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DOI	10.1016/j.epsl.2021.117092
	Moraine crest or slope: An analysis of the effects of boulder position on cosmogenic exposure age
	Tomkins M.D.; Dortch J.M.; Hughes P.D.; Huck J.J.; Pallàs R.; Rodés Á.; Allard J.L.; Stimson A.G.; Bourlès D.; Rinterknecht V.; Jomelli V.; Rodríguez-Rodríguez L.; Copons R.; Barr I.D.; Darvill C.M.; Bishop T.
发表日期	2021
ISSN	0012821X
卷号	570
英文摘要	Terrestrial cosmogenic nuclide dating of ice-marginal moraines can provide unique insights into Quaternary glacial history. However, pre- and post-depositional exposure histories of moraine boulders can introduce geologic uncertainty to numerical landform ages. To avoid geologic outliers, boulders are typically selected based on their depositional context and individual characteristics but while these criteria have good qualitative reasoning, many have not been tested quantitatively. Of these, boulder location is critical, as boulders located on moraine crests are prioritised, while those on moraine slopes are typically rejected. This study provides the first quantitative assessment of the relative utility of moraine crest and moraine slope sampling using new and published 10Be and 36Cl ages (n = 19) and Schmidt hammer sampling (SH; n = 635 moraine boulders, ∼19,050 SH R-values) in the northern and southern Pyrenees. These data show that for many of the studied moraines, the spatial distribution of “good” boulders is effectively random, with no consistent clustering on moraine crests, ice-proximal or -distal slopes. In turn, and in contrast to prior work, there is no clear penalty to either moraine crest or moraine slope sampling. Instead, we argue that landform stability exerts a greater influence on exposure age distributions than the characteristics of individual boulders. For the studied landforms, post-depositional stability is strongly influenced by sedimentology, with prolonged degradation of matrix-rich unconsolidated moraines while boulder-rich, matrix-poor moraines stabilised rapidly after deposition. While this pattern is unlikely to hold true in all settings, these data indicate that differences between landforms can be more significant than differences at the intra-landform scale. As ad hoc assessment of landform stability is extremely challenging based on geomorphological evidence alone, preliminary SH sampling, as utilised here, is a useful method to assess the temporal distribution of boulder exposure ages and to prioritise individual boulders for subsequent analysis. © 2021 Elsevier B.V.
关键词	cosmogenic nuclides degradation geologic uncertainty moraine Schmidt hammer weathering
英文关键词	Deposition; Geomorphology; Hammers; Isotopes; Landforms; Matrix algebra; Cosmogenic exposure; Cosmogenic nuclide dating; Cosmogenic nuclides; Exposure age; Geologic uncertainty; matrix; Moraine; Moraine boulders; Schmidt hammer; Terrestrial cosmogenic nuclides; Weathering
语种	英语
来源期刊	Earth and Planetary Science Letters
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/203315
作者单位	Department of Geography, University of Manchester, Manchester, M13 9PL, United Kingdom; Cryosphere Research at Manchester, Manchester, United Kingdom; Kentucky Geological Survey, University of Kentucky, Lexington, United States; Departament de Dinàmica de la Terra i de l'Oceà, Universitat de Barcelona, Barcelona, 08028, Spain; Scottish Universities Environmental Research Centre, Rankine Avenue, East Kilbride, G75 0QF, United Kingdom; Aix-Marseille Univ., CNRS, IRD, INRA, Coll France, UM 34 CEREGE, Technopôle de l'Environnement Arbois-Méditerranée, BP80, Aix-en-Provence, 13545, France; Dpto. Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Avenida de los Castros s/n, Santander, 39005, Spain; Snow and Mountain Research Centre of Andorra (CENMA), Andorran Research Institute (IEA), Sant Julià de Lòria, Andorra; Department of Natural Sciences, Manchester Metropolitan University, Manchester, United Kingdom
推荐引用方式 GB/T 7714	Tomkins M.D.,Dortch J.M.,Hughes P.D.,et al. Moraine crest or slope: An analysis of the effects of boulder position on cosmogenic exposure age[J],2021,570.
APA	Tomkins M.D..,Dortch J.M..,Hughes P.D..,Huck J.J..,Pallàs R..,...&Bishop T..(2021).Moraine crest or slope: An analysis of the effects of boulder position on cosmogenic exposure age.Earth and Planetary Science Letters,570.
MLA	Tomkins M.D.,et al."Moraine crest or slope: An analysis of the effects of boulder position on cosmogenic exposure age".Earth and Planetary Science Letters 570(2021).