The granite tors of Dartmoor, Southwest England: rapid and recent emergence revealed by Late Pleistocene cosmogenic apparent exposure ages

Gunnell, Yanni; Jarman, David; Braucher, Régis; Calvet, Marc; Delmas, Magali; Léanni, Laettitia; Bourlès, Didier; Arnold, Maurice; Aumaître, Georges; Keddaouche, Karim

doi:10.1016/j.quascirev.2012.11.005

Cited by 36 publications

(22 citation statements)

References 43 publications

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“…Several authors estimated the exposure ages of such landforms. In most cases, however, only samples at the top of tors/boulders were analysed (e.g., Bierman & Caffee, 2001;Darmody et al, 2008;Gunnell et al, 2013). A more detailed sampling design has very rarely been applied ( rates can be determined with nuclear fallout radionuclides (Lal, Tims, Fifield, Wasson, & Howe, 2013;Meusburger et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Denudation variability of the Sila Massif upland (Italy) from decades to millennia using ¹⁰Be and ^239+240Pu

et al. 2018

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Landscapes and soils evolve in non‐linear ways over millennia. Current knowledge is incomplete as only average denudation (or erosion) rates are normally estimated, neglecting the temporal discontinuities of these processes. The determination of regressive and progressive phases of soil evolution is important to our understanding of how soils and landscapes respond to environmental changes. The Sila Massif (Italy) provides a well‐defined geomorphological and geological setting to unravel temporal variations in soil redistribution rates. We used a combination of in situ cosmogenic radionuclide measurements (10Be) along tor (residual rock) height profiles, coupled with fallout radionuclides (239+240Pu) in soils, to model soil denudation rates over the last 100 ka. We measured rates prior to the Last Glacial Maximum (LGM) of ≤30 t km−2 yr−1 (~0.036 mm yr−1). Following the LGM, during the transition from the Pleistocene to the Holocene, these rates increased to ~150–200 t km−2 yr−1 and appeared to be above soil production rates, causing regressive soil evolution. For the last ~50 years, we even describe erosion rates of ≥1,000 t km−2 yr−1 (~1.23 mm yr−1) and consider human impact as the decisive factor for this development. Consequently, the natural soil production rates cannot cope with the current erosion rates. Thus, a distinct regressive phase of soil formation exists, which will give rise to shallowing of soils over time. Overall, our multimethod approach traced denudation and erosion histories over geologic and human timescales and made a new archive to soil science and geomorphology accessible.

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Section: Introductionmentioning

confidence: 99%

Denudation variability of the Sila Massif upland (Italy) from decades to millennia using ¹⁰Be and ^239+240Pu

et al. 2018

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“…A search of the literature shows that surface denudation rates using granite tors are about 0.01–0.02 mm yr ‐1 for cold (alpine) regions (Small et al ., ) and 0.01–0.09 mm yr ‐1 in cool temperate climates (Heimsath et al ., ; Phillips et al ., ; Gunnell et al ., ). Our average exhumation rates (0.03–0.10 mm yr ‐1 ) fit well to those reported from the Dartmoor tors (Gunnell et al ., ). Using river sediments as tracers, Olivetti et al .…”

Section: Discussionmentioning

confidence: 99%

“…A search of the literature shows that surface denudation rates using granite tors are about 0.01-0.02 mm yr -1 for cold (alpine) regions (Small et al, 1999) and 0.01-0.09 mm yr -1 in cool temperate climates (Heimsath et al, 2001;Phillips et al, 2006;Gunnell et al, 2013). Our average exhumation rates (0.03-0.10 mm yr -1 ) fit well to those reported from the Dartmoor tors (Gunnell et al, 2013). Using river sediments as tracers, Olivetti et al (2012) reported similar average erosion rates from cosmogenic 10 Be concentrations for the low-relief surfaces of the Sila upland (0.09 ± 0.01 to 0.13 ± 0.01 mm yr -1 ).…”

Section: Torsmentioning

confidence: 99%

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Climate and relief‐induced controls on the temporal variability of denudation rates in a granitic upland

Raab

Egli

Norton

et al. 2019

Earth Surf Processes Landf

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How soil erosion rates evolved over the last about 100 ka and how they relate to environmental and climate variability is largely unknown. This is due to a lack of suitable archives that help to trace this evolution. We determined in situ cosmogenic beryllium‐10 (10Be) along vertical landforms (tors, boulders and scarps) on the Sila Massif to unravel their local exhumation patterns to develop a surface denudation model over millennia. Due to the physical resistance of tors, their rate of exhumation may be used to derive surface and, thus, soil denudation rates over time. We derived soil denudation rates that varied in the range 0–0.40 mm yr‐1. The investigated boulders, however, appear to have experienced repositioning processes about ~20–25 ka bp and were therefore a less reliable archive. The scarps of the Sila upland showed a rapid bedrock exposure within the last 8–15 ka. Overall, the denudation rates increased steadily after 75 ka bp but remained low until about 17 ka bp. The exhumation rates indicate a denudation pulse that occurred about 17–5 ka bp. Since then the rates have continuously decreased. We identify three key factors for these developments – climate, topography and vegetation. Between 75 and 17 ka bp, climate was colder and drier than today. The rapid changes towards warmer and humid conditions at the Pleistocene–Holocene transition apparently increased denudation rates. A denser vegetation cover with time counteracted denudation. Topography also determined the extent of denudation rates in the upland regime. On slopes, denudation rates were generally higher than on planar surfaces. By determining the exhumation rates of tors and scarps, soil erosion rates could be determined over long timescales and be related to topography and particularly to climate. This is key for understanding geomorphic dynamics under current environmental settings and future climate change. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.

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“…The characteristics of sheeting joints in the Cairngorm tors support the application of either Palmer and Nielsen's [1962] single-stage model or Hall and Phillips' [2006] intermediate model to the formation of these tors. Although Linton's [1955] two-stage model was developed from observations of the Dartmoor tors, the presence in those tors of closely spaced (few tens of centimeters) sheeting joints that mirror surrounding ground surfaces [Ehlen, 1992;Plate 3.7 in Migoń, 2006, p. 101;Gunnell et al, 2013] again supports the application of either of the alternative two models to the formation of these tors. These important implications of sheet jointing have been previously unrecognized in the tor literature and probably also apply to sheeted tors elsewhere.…”

Section: 1002/2013jf002862mentioning

confidence: 99%

Controls of tor formation, Cairngorm Mountains, Scotland

et al. 2014

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Tors occur in many granitic landscapes and provide opportunities to better understand differential weathering. We assess tor formation in the Cairngorm Mountains, Scotland, by examining correlation of tor location and size with grain size and the spacing of steeply dipping joints. We infer a control on these relationships and explore its potential broader significance for differential weathering and tor formation. We also assess the relationship between the formation of subhorizontal joints in many tors and local topographic shape by evaluating principle surface curvatures from a digital elevation model of the Cairngorms. We then explore the implications of these joints for tor formation. We conclude that the Cairngorm tors have formed in kernels of relatively coarse grained granite. Tor volumes increase with grain size and the spacing of steeply dipping joints. We infer that the steeply dipping joints largely formed during pluton cooling and are more widely spaced in tor kernels because of slower cooling rates. Preferential tor formation in coarser granite with a wider joint spacing that is more easily grusified indicates that joint spacing is a dominant control on differential weathering. Sheet jointing is well developed in tors located on relatively high convex surfaces. This jointing formed after the gross topography of the Cairngorms was established and before tor emergence. The presence of closely spaced (tens of centimeters), subhorizontal sheeting joints in tors indicates that these tors, and similarly sheeted tors elsewhere, formed either after subaerial exposure of bedrock or have progressively emerged from a regolith only a few meters thick.

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The granite tors of Dartmoor, Southwest England: rapid and recent emergence revealed by Late Pleistocene cosmogenic apparent exposure ages

Cited by 36 publications

References 43 publications

Denudation variability of the Sila Massif upland (Italy) from decades to millennia using ¹⁰Be and ^239+240Pu

Denudation variability of the Sila Massif upland (Italy) from decades to millennia using ¹⁰Be and ^239+240Pu

Climate and relief‐induced controls on the temporal variability of denudation rates in a granitic upland

Controls of tor formation, Cairngorm Mountains, Scotland

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The granite tors of Dartmoor, Southwest England: rapid and recent emergence revealed by Late Pleistocene cosmogenic apparent exposure ages

Cited by 36 publications

References 43 publications

Denudation variability of the Sila Massif upland (Italy) from decades to millennia using 10Be and 239+240Pu

Denudation variability of the Sila Massif upland (Italy) from decades to millennia using 10Be and 239+240Pu

Climate and relief‐induced controls on the temporal variability of denudation rates in a granitic upland

Controls of tor formation, Cairngorm Mountains, Scotland

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Product

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Denudation variability of the Sila Massif upland (Italy) from decades to millennia using ¹⁰Be and ^239+240Pu

Denudation variability of the Sila Massif upland (Italy) from decades to millennia using ¹⁰Be and ^239+240Pu