in Montana (USA). In May 1978, Powder River had a 50- year recurrence flood, which caused outer bank retreat of ~70 m. This bank continued to retreat over ~40 m in response to annual floods between 1979 and 2016. A trench, up to 2 m deep and 60 m long, was excavated in 2016 through the axial point-bar deposits accumulated during and since the 1978 flood. Deposits from the extreme 1978 flood consisted of stratified, coarsening-upward pebbles with subordinate sand, and show paleoflow toward the outer bank. Deposits accreted during subsequent annual floods consist of fining-upward, medium to fine sand with subordinate mud and gravel. These deposits contain sedimentary structures indicating transport from the channel up the bar. Field observations indicate that during extreme floods, the axial part of the bar was armored by coarsening-upward gravels and not affected by secondary helical circulation. In contrast, during annual floods, armoring was not observed and most of the flow was directed up the sloping pointbar surface, indicating secondary circulation near the bend apex. This paper shows that the area affected by the secondary helical circulation shifts downstream and upstream of the bend apex during extreme and annual floods, respectively. This causes significant changes in grain size and sedimentary facies distribution in point-bar deposits, which should be considered when analyzing meandering- river deposits in the ancient sedimentary record. © 2018 Geological Society of America.
语种	英语
来源期刊	Bulletin of the Geological Society of America
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/184975
作者单位	Department of Geosciences, University of Padova, V. Gradenigo 6, Padova, 35131, Italy; U.S. Geological Survey, 3215 Marine St., Suite E-127, Boulder, CO 80303, United States
推荐引用方式 GB/T 7714	Ghinassi M.,Moody J.,Martin D.. Influence of extreme and annual floods on point-bar sedimentation: Inferences from Powder River, Montana, USA[J],2019,131(2021-01-02).
APA	Ghinassi M.,Moody J.,&Martin D..(2019).Influence of extreme and annual floods on point-bar sedimentation: Inferences from Powder River, Montana, USA.Bulletin of the Geological Society of America,131(2021-01-02).
MLA	Ghinassi M.,et al."Influence of extreme and annual floods on point-bar sedimentation: Inferences from Powder River, Montana, USA".Bulletin of the Geological Society of America 131.2021-01-02(2019).