Rapid age assessment of glacial landforms in the Pyrenees using Schmidt hammer exposure dating (SHED)

Tomkins, Matt D.; Dortch, Jason M.; Hughes, Philip D.; Huck, Jonny; Stimson, Andrew; Delmas, Magali; Calvet, Marc; Pallàs, Raimón

doi:10.1017/qua.2018.12

Cited by 45 publications

(36 citation statements)

References 51 publications

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“…Unfortunately, geochronological data from Lough Nahanagan are clearly conflicting and indicate moraine deposition at either 11.5–11.6 ka ( n = 2; 14 C), 17.9 ± 1.0 ka ( n = 1; 36 Cl) or between 9.7 and 21.7 ka ( n = 3; 10 Be). While the limited number of samples ( n = 6) prevents statistically robust identification and rejection of erroneous results (Tomkins et al ., ), and in turn independent verification of SHED data at this site, the observed age scatter does highlight the importance of pre‐ or post‐depositional processes at Lough Nahanagan, with uncertainty introduced by moraine stabilization (Hallet and Putkonen, ), nuclide inheritance (Putkonen and Swanson, ) or a combination of both. At Kelly's Lough, 10 Be ages ( n = 6; Barth et al ., ) are also probably influenced by geological uncertainty and are non‐normally distributed, with ages of 9.5–9.7 ka ( n = 2), 11.2–11.7 ka ( n = 3) and one outlier age of 137 ± 7 ka.…”

Section: Resultssupporting

confidence: 57%

“…Moreover, given the long timescales of exposure (≥11 ka) and limited climatic variability across the relatively small mountain range (∼220 km 2 ), any differences in surface R ‐values due to lithology will probably be significantly smaller than the effect of variable exposure age. This interpretation is supported by large spatial scale 10 Be‐SH calibration curves from the British Isles (Tomkins et al , , ; n = 54; R 2 = 0.94, p < 0.01) and the Pyrenees (Tomkins et al , ; n = 52; R 2 = 0.96, p < 0.01) which indicate that the primary control on surface R ‐values is cumulative exposure to subaerial weathering. Instrument calibration (correction factor = 1.017) and age calibration (correction factor = 0.992) were performed using the SHED‐Earth online calculator (http://shed.earth) following the recommendations of Dortch et al .…”

Section: Methodsmentioning

confidence: 87%

“…C) and confirm deglaciation during the late YD or early Holocene. These independent 10 Be ages join a growing body of evidence that SHED can generate accurate ages for glacial landforms (Rode and Kellerer‐Pirklbauer, ; Ffoulkes and Harrison, ; Tomkins et al ., , ,).…”

Section: Resultsmentioning

confidence: 99%

“…All sampled surfaces were quartz‐rich, medium‐ to coarse‐grained Caledonian granite (GSI, ; Bedrock Geology; Scale 1: 500 000), with no clear spatial variability in grain size or rock composition. Although smaller‐scale geological maps indicate some variability between sampled sites (GSI, ; Bedrock Geology; Scale 1: 100 000), the predominant style of weathering is subaerial, as evidenced by granular disintegration of the rock surface (André, ; Tomkins et al , ). Although weathering rate variability cannot be excluded as an explanation for contrasting exposure age distributions across geological boundaries, it appears unlikely that these surfaces would weather at significantly different rates given their comparable grain size (1–5 mm), quartz content (∼20%), degree of lichen colonization and phenocryst size (≤30 mm).…”

Section: Methodsmentioning

confidence: 99%

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Timing of glacial retreat in the Wicklow Mountains, Ireland, conditioned by glacier size and topography

Tomkins

Dortch

Hughes

et al. 2018

J Quaternary Science

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Reconstructing the deglacial history of palaeo-glaciers provides vital information on retreat processes, information which can inform predictions of the future behaviour of many of the world's glaciers. On this basis, this paper presents 170 Schmidt Hammer exposure ages from moraine boulders and glacially sculpted bedrock to reveal the post-Last Glacial Maximum (LGM) history of the Wicklow Mountains, Ireland. These data suggest that large ice masses survived for 4-7 ka after retreat of the Irish Sea Ice Stream and were sustained by summit ice fields until $16.6 ka. Post-LGM retreat was driven by climate and involved numerous short-term ice front oscillations ( 1 ka), with widespread moraine deposition during Heinrich Stadial 1. In contrast, marked asynchroneity in the timing of Younger Dryas deglaciation is closely linked to snow redistribution which demonstrates the sensitivity of small cirque glaciers ( 1 km 2 ) to local topography. This result has important implications for palaeoclimate reconstructions as cirque glacier dynamics may be (at least partly) decoupled from climate. This is further complicated by post-depositional processes which can result in moraine ages (e.g. 10 Be) which post-date retreat. Future palaeoclimate studies should prioritize cirques where snow-contributing areas are small and where postdepositional disturbance of moraines is limited. Ã Area within the glacier drainage basin within the 210-300˚quadrant þ all other slopes which overlook the glacier (gradients >25˚).

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Section: Resultssupporting

confidence: 57%

Section: Methodsmentioning

confidence: 87%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

See 2 more Smart Citations

Timing of glacial retreat in the Wicklow Mountains, Ireland, conditioned by glacier size and topography

Tomkins

Dortch

Hughes

et al. 2018

J Quaternary Science

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“…In the Maladeta-Aneto Massif, there is a complete absence of tills between the innermost YD moraines and those of the LIA. Furthermore, some samples taken from polished areas recently deglaciated, upstream of the LIA moraines, delivered 10 Be exposure ages between 4.8 and 7.9 ka (Crest et al 2017), and Schmidt Hammer Exposure dating (SHED) between 4.1 and 5.2 (Tomkins et al 2018), demonstrating the strong heritage from the first half of the Holocene, and the relatively low erosive effect of the LIA glaciers. Nevertheless, geomorphological field work suggests the possible presence of moraines arising during the first Neoglacial pulses, for instance, the northern face of the Tendeñera Massif.…”

Section: Pre-lia Glacial Evolutionmentioning

confidence: 99%

Neoglaciation in the Spanish Pyrenees: a multiproxy challenge

et al. 2020

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Following the Holocene Thermal Maximum, dated between 11 and 6 ka, the Neoglacial period was one of the progressive, fluctuating cooling that peaked during the Little Ice Age (LIA). The almost total absence of glacial tills prior to the LIA in the Pyrenees forces recourse to a high variety of proxies, including lacustrine sediments, palynological records, dendroclimatology, ice cores from glaciers and caves, speleothems, historical documentation and glacial records. This has enabled us to identify several colder periods during the mid-and late-Holocene: (i) the first phase of the Neoglacial period occurred at some time around 6 ka; (ii) a glacial pulse immediately before 3.4 ka; (iii) a glacial re-advance during the Dark Ages, i.e., immediately before the Medieval Climate Anomaly, between the fourth and ninth centuries; and (iv) the Little Ice Age, which started at the beginning of the fourteenth century and finished in the mid-nineteenth century. During the LIA, there was remarkable climate variability, with two, and probably three, glacial pulses, mainly between 1620 and 1715 and in the first half of the nineteenth century. Of all of the Holocene cold periods, most of the European paleoclimatic records coincide on the occurrence of the LIA. For the remaining Holocene cold periods, European records show high variability and uncertainty, particularly for the onset of the Neoglacial, although the phases of glacial pulses in the Pyrenees broadly coincide with those identified in the Alps and northern Europe.

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Quantifying the effects of carborundum rock surface smoothing for Schmidt hammer R‐value metrics measured on glacial erratics in the North American Great Lakes region

Shepherd,

Portenga,

Peplinski

2024

Earth Surf Processes Landf

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Schmidt hammer R‐values, which reflect the degree of rock surface weathering, can be paired with independent rock surface exposure ages to produce Schmidt hammer exposure‐age dating (SHD) calibration curves that are used to provide rapid estimations of exposure ages for undated rock surfaces. In this Letter, we lay the groundwork for later establishing a SHD calibration curve based on glacial erratics deposited by the Laurentide Ice Sheet in the North American Great Lakes region. First, we establish a reference R‐value for a calibration boulder, which may be used to facilitate direct comparison of R‐values collected by different individuals using mechanical N‐type Schmidt hammers, specifically. We then assess how no, light or heavy use of a carborundum puck to smooth rock surfaces affects resulting R‐value data. Lastly, we compare two different R‐value metrics on the same rock surface: Rmean (n = 30) versus ΔR (Rmax − Rmin of five consecutive R‐values on the same spot). In all assessments, Rmean is similar for erratic surfaces with no and light surface treatment, and both are significantly lower than Rmean of surfaces with heavy treatment. Thus, we advise against the use of heavy surface treatment in SHD applications. We observe no relationship between inferred erratic age and either Rmean or ΔR, which could arise from inferred ages of erratics being inaccurate, from inferred ages of erratics being too similar or from measuring too few erratics from each landform.

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Rapid age assessment of glacial landforms in the Pyrenees using Schmidt hammer exposure dating (SHED)

Cited by 45 publications

References 51 publications

Timing of glacial retreat in the Wicklow Mountains, Ireland, conditioned by glacier size and topography

Timing of glacial retreat in the Wicklow Mountains, Ireland, conditioned by glacier size and topography

Neoglaciation in the Spanish Pyrenees: a multiproxy challenge

Quantifying the effects of carborundum rock surface smoothing for Schmidt hammer R‐value metrics measured on glacial erratics in the North American Great Lakes region

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