The role of glacio-isostasy in the formation of post-glacial river terraces in relation to the MIS 2 ice limit: evidence from northern England
David R. BridglandRob WestawayAndy J. HowardJames B. InnésAntony J. LongW. A. MitchellMark WhiteTom S. White
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River terraces
Aggradation
Terrace (agriculture)
Last Glacial Maximum
Wisconsin glaciation
Deglaciation
The neoglacial history of South Norway is illuminated through a lichenometric study of 14 ice-marginal zones of glaciers situated along a right angled line running north-south and west-east to cover a vast area. Maps of the marginal zones two lichen growth curves, the moraine dates and a frequency diagram are presented on a plate, PI. 1. If there are reference points to check the growth curves, lichenometry is found to be reliable to fix the time of deglaciation of the moraine ridges within a period of about three hundred years. A total of 101 moraine ridges were dated and the results show that their deglaciation time is concentrated around 1930, 1905, 1900, 1880, 1860, 1840, 1820 and 1800. The deglaciation of the outermost moraines is concentrated within the period 1780–1820.
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Abstract In this study we have obtained 17 cosmogenic exposure ages from three well‐developed moraine systems – Halland Coastal Moraines (HCM), Göteborg Moraine (GM) and Levene Moraine (LM) – which were formed during the last deglaciation in southwest Sweden by the Scandinavian Ice Sheet (SIS). The inferred ages of the inner HCM, GM and LM are 16.7 ± 1.6, 16.1 ± 1.4 and 13.6 ± 1.4 ka, respectively, which is slightly older than previous estimates of the deglaciation based on the minimum limiting radiocarbon ages and pollen stratigraphy. During this short interval from 16.7 ± 1.6 to 13.6 ± 1.4 ka a large part (100–125 km) of the marine‐based sector of the SIS in southwest Sweden was deglaciated, giving an average ice margin retreat between 20 to 50 m a −1 . The inception of the deglaciation pre‐dated the Bølling/Allerød warming, the rapid sea level rise at 14.6 cal. ka BP and the first inflow of warm Atlantic waters into Skagerrak. We suggest that ice retreat in southwest Sweden is mainly a dynamical response governed by the disintegration of the Norwegian Channel Ice Stream and not primarily driven by climatic changes. Copyright © 2011 John Wiley & Sons, Ltd.
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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.
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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.
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Abstract An area west of Lake Bolmen in southwestern Sweden was investigated by geomorphological, lithostratigraphical, and sedimento‐logical methods. Ice movement directions inferred from striae, end moraines, and drumlins indicate that the initial deglaciation of the western part of the area was towards the NE. This was probably followed by a readvance from the N and a final deglaciation towards the N. In the eastern part of the Bohnen area the deglaciation was continuous and the ice movement gradually changed from a direction from the NE to a direction from the N. Sedimentological investigations were made in two moraine ridges. These and other ridges are connected, together named the Unnaryd moraine and are interpreted to consist of ice slope colluvium and debris flows deposited proglacially. The Unnaryd moraine is the eastward continuation of a previously known end moraine called the Torup moraine. The combined Torup‐Unnaryd moraine marks the southern limit of the readvance from the N. It was also found that the Unnaryd‐Torup moraine postdates a geomorphological border‐line across southern Sweden with which it was previously correlated. Andersson, G., 1997: Glacial dynamics during the deglaciation of the Bolmen area, SW Sweden. GFF, Vol. 119 (Pt. 3, September), pp. 207–212. Stockholm. ISSN 1103–5897.
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The deglaciation history of Balsfjord, northern Norway, and post-glacial mass movement events were investigated. Radiocarbon dates indicate that the Balsfjord glacier retreated from the Tromsø–Lyngen moraines about 10.4 14C Ky BP. Between ca. 10.3 14C Ky BP and 9.9 14C Ky BP, deposition of a distinct end moraine–the Skjevelnes moraine–in the central part of Balsfjord occurred. The transition from glacimarine to open marine sedimentary environment took place before 9.6 14C Ky BP. Between ca. 9.5 14C Ky BP and 8.4 14C Ky BP, at least one local and three regional mass movement events occurred. After this period, no gravity flow activity is preserved in the cores. The high frequency of mass movements in the early post-glacial period is presumed to be due to fast sea level changes and/or tectonic activity induced by rapid isostatic uplift.
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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.
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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.
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