Exploring the potential of rock surface luminescence from glacial sediments: dating and transport history

IF 2.4 3区 地球科学 Q2 GEOGRAPHY, PHYSICAL
Boreas Pub Date : 2024-01-31 DOI:10.1111/bor.12648
Eike F. Rades, Reza Sohbati, Helena Alexanderson, Mayank Jain, Andrew S. Murray
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引用次数: 0

Abstract

The dating of moraine deposits can present challenges to standard geochronological methods; terrestrial cosmogenic nuclide (TCN), sediment luminescence and radiocarbon dating may suffer from problems of incomplete resetting (by inheritance, intermittent cover/exposure, transport under unfavourable conditions) and/or a lack of suitable (organic) material. Rock surface luminescence burial dating (RSLBD) offers an alternative approach with considerable potential in dating moraines. In RSLBD, large cobbles/boulders are targeted, rather than smaller grains usually used in luminescence dating. The age limit of RSLBD is much higher than that of radiocarbon dating, and rocks are much more readily available than organic material. In contrast to TCN dating, the effect of exposure prior to deposition can be measured. In this study, we sampled a broad selection of primarily granitic boulders of various sizes and shapes (e.g. different degrees of roundness and sphericity) from the Vimmerby Moraine, a prominent and accessible feature in southern Sweden dated using TCN to 14.4±0.9 ka. Our study was designed to test whether morphological characteristics can be used to discriminate in favour of the most light-exposed boulders and minimize measurements of non-exposed boulders. As expected, not all RSLBD ages can be attributed to the same depositional event, but the majority of the resulting ages provide a mean age of 13.0±1.5 ka, consistent with the cosmogenic nuclide dating of the Vimmerby Moraine. Despite the apparently successful TCN study, the luminescence–depth profiles measured in the buried surfaces of the sampled clasts indicate that >50% of these moraine boulders were exposed to light (and cosmic radiation) before final deposition, implying some (presumably small) TCN inheritance; seven of the 16 boulders identified as light exposed were sufficiently bleached to be useful for RSLBD. These results and their implications in regard to transport and deposition of the sampled cobbles are critically discussed and evaluated.

Abstract Image

探索冰川沉积物岩石表面发光的潜力:年代测定和迁移历史
冰碛沉积物的年代测定对标准地质年代学方法提出了挑战;陆地宇宙成因核素(TCN)、沉积物发光和放射性碳年代测定可能会受到不完全复位(继承、间歇性覆盖/暴露、不利条件下的迁移)和/或缺乏合适(有机)材料的影响。岩石表面发光埋藏测年法(RSLBD)提供了另一种方法,在确定冰碛物的年代方面具有相当大的潜力。在 RSLBD 中,目标是大卵石/巨石,而不是通常用于发光测年的小颗粒。RSLBD 的年龄限制比放射性碳测年高得多,而且岩石比有机材料更容易获得。与 TCN 测定法不同的是,RSLBD 可以测量沉积前暴露的影响。在这项研究中,我们从维默比冰碛(Vimmerby Moraine)采集了大量主要是花岗岩巨石的样本,这些巨石具有不同的大小和形状(例如不同程度的圆度和球度),维默比冰碛是瑞典南部一个突出且容易到达的地貌,采用 TCN 测定的年代为 14.4±0.9 ka。我们的研究旨在检验形态特征是否可用于区分受光最多的巨石,并尽量减少对未受光巨石的测量。不出所料,并不是所有的 RSLBD 年龄都能归因于同一沉积事件,但得出的大多数年龄的平均年龄为(13.0±1.5)ka,与维默比冰碛的宇宙成因核素测年结果一致。尽管 TCN 研究显然是成功的,但在取样碎屑埋藏表面测量到的发光深度剖面表明,这些冰碛巨石中有 50% 在最终沉积之前暴露在光线(和宇宙辐射)下,这意味着有一些(可能很小)TCN 遗传;在被确定为暴露在光线下的 16 块巨石中,有 7 块的漂白程度足以用于 RSLBD。我们对这些结果及其对取样卵石的迁移和沉积的影响进行了认真的讨论和评估。
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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