Browsing by Author "Fabel, D"

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    Characteristic cosmogenic nuclide concentrations in relict surfaces of formerly glaciated regions
    (Wiley, 2006-08-21) Stroeven, AP; Harbor, J; Fabel, D; Kleman, J; Hättestrand, C; Elmore, D; Fink, D
    This chapter contains sections titled: Significance of relict surfaces Characteristic cosmogenic nuclide concentrations in relict surfaces Conclusions © 2006 by Blackwell Science Ltd
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    Cosmogenic nuclide evidence for minimal erosion across two subglacial sliding boundaries of the late glacial Fennoscandian ice sheet
    (Elsevier, 2006-04) Harbor, J; Stroeven, AP; Fabel, D; Clarhäll, A; Kleman, J; Li, YK; Elmore, D; Fink, D
    The existence of sliding and frozen bed areas under ice sheets is significant in understanding basal thermal regimes, patterns of erosion and landform development, and in constraining boundary conditions for the reconstructions of ice sheets. Recognition of subglacial boundaries between sliding and frozen-bed areas for former ice sheets is typically based on distinct morphological contrasts between areas with glacial landform assemblages and relict areas showing little alteration of pre-existing features. Some of these boundaries, especially on continental shield areas, however, are clearly visible from air photos but have minimal topographic expression. Understanding the chronology and erosional development of such boundaries is important to provide insight into the pattern and persistence of basal conditions under ice sheets. Geomorphic evidence and cosmogenic radionuclide concentrations of bedrock outcrops on either side of two sliding boundaries on Ultevis and Arvestuottar, low-relief upland plateaus in northern Sweden, are consistent with negligible erosion in relict landscape (frozen bed) areas due to the last glaciation, but also indicate insignificant erosion in the sliding areas. Such a pattern and magnitude of landscape modification indicates that sliding was short lived in these areas, likely as a transient phase during deglaciation. These sites demonstrate that short periods of sliding are in some cases sufficient to produce landscapes that are recognized as ‘glacial’ from air photos. Thus, regions of sliding identified on shield areas must be viewed as the cumulative total area that has experienced sliding at any time during a glaciation. The actual extent of sliding areas during any single ice sheet phase is presumably considerably less than this cumulative total, which has important implications for establishing appropriate basal boundary conditions for ice sheet reconstructions.© 2005 Elsevier B.V.
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    Deglaciation of Fennoscandia
    (Elsevier, 2016-09-01) Stroeven, AP; Hättestrand, C; Kleman, J; Heyman, J; Fabel, D; Fredin, O; Goodfellow, BW; Harbor, JM; Jansen, JD; Olsen, L; Caffee, MW; Fink, D; Lundqvist, J; Rosqvist, GC; Strömberg, B; Jansson, KN
    To provide a new reconstruction of the deglaciation of the Fennoscandian Ice Sheet, in the form of calendar-year time-slices, which are particularly useful for ice sheet modelling, we have compiled and synthesized published geomorphological data for eskers, ice-marginal formations, lineations, marginal meltwater channels, striae, ice-dammed lakes, and geochronological data from radiocarbon, varve, optically-stimulated luminescence, and cosmogenic nuclide dating. This is summarized as a deglaciation map of the Fennoscandian Ice Sheet with isochrons marking every 1000 years between 22 and 13 cal kyr BP and every hundred years between 11.6 and final ice decay after 9.7 cal kyr BP. Deglaciation patterns vary across the Fennoscandian Ice Sheet domain, reflecting differences in climatic and geomorphic settings as well as ice sheet basal thermal conditions and terrestrial versus marine margins. For example, the ice sheet margin in the high-precipitation coastal setting of the western sector responded sensitively to climatic variations leaving a detailed record of prominent moraines and other ice-marginal deposits in many fjords and coastal valleys. Retreat rates across the southern sector differed between slow retreat of the terrestrial margin in western and southern Sweden and rapid retreat of the calving ice margin in the Baltic Basin. Our reconstruction is consistent with much of the published research. However, the synthesis of a large amount of existing and new data support refined reconstructions in some areas. For example, the LGM extent of the ice sheet in northwestern Russia was located far east and it occurred at a later time than the rest of the ice sheet, at around 17–15 cal kyr BP. We also propose a slightly different chronology of moraine formation over southern Sweden based on improved correlations of moraine segments using new LiDAR data and tying the timing of moraine formation to Greenland ice core cold stages. Retreat rates vary by as much as an order of magnitude in different sectors of the ice sheet, with the lowest rates on the high-elevation and maritime Norwegian margin. Retreat rates compared to the climatic information provided by the Greenland ice core record show a general correspondence between retreat rate and climatic forcing, although a close match between retreat rate and climate is unlikely because of other controls, such as topography and marine versus terrestrial margins. Overall, the time slice reconstructions of Fennoscandian Ice Sheet deglaciation from 22 to 9.7 cal kyr BP provide an important dataset for understanding the contexts that underpin spatial and temporal patterns in retreat of the Fennoscandian Ice Sheet, and are an important resource for testing and refining ice sheet models. © 2015 The Authors. Under a Creative Commons license.
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    Exposure ages from relict lateral moraines overridden by the Fennoscandian ice sheet
    (Cambridge University Press, 2006-01) Fabel, D; Fink, D; Fredin, O; Harbor, J; Land, M; Stroeven, AP
    Lateral moraines constructed along west to east sloping outlet glaciers from mountain centred, pre-last glacial maximum (LGM) ice fields of limited extent remain largely preserved in the northern Swedish landscape despite overriding by continental ice sheets, most recently during the last glacial. From field evidence, including geomorphological relationships and a detailed weathering profile including a buried soil, we have identified seven such lateral moraines that were overridden by the expansion and growth of the Fennoscandian ice sheet. Cosmogenic 10Be and 26Al exposure ages of 19 boulders from the crests of these moraines, combined with the field evidence, are correlated to episodes of moraine stabilisation, Pleistocene surface weathering, and glacial overriding. The last deglaciation event dominates the exposure ages, with 10Be and 26Al data derived from 15 moraine boulders indicating regional deglaciation 9600 ± 200 yr ago. This is the most robust numerical age for the final deglaciation of the Fennoscandian ice sheet. The older apparent exposure ages of the remaining boulders (14,600–26,400 yr) can be explained by cosmogenic nuclide inheritance from previous exposure of the moraine crests during the last glacial cycle. Their potential exposure history, based on local glacial chronologies, indicates that the current moraine morphologies formed at the latest during marine oxygen isotope stage 5. Although numerous deglaciation ages were obtained, this study demonstrates that numerical ages need to be treated with caution and assessed in light of the geomorphological evidence indicating moraines are not necessarily formed by the event that dominates the cosmogenic nuclide data. © University of Washington
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    Ice sheet erosion patterns in valley systems in northern Sweden investigated using cosmogenic nuclides
    (Wiley, 2005-08-30) Li, YK; Harbor, J; Stroeven, AP; Fabel, D; Kleman, J; Fink, D; Caffee, M; Elmore, D
    Erosion patterns associated with glaciation of trunk and hanging valley systems in northern Sweden were investigated using cosmogenic nuclide 10Be apparent exposure ages and inferred nuclide inheritance. Sequences of samples taken across valleys known to have been covered repeatedly by the Fennoscandian ice sheet revealed two primary patterns of erosion. In Vávlávágge the exposure age pattern is consistent with >2 m of glacial erosion during the last glacial cycle along the entire profile. At Rávtasvággi, Dievssavággi and Alisvággi, exposure ages in the valley bottom contrast with apparent exposure ages two to four times older on the valley sides. The older ages on the valley sides reflect cosmogenic nuclide inheritance due to limited (<2 m) bedrock erosion of the valley sides during the last glacial cycle. The pattern and scale of erosion in these valleys indicates that glacial valley formation is a result of multiple glacial cycles rather than the result of topographic modification during a single glacial cycle. Initial data comparing hanging valley and trunk valley sites do not show distinct differences in apparent exposure ages. Slightly older ages for samples from hanging valley bottoms may suggest nuclide inheritance indicating lower erosion than in trunk valley bottoms, as would be expected given the marked topographic step between hanging and trunk valleys. Although quantifying the amount of erosion depends on the assumed cosmogenic nuclide inheritance prior to the onset of erosion, the pattern of erosion is independent of this. Hence the observed pattern of cosmogenic nuclide concentrations provides constraints on spatial patterns of erosion and helps to refine understanding of the timing and extent of landform modification by glaciation. Copyright © 2005 John Wiley & Sons, Ltd.
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    Importance of sampling across an assemblage of glacial landforms for interpreting cosmogenic ages of deglaciation
    (Academic Press INC Elsevier, 2011-07-01) Stroeven, AP; Fabel, D; Harbor, J; Fink, D; Caffee, M; Dahlgren, T
    Deglaciation chronologies for some sectors of former ice sheets are relatively poorly constrained because of the paucity of features or materials traditionally used to constrain the timing of deglaciation. In areas without good deglaciation varve chronologies and/or without widespread occurrence of material that indicates the start of earliest organic radiocarbon accumulations suitable for radiocarbon dating, typically only general patterns and chronologies of deglaciation have been deduced. However, mid-latitude ice sheets that had warm-based conditions close to their margins often produced distinctive deglaciation landform assemblages, including eskers, deltas, meltwater channels and aligned lineation systems. Because these features were formed or significantly altered during the last glaciation, boulder or bedrock samples from them have the potential to yield reliable deglaciation ages using terrestrial cosmogenic nuclides (TCN) for exposure age dating. Here we present the results of a methodological study designed to examine the consistency of TCN-based deglaciation ages from a range of deglaciation landforms at a site in northern Norway. The strong coherence between exposure ages across several landforms indicates great potential for using TCN techniques on features such as eskers, deltas and meltwater channels to enhance the temporal resolution of ice-sheet deglaciation chronologies over a range of spatial scales. (C) 2011 University of Washington.
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    Landscape preservation under Fennoscandian ice sheets determined from in situ produced 10Be and 26Al
    (Elsevier, 2002-07-30) Fabel, D; Stroeven, AP; Harbor, J; Kleman, J; Elmore, D; Fink, D
    Some areas within ice sheet boundaries retain pre-existing landforms and thus either remained as ice free islands (nunataks) during glaciation, or were preserved under ice. Differentiating between these alternatives has significant implications for paleoenvironment, ice sheet surface elevation, and ice volume reconstructions. In the northern Swedish mountains, in situ cosmogenic 10Be and 26Al concentrations from glacial erratics on relict surfaces as well as glacially eroded bedrock adjacent to these surfaces, provide consistent last deglaciation exposure ages (∼8–13 kyr), confirming ice sheet overriding as opposed to ice free conditions. However, these ages contrast with exposure ages of 34–61 kyr on bedrock surfaces in these same relict areas, demonstrating that relict areas were preserved with little erosion through multiple glacial cycles. Based on the difference in radioactive decay between 26Al and 10Be, the measured nuclide concentration in one of these bedrock surfaces suggests that it remained largely unmodified for a minimum period of 845−418+461 kyr. These results indicate that relict areas need to be accounted for as frozen bed patches in basal boundary conditions for ice sheet models, and in landscape development models. Subglacial preservation also implies that source areas for glacial sediments in ocean cores are considerably smaller than the total area covered by ice sheets. These relict areas also have significance as potential long-term subglacial biologic refugia. © 2002 Elsevier Science B.V.
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    Lowland river responses to intraplate tectonism and climate forcing quantified with luminescence and cosmogenic 10Be
    (Elesevier Science BV, 2013-03-15) Jansen, JD; Nanson, GC; Cohen, TJ; Fujioka, T; Fabel, D; Larsen, JR; Codilean, AT; Price, DM; Bowman, HH; May, JH; Gliganic, LA
    Intraplate tectonism has produced large-scale folding that steers regional drainage systems, such as the 1600 km-long Cooper Ck, en route to Australia's continental depocentre at Lake Eyre. We apply cosmogenic Be-10 exposure dating in bedrock, and luminescence dating in sediment, to quantify the erosional and depositional response of Cooper Ck where it incises the rising Innamincka Dome. The detachment of bedrock joint-blocks during extreme floods governs the minimum rate of incision (17.4 +/- 6.5 mm/ky) estimated using a numerical model of episodic erosion calibrated with our 10Be measurements. The last big-flood phase occurred no earlier than similar to 112-121 ka. Upstream of the Innamincka Dome long-term rates of alluvial deposition, partly reflecting synclinal-basin subsidence, are estimated from 47 luminescence dates in sediments accumulated since similar to 270 ka. Sequestration of sediment in subsiding basins such as these may account for the lack of Quaternary accumulation in Lake Eyre, and moreover suggests that notions of a single primary depocentre at base-level may poorly represent lowland, arid-zone rivers. Over the period similar to 75-55 ka Cooper Ck changed from a bedload-dominant, laterally-active meandering river to a muddy anabranching channel network up to 60 km wide. We propose that this shift in river pattern was a product of base-level rise linked with the slowly deforming syncline-anticline structure, coupled with a climate-forced reduction in discharge. The uniform valley slope along this subsiding alluvial and rising bedrock system represents an adjustment between the relative rates of deformation and the ability of greatly enhanced flows at times during the Quaternary to incise the rising anticline. Hence, tectonic and climate controls are balanced in the long term. © 2013, Elsevier Ltd.
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    Pleistocene deglaciation chronology of the Amery Oasis and Radok Lake, northern Prince Charles Mountains, Antarctica
    (Elsevier, 2006-03-15) Fink, D; McKelvey, BC; Hambrey, M. J; Fabel, D; Brown, R
    The East Antarctic Ice Sheet is the largest ice mass on Earth with a capacity to raise global sea level by up to 65 m. As the Lambert Glacier–Amery Ice Shelf drainage system is the largest to reach the coast of Antarctica, quantifying its evolution over the Quaternary is a vital component in developing an understanding of the Antarctic response to future climate change. Here we present a deglaciation chronology based on 10Be and 26Al in situ cosmogenic exposure ages of the northern Prince Charles Mountains, which flank the Lambert Glacier–Amery system, and that records the progressive emergence of McLeod Massif and Radok Lake basin from beneath the Mac.Robertson Land lobe of the East Antarctic Ice Sheet. The exposure ages monotonically decrease with both decreasing altitude and increasing proximity to the Amery Ice Shelf at the Antarctic coast. Exposure ages from the crests of McLeod Massif near the edge the Amery Ice Shelf and from Fisher Massif, 75 km further inland, each at ∼1200 m above sea level, are 2.2 ± 0.3 and 1.9 ± 0.2 Ma, respectively, suggesting their continuous exposure above the ice sheet at least since close to the Plio–Pleistocene boundary. An extensive plateau at ∼800 m altitude on McLeod Massif above Battye Glacier records the massif's increased emergence above the ice sheet surface at about between 880 and 930 ka ago indicating 400 m of ice volume reduction in the mid Pleistocene. Correcting these apparent ages for a reasonable choice in erosion rate would extend this event to ∼1.15 Ma — a period identified from Prydz Bay ODP core-1167 when sedimentation composition alters and rates decrease 10-fold. Exposure ages from boulder-mantled erosional surfaces above and beyond the northern end of Radok Lake at 220 m, range from 28 to 121 ka. Independent of choice of model interpretation to explain this age spread, the most recent major reoccupation of Radok Lake by Battye Glacier ice occurred during the last glacial cycle. Moraine ridges at the lower altitude of 70–125 m were deposited during the final withdrawal of Battye Glacier ice from the lake basin between 11 and 20 ka ago. This new chronology indicates that the highest Amery Oasis peaks have not been overridden by the Mac.Robertson Land lobe of the East Antarctic Ice Sheet for at least the past 2 Ma. Since this time we document 3 major periods of regional reduction in ice sheet volume at ∼1.1 Ma, during the last glacial cycle (120 to 30 ka) and through the Last Glacial Maximum (20 to 10 ka) that resulted in an overall 1000 m of ice lowering in the Battye Glacier–Radok Lake region. © 2005 Elsevier B.V.
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    Pleistocene dynamics of the interior East Antarctic ice sheet
    (Geological Society of America, 2010-08) Lilly, K; Fink, D; Fabel, D; Lambeck, K
    Current models describing past configurations of the East Antarctic ice sheet are poorly constrained by observations. Exposure dating of bedrock surfaces using in situ–produced cosmogenic nuclides provides an ideal tool for directly constraining former changes in ice sheet elevation. We present cosmogenic radionuclide 10Be and 26Al measurements in bedrock surfaces and glacially transported cobbles in the Grove Mountains, a group of nunataks within the slow-flowing interior ice sheet dome, hundreds of kilometers from the coastal ice margin and from ice streams. Samples were collected in vertical transects over 500 m of relief. Minimum bedrock and erratic exposure ages show a trend of increasing age with height above the ice sheet, spanning a period from 0.3 to 4.0 Ma and 50–900 ka, respectively. No evidence was found for thicker ice at the Last Glacial Maximum compared to modern ice thickness. The older bedrock exposure ages of 2.5–4.0 Ma require steady-state erosion rates of <0.1 mm k.y.−1. The measured two-isotope bedrock exposure ages are successfully modeled when changes in surface elevation of the ice sheet are described by a combination of linear long-term ice surface lowering and shorter term high-frequency glacial-interglacial oscillations. The best-fit model requires a long-term thinning rate of 50 m m.y.−1 and an elevation change of 100 m over a 100 k.y. glacial cycle. © 2010, Geological Society of America
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    Preliminary results of CoQtz-N: a quartz reference material for terrestrial in-situ cosmogenic 10Be and 26A1 measurements
    (Elsevier, 2019-10-01) Binnie, SA; Dewald, A; Heinze, S; Voronina, E; Hein, AS; Wittmann, H; von Blanckenburg, F; Hetzel, R; Christl, M; Schaller, M; Léanni, L; ASTER Team; Hippe, K; Vockenhuber, C; Ivy-Ochs, S; Maden, C; Fülöp, RH; Fink, D; Wilcken, KM; Fujioka, T; Fabel, D; Freeman, SPHT; Xu, S; Fifield, LK; Akçar, N; Spiegel, C; Dunai, TJ
    There is growing interest in geochronological applications of terrestrial in situ-produced cosmogenic nuclides, with the most commonly measured being 10Be and 26A1 in quartz. To extract and then separate these radionuclides from quartz and prepare them in the oxide form suitable for accelerator mass spectrometry (AMS) requires extensive and careful laboratory processing. Here we discuss the suitability of a crushed, sieved and etched, sub-aerially exposed vein quartz specimen (CoQtz-N) to act as a reference material for chemical laboratory preparation and AMS measurements. Splits of CoQtz-N were distributed to eleven target preparation laboratories. The CoQtz-N 10Be targets were then measured at seven different AMS facilities and five of the preparation laboratories had their 26A1 targets measured at four different AMS facilities. We show that CoQtz-N splits are sufficiently homogeneous with regard to nuclide concentrations, that it has been cleaned of any atmospheric derived (i.e. meteoric) 10Be and that it has low concentrations of the major elements that can interfere with Be and A1 extraction chemistry and AMS measurements. We derive preliminary concentrations for 10Be and 26Al in CoQtz-N as 2.53 ± 0.09 × 106 at/g and 15.6 ± 1.6 × 106 at/g, respectively, at the 95% confidence limit. © 2019 Elsevier B.V.
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    Quantifying soil loss with in-situ cosmogenic 10Be and 14C depth-profiles
    (Elsevier, 2015-04-01) Fülöp, RH; Bishop, P; Fabel, D; Cook, GT; Everest, J; Schnabel, C; Codilean, AT; Xu, S
    Conventional methods for the determination of past soil erosion provide only average rates of erosion of the sediment's source areas and are unable to determine the rate of at-a-site soil loss. In this study,we report insitu produced cosmogenic 10Be, and 14C measurements from erratic boulders and two depth-profiles from Younger Dryas moraines in Scotland, and assess the extent to which these data allow the quantification of the amount and timing of site-specific Holocene soil erosion at these sites. The study focuses on two sites located on end moraines of the Loch Lomond Readvance LLR):Wester Cameron and Inchie Farm, both near Glasgow. The site nearWesterCameron does not showany visible signs of soil disturbance andwas selected in order to test (i) whether a cosmogenic nuclide depth profile in a sediment body of Holocene age can be reconstructed, and (ii) whether in situ 10Be and 14C yield concordant results. Field evidence suggests that the site at Inchie Farm has undergone soil erosion and this site was selected to explore whether the technique can be applied to determine the broad timing of soil loss. The results of the cosmogenic 10Be and 14C analyses atWester Cameron confirm that the cosmogenic nuclide depth-profile to be expected from a sediment body of Holocene age can be reconstructed. Moreover, the agreement between the total cosmogenic 10Be inventories in the erratics and the Wester Cameron soil/till samples indicate that there has been no erosion at the sample site since the deposition of the till/moraine. Further, the Wester Cameron depth profiles show minimal signs of homogenisation, as a result of bioturbation, and minimal cosmogenic nuclide inheritance from previous exposure periods. The results of the cosmogenic 10Be and 14C analyses at Inchie Farm show a clear departure from the zero-erosion cosmogenic nuclide depth profiles, suggesting that the soil/till at this site has undergone erosion since its stabilisation. The LLR moraine at the Inchie Farm site is characterised by the presence of a sharp break in slope, suggesting that the missing soilmaterialwas removed instantaneously by an erosion event rather than slowly by continuous erosion. The results of numerical simulations carried out to constrain the magnitude and timing of this erosion event suggest that the eventwas relatively recent and relatively shallow, resulting in the removal of circa 20e50 cm of soil at a maximum of ~2000 years BP. Our analyses also show that the predicted magnitude and timing of the Inchie Farm erosion event are highly sensitive to the assumptions that are made about the background rate of continuous soil erosion at the site, the stabilisation age of the till, and the density of the sedimentary deposit. All three parameters can be independently determined a priori and so do not impede future applications to other localities. The results of the sensitivity analyses further show that the predicted erosion event magnitude and timing is very sensitive to the 14C production rate used and to assumptions about the contribution of muons to the total production rate of this nuclide. Thus, advances in this regard need to be made for the method presented in this study to be applicablewith confidence to scenarios similar to the one presented here. © 2015, Elsevier B.V.
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    Slow, patchy landscape evolution in northern Sweden despite repeated ice sheet glaciation
    (Geological Society of America, 2006-01-01) Stroeven, AP; Harbor, J; Fabel, D; Kleman, J; Hättestrand, C; Elmore, D; Fink, D; Fredin, O
    The conventional assumption that erosion by ice sheets is pervasive and effective in landscape evolution is tested in northern Sweden using geomorphic mapping and cosmogenic nuclide analyses of formerly glaciated surfaces. The following evidence indicates that recent glaciations in this region have produced only slow and patchy landscape evolution: (1) Geomorphic mapping shows that at least 20% of the repeatedly glaciated study region in the northern Swedish mountains has landforms that are relict, i.e., clearly nonglacial in origin. (2) The contrast between cosmogenic apparent exposure ages from relict landforms in the northern Swedish mountains and from overlying glacial erratics and juxtaposed glacially eroded bedrock surfaces, which are consistent with last deglaciation, implies that the relict landforms have been preserved through multiple glacial cycles. (3) Apparent 10Be and 26Al exposure ages for tor summit bedrock surfaces in the northern Swedish lowlands reveal that these relict landforms have survived at least eleven exposure and ten burial events with little or no erosion over the past ∼1 m.y. (4) The northern Swedish lowland and mountains are primarily covered by glacial landforms. However geomorphic mapping suggests that even these landforms may have undergone limited erosion during the last glacial cycle. Cosmogenic 10Be and 36Cl data from what appear to be heavily scoured areas in one glacial corridor indicate erosion of only ∼2 ± 0.4 m of bedrock during the last glaciation. These results suggest that in some areas the overall modification produced by ice sheets may be more restricted than previously thought, or it has occurred preferentially during earlier Quaternary glacial periods. © 2020 GeoScienceWorld