Stratigraphy and age of a Neoglacial sedimentary succession of proglacial outwash and an alluvial fan in Langedalen, Veitastrond, western Norway

IF 2.4 3区 地球科学 Q2 GEOGRAPHY, PHYSICAL
Boreas Pub Date : 2022-11-01 DOI:10.1111/bor.12608
Atle Nesje, Denise C. Rüther, Jacob C. Yde
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Abstract

This study presents the sedimentary succession of an outwash plain and an alluvial fan located along the valley Langedalen at the south-eastern side of the Jostedalsbreen ice cap in inner Sogn, western Norway. A newly exposed ~2.8-m-high section along the southern riverbank of Langedøla river shows alternating layers of minerogenic sediments and peat layers with tree logs, identified as Salix sp. The section is situated in the distal part of an alluvial fan built out from the southern slope of Langedalen. Six AMS radiocarbon dates of tree fragments indicate that the accumulation of the fine-grained sediments in the lower part of the section was initiated earlier than the basal radiocarbon date of 914–976 calibrated years CE (1σ age range). These basal, fine-grained sediments are interpreted as proglacial outwash deposited in a floodplain depression or abandoned river channel in a low-energy glaciofluvial environment. Periods of low glacier cover, low river discharge or low-water stands over the floodplain allowed peat formation and the growth of trees and shrubs in the valley. The radiocarbon dates further indicate relatively rapid sediment accretion (~2.7–3 cm a−1) between 190 and 125 cm below the sediment surface, equivalent to approximately 1220 to 1250 cal. a CE (1σ age range). At ~60 cm depth below the surface, dated to approximately 1590 to 1620 cal. a CE (1σ age range), a transition to more coarse-grained, sandy and gravelly sediments indicates increased sediment supply and distal expansion of the alluvial fan. This occurred most likely as a consequence of increased sediment yield from expanding glaciers along the southern valley side of Langedalen as a response to the initial Little Ice Age glacier growth. Based on these results, the accretion and progradation of glacier-fed alluvial fans mainly occur during periods of glacier advance rather than during glacier recession.

Abstract Image

挪威西部Veitastrond Langedalen地区前冰期冲洗液和冲积扇新冰期沉积序列的地层学和时代
本研究展示了位于挪威西部内索恩Jostedalsbreen冰帽东南侧Langedalen山谷沿岸的冲积扇和冲积平原的沉积序列。Langedøla河南岸一个新暴露的约2.8米高的河段显示出交替的成矿沉积物层和泥炭层,这些沉积物和泥炭层被鉴定为Salix sp.。该河段位于Langedalen南坡形成的冲积扇的远端。树木碎片的六个AMS放射性碳年代表明,剖面下部细粒沉积物的堆积早于914-976年的基础放射性碳年代 校准年份CE(1σ年龄范围)。这些基底细粒沉积物被解释为沉积在低能量冰川河流环境中的洪泛平原凹陷或废弃河道中的前冰川沉积。低冰川覆盖、低河流流量或泛滥平原上的枯水期允许泥炭的形成以及山谷中树木和灌木的生长。放射性碳年代进一步表明沉积物堆积相对较快(~2.7-3 厘米 a−1)在190和125之间 沉积物表面以下cm,相当于约1220至1250 cal.a CE(1σ年龄范围)。约60 地表以下cm深度,年代约为1590年至1620年 cal.a CE(1σ年龄范围),向更粗粒、砂质和砾石沉积物的过渡表明沉积物供应增加,冲积扇向远端扩张。这很可能是由于Langedalen南部山谷一侧冰川扩张导致沉积物产量增加的结果,这是对小冰河时代冰川最初生长的回应。基于这些结果,冰川冲积扇的吸积和前积主要发生在冰川前进期,而不是冰川退缩期。
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
Boreas
Boreas 地学-地球科学综合
CiteScore
5.90
自引率
4.50%
发文量
36
审稿时长
>12 weeks
期刊介绍: Boreas has been published since 1972. Articles of wide international interest from all branches of Quaternary research are published. Biological as well as non-biological aspects of the Quaternary environment, in both glaciated and non-glaciated areas, are dealt with: Climate, shore displacement, glacial features, landforms, sediments, organisms and their habitat, and stratigraphical and chronological relationships. Anticipated international interest, at least within a continent or a considerable part of it, is a main criterion for the acceptance of papers. Besides articles, short items like discussion contributions and book reviews are published.
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