Last deglaciation in the central Balkan Peninsula: Geochronological evidence from the Jablanica Mt. (North Macedonia)
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Abstract:
Several studies applied numerical age determination methods to examine glacial phases of the central Balkan Peninsula. However, the resulting datasets are contradictory, meaning that further discussion is needed. This study provides 10Be cosmic ray exposure (CRE) ages of a succession of glacial landforms in the Jablanica Mt. (North Macedonia), aiming at a better understanding of Late Pleistocene glacier development in the area. On the basis of the mapped glacial landforms, six glacial stages were identified and their mean equilibrium line altitudes (ELAs) were estimated. The CRE ages of five glacial stages - from the second oldest to the youngest - were determined between 16.8+0.8/−0.5 ka and 13.0+0.4/−0.9 ka. Accordingly, the most extensive glaciation in the Jablanica Mt. occurred before ~17 ka. The average ELA of the glaciers was 1792 ± 18 m a.s.l. during the largest ice extent, and 2096 ± 18 m during the last phase of the deglaciation. Independent reconstructions of key climatic drivers of glaciological mass balance suggest that glacial re-advances during the deglaciation were associated to cool summer temperatures before ~15 ka. The last glacial stillstand apparently resulted from a modest drop in summer temperature coupled with increased winter snow accumulation. In the study area no geomorphological evidence for glacier advance after ~13+0.4/−0.9 ka could be found. On the basis of independent climate proxies we propose that the last glacier advance occurred no later than ~13 ka, and glaciers were withdrawing during the Younger Dryas when low temperatures were combined with dry winters.Keywords:
Deglaciation
Glacial landform
Surface exposure dating
Last Glacial Maximum
Deglaciation
Stadial
Last Glacial Maximum
Surface exposure dating
Landform
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Landform
Glacial landform
Terminal moraine
Surface exposure dating
Mountain range (options)
Last Glacial Maximum
Bedrock
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Surface exposure–age dating was applied to rock surfaces associated with ice‐marginal moraines at elevations of ~1520–1780 m a.s.l. on the slopes of Galdhøpiggen and Glittertinden, the two highest mountains in Scandinavia located in the Jotunheimen mountains of central southern Norway. This is important for understanding the pattern and timing of wastage of the Scandinavian Ice Sheet at the Younger Dryas–Holocene transition. Cosmogenic exposure dating (here 10 Be dating) of boulders from the moraine ridges yielded overall mean ages (corrected for glacio‐isostatic uplift, surface erosion and snow shielding) of ~11.6 ka from Galdhøpiggen and ~11.2 ka from Glittertinden. Similar 10 Be ages were also obtained from additionally collected proximal and distal erratic boulders and bedrock samples. These enabled age calibration of Schmidt‐hammer R ‐values and independent Schmidt‐hammer exposure‐age dating (SHD) of the moraine ridges, which yielded comparable mean SHD ages of ~10.8 and ~10.6 ka from the Galdhøpiggen and Glittertinden sites, respectively. Taking account of the age resolution and other limitations of both dating techniques, the results suggest that the two sets of moraines have approximately the same age but that neither technique can distinguish unambiguously between moraine formation in the late Younger Dryas or Early Holocene. Together with features of moraine‐ridge morphology and estimates of equilibrium‐line altitude depression of ~360–575 m (corrected for land uplift), the results imply moraine formation during short‐lived re‐advances of active glaciers, at least the lower reaches of which were warm‐based. It is concluded that the local glaciers remained active and advanced during deglaciation either very late in the Younger Dryas or very early in the Holocene, possibly in response to the Preboreal Oscillation at ~11.4 ka. The study supports the concept of a thin Younger Dryas ice sheet and places time constraints on the timing of final deglaciation in southern Norway.
Surface exposure dating
Deglaciation
Allerød oscillation
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Four boulder samples from the Piano del Praiet frontal moraine in the Gesso della Barra Valley (Maritime Alps) have been 10 Be dated. The results give a weighted mean age of 11 340±370 (870) yr, constraining the frontal moraine to the Egesen glacial stadial, during the Younger Dryas cold phase. By applying the same 10 Be production rate to other Egesen moraines previously dated in the Alps, we obtain similar ages for all of them. This suggests a synchroneity of the Egesen deglaciation in the European Alps at the end of the Younger Dryas. From the palaeoshape of the Egesen glacier, reconstructed by means of geomorphological mapping, an Equilibrium Line Altitude depression (δELA) of −520 to −530 m, with respect to the present‐day ELA, and of −260 to −320 m, with respect to the Little Ice Age ELA, has been calculated. Comparison with other Alpine sector δELAs indicates that the Maritime Alps experienced humid climatic conditions during the Younger Dryas.
Deglaciation
Allerød oscillation
Stadial
Surface exposure dating
Terminal moraine
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We measured 10 Be concentrations in boulders collected from the Orsha and Braslav moraines, associated with the Last Glacial Maximum extent and a recessional stage of the Scandinavian Ice Sheet (SIS), respectively, providing a direct dating of the southeastern sector of the ice‐sheet margin in Belarus. By combining these data with selected existing radiocarbon ages, we developed a chronology for the last deglaciation of Belarus. The northeastern part of the country remained ice free until at least 19.2 ± 0.2 cal. kyr BP, whereas the northwestern part of the country was ice free until 22.3 ± 1.5 cal. kyr BP. A lobate ice margin subsequently advanced to its maximum extent and deposited the Orsha Moraine. The ice margin retreated from this moraine at 17.7 ± 2.0 10 Be kyr to a position in the northern part of the country, where it deposited the Braslav Moraine. Subsequent ice‐margin retreat from that moraine at 13.1 ± 0.5 10 Be kyr represented the final deglaciation of Belarus. Direct dating of these moraines better constrains the relation of ice‐margin positions in Belarus to those in adjacent countries as well as the SIS response to climate change.
Deglaciation
Surface exposure dating
Last Glacial Maximum
Margin (machine learning)
Chronology
Terminal moraine
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Abstract We present 10 in situ cosmogenic exposure ages from two moraines on the Isle of Skye. The Strollamus medial moraine was deposited during deglaciation of the Devensian ice sheet and yields a mean exposure age from five samples of 14.3 ± 0.9 ka. The moraine age indicates that a significant ice mass existed on Skye at the time of a regional readvance recorded in Wester Ross, northwest Scotland. Taken at face value the ages suggest that deglaciation did not occur until well into Greenland Interstade 1. The Slapin moraine represents the local limit of the Loch Lomond Readvance (LLR) and yields a mean exposure age from five samples of 11.5 ± 0.7 ka, which is consistent with deposition relating to the LLR. These ages suggest that the maximum extent may have been reached late in the stadial and that some glaciers may have remained active until after the climatic amelioration that marks its end. This scenario is considered unlikely given the nature of the climate during this period, which leads us to call for a locally calibrated production rate. Copyright © 2011 John Wiley & Sons, Ltd.
Deglaciation
Stadial
Surface exposure dating
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Deglaciation
Meltwater
Outwash plain
Glacial landform
Landform
Stadial
Terminal moraine
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Deglaciation
Surface exposure dating
Cosmogenic nuclide
Stadial
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We measured 10Be concentrations in boulders collected from the Orsha and Braslav moraines, associated with the Last Glacial Maximum extent and a recessional stage of the Scandinavian Ice Sheet (SIS), respectively, providing a direct dating of the southeastern sector of the ice-sheet margin in Belarus. By combining these data with selected existing radiocarbon ages, we developed a chronology for the last deglaciation of Belarus. The northeastern part of the country remained ice free until at least 19.2 ± 0.2 cal. kyr BP, whereas the northwestern part of the country was ice free until 22.3 ± 1.5 cal. kyr BP. A lobate ice margin subsequently advanced to its maximum extent and deposited the Orsha Moraine. The ice margin retreated from this moraine at 17.7 ± 2.0 10Be kyr to a position in the northern part of the country, where it deposited the Braslav Moraine. Subsequent ice-margin retreat from that moraine at 13.1 ± 0.5 10Be kyr represented the final deglaciation of Belarus. Direct dating of these moraines better constrains the relation of ice-margin positions in Belarus to those in adjacent countries as well as the SIS response to climate change.
Deglaciation
Surface exposure dating
Last Glacial Maximum
Margin (machine learning)
Chronology
Terminal moraine
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Abstract 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 10 Be and 26 Al 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 10 Be and 26 Al 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.
Deglaciation
Cosmogenic nuclide
Surface exposure dating
Last Glacial Maximum
Terminal moraine
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