Glacio-isostatic Depression Research Articles

Early and Middle Pleistocene glaciation of the southern Patagonian plain

Evidence of at least three Early to Middle Pleistocene glaciations is recorded in the stratigraphic exposures near the outer limit of glaciation in southern Patagonia. At Cabo Vírgenes, at the mouth of the Strait of Magellan, up to 70 m of till, gravel, sand, and stony silt were deposited in a grounding-line environment at the front of the Magellan lobe along a front several tens of kilometres wide. Accommodation space for the sediments was produced by glacio-isostatic depression resulting from the advance of the Magellan lobe to the Atlantic coast. At that time, the ‘moat’ in which the sediments accumulated may have been seaward of the modern Atlantic shoreline because the continental shelf is shallow and sea level was much lower than it is today. The sediments at Cabo Vírgenes are normally magnetized, carry no reversed overprints, and thus probably date to the Brunhes Chron (<0.774 Ma). Seacliff exposures south of the Strait of Magellan along the Atlantic coast of northern Tierra de Fuego expose two tills separated by glaciofluvial sediments. Although not dated, the tills record two advances of the Magellan lobe onto the Atlantic continental shelf. The location of the exposures relative to Cabo Vírgenes indicates that the upper of the two tills may correlate with the Cabo Vírgenes drift. The Tres de Enero highway cut, 90 km northwest of Cabo Vírgenes, exposes lodgement tills deposited during the Great Patagonian glaciation (GPG) – two stacked, normally magnetized tills overlie a reversely magnetized till. Truncated sand wedges separate each of the three tills, indicating that the tills record three separate Early to Middle Pleistocene glaciations. The younger of the two normally magnetized tills, and perhaps both, were deposited in the Brunhes Chron; the lowest, reversely magnetized till records extensive glaciation late during the Matuyama Chron (2.608–0.780 Ma). At Bella Vista in the Río Gallegos valley, a 0.89-Ma-old basalt flow caps a thick unit of normally magnetized glaciofluvial gravel, which was probably deposited during the Jaramillo Subchron (1.075–0.991 Ma), but certainly not later. Sediments at Tres de Enero and Bella Vista show that the GPG is not a single event as originally thought, but rather at least three glaciations, perhaps spanning several hundred thousand years.

Advance and retreat of the marine-terminating Irish Sea Ice Stream into the Celtic Sea during the Last Glacial: Timing and maximum extent

The dynamics of the British-Irish Ice Sheet (BIIS) during the Last Glacial were conditioned by marine-based ice streams, the largest of which by far was the Irish Sea Ice Stream (ISIS) which drained southwest across the Celtic shelf. The maximum extent and timing of the ISIS have been constrained by onshore evidence from the UK and Ireland, and by glacigenic sediments encountered in a small suite of vibrocores from the UK-Irish continental shelf, from which a single radiocarbon date is available. These data have long supported ice advance to at least the mid-shelf, while recent results suggest the ISIS may have extended 150 km farther seaward to the shelf edge. The glacigenic sequences have not been placed within a secure seismic-stratigraphic context and the relationship between glaciation and the linear sediment megaridges observed on the outer shelf of the Celtic Sea has remained uncertain. Here we report results of sedimentological, geochemical, geochronological and micropalaeontological analyses combined with a seismic-stratigraphic investigation of the glacigenic sequences of the Celtic Sea with the aims of establishing maximum extent, depositional context, timing and retreat chronology of ISIS. Eight lithofacies packages are identified, six of which correlate with seismic facies. Lithofacies LF1 and LF2 correlate to a seafloor seismic facies (SF1) that we interpret to record the postglacial and Holocene transgressive flooding of the shelf. Lithofacies LF10 (till), LF3, LF4 and LF8 (glacimarine) correlate to different seismic facies that we interpret to be of glacigenic origin based on sedimentological, geotechnical and micropalaeontological evidence, and their distribution, supported by geochemical evidence from lithofacies LF8 and LF10 indicate extension of ISIS as far as the Celtic Sea shelf break. New radiocarbon ages on calcareous micro- and macrofauna constrain this advance to be between 24 and 27 cal ka BP, consistent with pre-existing geochronological constraints. Glacimarine lithofacies LF8 is in places glacitectonically contorted and deformed, indicating ice readvance, but the nature and timing of this readvance is unclear. Retreat out of the Celtic Sea was initially rapid and may have been triggered by high relative sea-levels driven by significant glacio-isostatic depression, consistent with greater ice loads over Britain and Ireland than previously considered.

Early deglaciation of the British-Irish Ice Sheet on the Atlantic shelf northwest of Ireland driven by glacioisostatic depression and high relative sea level

Understanding the triggers and pace of marine-based ice sheet decay is critical for constraining the future mass loss and dynamic behaviour of marine-based sectors of the large polar ice sheets in Greenland and Antarctica. Numerical models which seek to predict this behaviour need to be calibrated against data from both contemporary and palaeo-ice sheets, and the latter requires accurate reconstruction of former ice sheet extent, dynamics and timing. Marine geophysics, sediment cores, benthic foraminiferal assemblages and radiocarbon dating are used to reconstruct the extent of the last British-Irish Ice Sheet (BIIS), and the timing and style of its retreat on the Atlantic shelf northwest of Ireland. Shelf edge moraines and subglacial till recovered in cores from the outer continental shelf are dated to younger than 26.3 ka cal BP and indicate an extensive ice sheet at the Last Glacial Maximum (LGM) that was grounded to the shelf edge. Nested arcuate moraines record the subsequent episodic retreat of the ice sheet across the shelf. Lithofacies and associated foraminiferal assemblages demonstrate that this retreat occurred in a glacimarine environment as a grounded tidewater margin and that high relative sea level and cold waters prevailed during retreat. Radiocarbon dates indicate that the timing of initial ice sheet retreat from the shelf edge occurred in the interval between 26.3 and 24.8 ka cal BP, during the period of minimum global eustatic sea level, and that the ice sheet had retreated to the mid-shelf by 24.8 ka cal BP. The ‘Donegal Bay Moraine’, a large moraine at the mouth of Donegal Bay, records a major stillstand and readvance of the ice sheet during deglaciation between 20.2 and 17.9 ka cal BP. Estimated retreat rates of 5.5–35 m a−1 across the shelf demonstrate that retreat was slow. It is noteworthy that retreat was initiated in the absence of ocean warming and when eustatic sea level was at a minimum. The sea-level rise that initiated deglaciation from the shelf edge therefore, is inferred to have been a product of local glacio-isostatic crustal depression rather than external forcing. This demonstrates that marine-based sectors of ice sheets can trigger their own demise internally through glacio-isostatic adjustment and it provides an explanation for the early retreat of the BIIS on the Atlantic shelf during the global LGM (gLGM).

Relative sea-level changes and glacio-isostatic adjustment on the Magdalen Islands archipelago (Atlantic Canada) from MIS 5 to the late Holocene

The Magdalen Islands (Québec, Canada) in the centre of the Gulf of St. Lawrence are located in a strategic position for providing an overview of the relative sea-level (RSL) history of the Maritime Provinces of eastern Canada. Although data are available for the coastal terrestrial areas of the Maritimes, data from the Gulf are very scarce and both the RSL and glacio-isostatic adjustment (GIA) models extrapolate for this central region. This study provides new stratigraphic and chronological data from four outcrops and two coring sites on the Magdalen Islands. In addition to the five samples used mainly for age control purposes, nine new luminescence ages are presented. With these new data added to the available literature, a new RSL curve is reconstructed for the LGM to the late Holocene period and a partial curve is proposed for the interval between the late MIS 4 to the MIS 3. Data also indicate a few insights for the MIS 5 period. Results reveal that for the LGM to the late Holocene, the curve corresponds to the J-shaped curve scenario recognized in the literature. The RSL changes during this period are the result of glacio-isostatic rebound, migration and collapse of the peripheral forebulge, and eustatic sea-level changes. For the LGM to the early Holocene, glacio-isostatic depression curves displaying a few local differences are also proposed. For the late Holocene, the data constrain the curve between two types of indicators, i.e. marine and terrestrial, and indicate that the RSL has risen at least 3 m during the last two millennia. Sediments dated to the MIS 5 and the interval between the late MIS 4 and the MIS 3 illustrate that the GIA following the LGM also occurred for the MIS 5 interglacial and the MIS 3 interstadial. Finally, recent GIA models are discussed in light of the results of this paper.

Late glacial to early Holocene development of southern Kattegat

The Kattegat region is located in the wrench zone between the Fennoscandian shield and the Danish Basin that has repeatedly been tectonically active. The latest ice advances during the Quaternary in the southern part of Kattegat were from the north-east, east and south-east (Larsen et al. 2009). The last deglaciation took place at c. 18 to 17 ka BP (Lagerlund &amp; Houmark-Nielsen 1993; Houmark-Nielsen et al. 2012) and was followed by inundation of the sea that formed a palaeo-Kattegat (Conradsen 1995) with a sea level that was relatively high because of glacio-isostatic depression. Around 17 ka BP, the ice margin retreated to the Øresund region and meltwater from the retreating ice drained into Kattegat. Over the next millennia, the region was characterised by regression because the isostatic rebound of the crust surpassed the ongoing eustatic sea-level rise, and a regional lowstand followed at the late glacial to Holocene transition (Mörner 1969; Thiede 1987; Lagerlund &amp; Houmark-Nielsen 1993; Jensen et al. 2002a, b).

Holocene sea levels, Last Glacial Maximum glaciomarine environments and geophysical models in the northern Irish Sea Basin, UK

Newly acquired geological records from the Isle of Man reveal intercalated intertidal and terrestrial sediments that record a relative sea-level rise from ca. − 3.86 m in the early Holocene up to a mid-Holocene maximum between ca. 6.6 and 4.5 cal kyr BP at ca. + 2.25 m. When compared with similar marine records from elsewhere in the northern Irish Sea Basin, the sea-level data confirm a strong north–south trend in glacioisostatic loading, but little east to west difference in loading. This pattern results from the central northern sectors of the British ice sheet over Scotland strongly influencing the glacioisostatic downwarping throughout the northern Irish Sea Basin. Differential ice thicknesses over the Irish Sea, the Lake District and Ireland did not cause perturbations of local glacioisostatic signatures. The Holocene marine data in the central Irish Sea record a slow termination of global eustatic sea-level rise during the early Holocene. Geophysical predictions of relative sea level, partially constrained by the Holocene RSL observations but extrapolated to the Last Glacial Maximum, show the potential for shallow marine conditions in the central Irish Sea Basin and in northeast Ireland between ca. 21.0–16.0 cal kyr BP. However, glaciomarine deposits in northeast Ireland suggest the model relative sea-level predictions are too low, and require increased ice loading or a thinner lithosphere to generate extra glacioisostatic depression at the time of deglaciation. Furthermore, predicted deglacial relative sea level for northeast Ireland does not match the geological record, highlighting complex ice margin/ocean interaction during deglaciation. On the Isle of Man, where glacioisostatic loading is of a similar magnitude to that across northeast Ireland, the presence of grounded ice inhibited marine incursion during early deglaciation, but the occurrence of glaciolacustrine conditions along the ice margin as it moved northwards supports model predictions that relative sea-level fell below present during the Late Glacial/early Holocene due to rapid glacioisostatic rebound.

Early growth of the last Cordilleran ice sheet deduced from glacio-isostatic depression in southwest British Columbia, Canada

Relative sea level at Vancouver, British Columbia rose from below the present datum about 30,000 cal yr B.P. to at least 18 m above sea level 28,000 cal yr B.P. In contrast, eustatic sea level in this interval was at least 85 m lower than at present. The difference in the local and eustatic sea-level positions is attributed to glacio-isostatic depression of the crust in the expanding forefield of the Cordilleran ice sheet during the initial phase of the Fraser Glaciation. Our findings suggest that about 1 km of ice was present in the northern Strait of Georgia 28,000 cal yr B.P., early during the Fraser Glaciation.

Rapid and rhythmic ice sheet fluctuations in western Scandinavia 15-40 Kya–a review

The onshore record of Middle to Late Weichselian sediments and glacial history in Norway indicates a succession of four major ice advances alternating with rapid, considerable ice recessions and interstadial conditions. During all the glacial advances the ice sheet expanded from onshore/inland positions to the shelf areas. The basis for visualizing these variations in glaciation curves constructed along nine transects from inland to shelf, and for interpretation of the palaeoclimatic history, is the regional Quaternary stratigraphy, more than 300 datings, fossil content and some palaeomagnetic data. The methods applied in recent years for AMS radiocarbon dating of glacial sediments with low organic carbon content have given promising results with respect to accuracy and precision, and the results of such datings were an important tool for our reconstructions and for timing of the ice oscillations. The rapid and rhythmic ice fluctuations, as reconstructed in our new model, have been fairly synchronous in most parts of Norway. Ice advances commenced and culminated at 40, 30-28, 24-21 and 18-15 (14C) Kya. We describe three intervening interstadials from inland sites: Hattfjelldal I, Hattfjelldal II and Trofors. Our stratigraphical record also includes many indications of high, pre-Holocene, relative sea levels, suggesting a considerable glacioisostatic depression of western Scandinavia during the interstadials. In our glaciation model we suggest that, in addition to precipitation, the mountainous fjord and valley topography, glacial isostasy and relative sea level changes were probably more important for the size of the glacial fluctuations than were air temperature changes.

The extent of the Late Weichselian ice sheet in the southeastern Barents Sea

We have compiled a large number of seismic records and descriptions of sediment cores obtained from the southeastern Barents Sea (Pechora Sea) by former Soviet Union institutions. Five major seismostratigraphic units (SSU-I–V) were recognized. The oldest till (SSU-V) is mainly confined to the southernmost area and is covered by a 100–150-m-thick wedge of Middle Weichselian marine sediments (SSU-IV) distal to the mouth of the Pechora River. Three Late Weichselian ice sheet margins are identified on the Pechora Sea shelf. The oldest is named the Kolguev Line and it marks the southern limit of the youngest till sheet (SSU-III) in the Barents Sea as well as the northern, erosional limit of SSU-IV and -V. The Kolguev Line marks the maximum extension of the Barents Ice Sheet during the Late Weichselian. The Kurentsovo Line, which is located 50–100 km further to the north, is much more expressed than the Kolguev Line and corresponds with long ice-pushed bedrock ridges and till ridges. Up to 100-m-thick accumulations of glaciomarine sediments (SSU-II) were mapped on the southern side of the Kolguev Line whereas less than 10–20 m where found on the northern side of the inferred ice sheet margin, indicating that the ice front remained at this position for considerable time. The youngest line is the southern continuation of the Admiralty Banks moraines, which have previously been mapped along the western margin of Novaya Zemlya. The Kolguev and Kurentsovo lines were both formed by an ice sheet centered in the Barents Sea, whereas the Admiralty Banks moraines were deposited from an ice sheet over Novaya Zemlya during the final stage of the Late Weichselian, possibly during the Younger Dryas. Submerged shorelines of Late Weichselian/Early Holocene ages have been identified on the shelf down to a water depth of 50–70 m indicating a modest glacio-isostatic depression that partly compensated the sea-level fall during the last glacial maximum.

A critical review of the glaciomarine model for Irish sea deglaciation: evidence from southern Britain, the Celtic shelf and adjacent continental slope

AbstractIn support of their ‘glaciomarine’ model for the deglaciation of the Irish Sea basin, Eyles and McCabe cited the occurrence of distal glaciomarine mud drapes onshore in the Isles of Scilly and North Devon, and of arctic beach‐face gravels and sands around the shores of the Celtic Sea. Glacial and sea‐level data from the southern part of the Irish Sea in the terminal zone of the ice stream and the adjacent continental slope are reviewed here to test this aspect of the model. The suggestion that the glacial sequences of both the Isles of Scilly and Fremington in North Devon are glaciomarine mud drapes is rejected. An actively calving tidewater margin only occurred early in the deglacial sequence close to the terminal zone in the south‐central Celtic Sea. Relative sea‐levels were lower, and therefore glacio‐isostatic depression less, than envisaged in the glaciomarine model. Geochronological, sedimentological and biostratigraphical data indicate that the raised beach sequences around the shores of the Celtic Sea and English Channel were deposited at, or during regression soon after, interglacial eustatic highstands. Evidence for ice‐rafting at a time of high relative sea‐levels is restricted to a phase(s) earlier than the Late Devensian. These data indicate that the raised beach sequences have no bearing on the style of Irish Sea deglaciation. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Middle Pleistocene raised beach anomalies in the English Channel: regional and global stratigraphic implications

Palaeo-shore positions help to evidence long-term eustatic changes and assist in the understanding of tectonic movements at a regional scale. Raised beaches anomalies exist in the Channel region and may result from deformations induced by neotectonic or by glacio-isostasy. The aim of this paper is to re-analyse, within their geodynamic context in the Channel and Dover Strait regions, the stratigraphy and the datings of palaeo-shores of Middle and Upper Pleistocene ages. This sector of Europe is characterised by strong geological contrasts and is controlled by two main geological boundaries: in the north, the Variscan Overthrust (corresponding approximately to the position of the Dover Strait) and, in the south, the Northern Branch of the Southern Brittany shearing zone. These two boundaries border a domain which seems to behave rather homogeneously on a large scale under the control of plate tectonics. Today, shorelines are subsiding north and south of this ‘Channel’ region. Episodic uplift largely controlled the open or closed status of the Dover Strait, especially after the Messinian and Early Quaternary, by reactivating Variscan structures. After 400 ka, global cooling allowed supplementary deformations in the area to be induced by glacio-isostatic rebound and clustered seismic activity during the phase of ice sheet building. Evidence of eight different transgressions dated by ESR from Oxygen Isotopic Stage (OIS) 13 to the end of OIS 5 shows the complexity of the sea-level records in a region unstable for isostatic and neotectonic reasons. Due to glacio-isostatic depression, transgressions are possible in late glacial times as well as during full interglacials. Most platforms were initially cut, during the Late Miocene, and seem to have been re-trimmed several times, especially by shore ice rafting since OIS 9. Regionally, the sea apparently rose to about the same level in O.I. Stages 11, 9 and 7. Glacio-isostatic and glacio-eustatic relative displacements of the sea level together with background tectonic movements have modified coastal positions and have temporarily altered the intensity of tidal currents. The oldest shoreline deposits are preserved only in subsiding areas, controlled by the deep crustal pattern. Neotectonics related to Variscan structure reactivation still dominates glacio-isostatic deformation and basin subsidence. The OIS 7 positive anomaly seems related to a regional relaxation event.

Late glacial drainage systems along the northwestern margin of the Laurentide Ice Sheet

The evolution of drainage systems along the retreating northwestern Laurentide Ice Sheet was complex. The interaction of ice-margin configuration, topography and glacioisostasy resulted in a network of meltwater rivers that variably overflowed to the Arctic and Pacific Oceans and to the Gulf of Mexico. Glacial lakes also changed dramatically in size and location during the period of deglaciation. At the last (and all time) glacial maximum, the ice sheet extended into the eastern Cordillera, blocking northward and eastward drainage to the Arctic Ocean. Some meltwater and most non-glacial runoff were diverted through the mountains to the Yukon River basin, into Alaska and the Pacific Ocean. Retreat from the glacial maximum prior to 21 ka BP allowed proglacial drainage from the western margin of the ice sheet to flow into the Beaufort Sea/Arctic Ocean. Deglaciation was rapid after about 13 ka BP, with the present route of the lower Mackenzie River established between 13 and 11.5 ka BP. Continued ice retreat led to significant southward expansion of the Mackenzie/Beaufort drainage basin at about 11.5 ka BP through drainage capture of glacial Lake Peace, which previously had drained southeastward into the Missouri River and to the Gulf of Mexico. Very rapid ice retreat between 10.5 and 10 ka BP allowed glacial lake McConnell to expand down-slope in contact with the ice margin.Numerous glacial lakes occurred along the northwestern margin of the ice sheet during the maximum and retreat phases. These include ice-dammed glacial Lake Old Crow, which occupied unglaciated terrain of the northern Yukon, and glacial Lake Peace, which utilized a number of outlets as it migrated eastward with the ice front along the Peace Valley. The largest glacial lakes in the region were the result of glacioisostatic depression reversing the regional drainage. The Mackenzie Phase of glacial Lake McConnell was the second largest Pleistocene lake in North America (> 215,000 km2). Late glacial and post-glacial changes in drainage systems were largely in response to isostatic rebound.

Carboniferous glaciation in Gondwana. Evidence for grounded marine ice and continental glaciation in southwestern Argentina

Upper Paleozoic sedimentary rocks in western Argentina accumulated in retro-arc foreland basins in the Gondwana continental margin. A glacial component in these rocks was recognized early in this century but reconstructions of the nature of the glaciation differ markedly. The dominant proposal sustains that glaciation in this region was of alpine-type, with glaciers descending from mountain ranges both inland and along the edge of the continent, and that the numerous intercalated diamictites were mostly deposited as subaquatic debris flows only indirectly connected with the presence of glacier ice. A stratigraphic and sedimentologic study of Middle Carboniferous glacigenic deposits of the Tepuel Group in central western Patagonia, southwestern Argentina, shows that two major diamictite facies are present: (a) massive diamictite, the more abundant, forms regionally extensive and thick (<60 m) pebbly bodies with boundaries transitional to non-glacial open shelf deposits; these are interpreted as rain-out till; and (b) chaotic diamictite, yielding thin (< 10 m) laterally discontinuous bouldery bodies showing erosive bases, strong substratal deformation, and upward transition to massive diamictite; these are interpreted as subglacial till. A third type of glacial deposit consists of interbedded current-deposited and wave-worked conglomerates and sandstones, in strata that downlap onto non-glacial shelf mudstones; these are interpreted as submarine outwash fan deposits. The position of subglacial till and outwash fans relative to the paleoshoreline indicate deep regional incursions of grounded ice onto the shelf. In addition, deepening of the shelf coincident with initial glacial marine sedimentation in the early Middle Carboniferous, at a time of global lowstand, argues for glacio-isostatic depression of the shelf and suggests a considerable ice thickness. Paleotopographic considerations indicate that the centres of ice dispersal were located on moderately high intracratonic highlands. A regional erosion surface across these highlands is attributed to subglacial scour under a Patagonian ice cap that expanded onto the adjacent shelf during glacial maxima. Published information concerning ice distribution in Middle Carboniferous Gondwana supports the existence of an ice cover similar in lateral extent to that in modern Antarctica. The Patagonian ice cap would have been peripheral to this continental-sized ice mass.

Sedimentation in an ice-contact subaqueous setting: The mid-Pleistocene ‘North Sea Drifts’ of Norfolk, U.K.

In East Anglia, the mid-Pleistocene ‘North Sea Drifts’ extend over some 1500 km 2 of the coastal zone of North Norfolk. They are the oldest Pleistocene glacial sequences exposed in Britain, deposited during the Anglian Glaciation (ca. 450 ka BP?). Laminated and stratified pebbly mud (diamict) facies of the North Sea Drifts are widely regarded as the product of subglacial deposition below a terrestrial ice margin. In this paper these facies are identified as the product of subaqueous deposition in front of the margin of an ice sheet terminating in a large water body. Laminated, stratified, and massive diamict facies were deposited by the ‘rain-out’ of fine-grained sediment from suspension and coarse debris from floating ice, combined with downslope sediment gravity flow. Intraformational folds are the product of episodic downslope slumping and identify a regional paleoslope to the east, away from a major ice marginal moraine ridge (The Cromer Ridge). Exposures at Cromer show bulldozed ice-contact subaqueous sediments and ice-thrust chalk rafts. A fall in water-level emplaced shelly shoreface sands and beach gravels which are loaded into the underlying diamicts as large pan-shaped ‘sag basins’ with diapiric structures at their margins. Comparable sedimentary sequences are exposed elsewhere around the southern North Sea Basin; a glaciomarine setting in response to glacio-isostatic depression around the Anglian ice sheet is suggested.

Lacustrine sedimentation in a proglacial environment, Caribou River Valley, Yukon, Canada

Proglacial Quaternary lacustrine sediments deposited along the Caribou River Valley, Yukon, Canada, formed in a lake impounded by glacial ice that was retreating downslope. Sedimentation in the lake was dominated by turbid sediment underflows generated from the upslope, previously deglaciated region. The base of the sedimentary succession indicates a gradual transition from sporadic low‐density distal flows to higher density proximal flows. Continued sediment accumulation resulted in the construction of a subaqueous clay and silt bank. Sedimentation was dominated by deposition of suspension load clay carried by subseasonal bottom countercurrents induced by katabatic winds. This sedimentation pattern prevailed until the subaqueous bank was disturbed by mass movement. Removal of the sediment bank increased the depth of the nearshore area sufficiently to allow turbid underflows to dominate sedimentation once more. The changing sedimentation patterns reflect events in the areas away from the ice front, rather than changes in the activity of the impounding glacier. Similar successions could be developed in other glacial lakes impounded by glaciers which moved up topographical slopes, either pre‐existing or generated by glacioisostatic depression.

The late Quaternary history of Hall Land, northwest Greenland: Reply

The last ice limit on Hall Land, northwest Greenland, is marked by the Newman and Petermann moraines, which were deposited 40–60 km beyond the present ice margins in Newman Bay and Petermann Fiord, respectively. These moraines flank the eastern and western coasts of Hall Land but do not extend into its intervening central plain. As a result of glacioisostatic depression at this time, a full glacial sea transgressed the entire central plain via a narrow estuary located between the Newman Moraine and the northern plateau of Hall Land. The limit of this full glacial sea is isostatically tilted from 116 m asl on the adjacent coast of Ellesmere Island to 150 m asl on the southwest extremity of the central plain, where it reaches its apex. Pervasive marine silts cover the central plain and laterally thicken towards the Newman and Petermann moraines. Because of the height of the full glacial sea, these moraines were deposited in a submarine environment and mark the grounded margins of ice shelves floating in Hal...

The late Quaternary history of Hall Land, northwest Greenland

The last ice limit on Hall Land, northwest Greenland, is marked by the Newman and Petermann moraines, which were deposited 40–60 km beyond the present ice margins in Newman Bay and Petermann Fiord, respectively. These moraines flank the eastern and western coasts of Hall Land but do not extend into its intervening central plain. As a result of glacioisostatic depression at this time, a full glacial sea transgressed the entire central plain via a narrow estuary located between the Newman Moraine and the northern plateau of Hall Land. The limit of this full glacial sea is isostatically tilted from 116 m asl on the adjacent coast of Ellesmere Island to 150 m asl on the southwest extremity of the central plain, where it reaches its apex. Pervasive marine silts cover the central plain and laterally thicken towards the Newman and Petermann moraines. Because of the height of the full glacial sea, these moraines were deposited in a submarine environment and mark the grounded margins of ice shelves floating in Hall Basin and Newman Bay.Twenty-seven samples of marine pelecypods from the proximal and distal sides of these moraines were 14C dated. Distal to the moraines the limit of the full glacial sea is dated by in situ shells that range from 8200 to &gt; 33 000 BP. During this interval relative sea level remained stable and the ice load was apparently in isostatic equilibrium. Initial emergence (unloading) throughout the full glacial sea (~8200 BP) coincides with the initial penetration of the sea inside the Newman Moraine dated at 7965 BP and inside the Petermann Moraine at 8280 and 8295 BP.This research concludes that (1) there was no Nares Strait ice ridge during the last glaciation, (2) ice retreat of only 40–60 km can cause 140–150 m of emergence, and (3) the deglaciation of northwest Greenland began at 8000 and not 10 000 BP. This research confirms that the relative sea-level curves from the adjacent coast of Ellesmere Island were isostatically dominated by the Greenland Ice Sheet.

The last glaciation of west-central Ellesmere Island, Arctic Archipelago, Canada

Locally abundant ice-marginal landforms lie in a 500 km long zone with a distal margin 10–60 km west of the margins of modern ice caps on central Ellesmere Island. Much of this drift belt, at the heads of the fiords, was deposited by the oscillating margin of a coalesced predecessor of the modern ice caps between 9000 and 7000 BP. The ice continued to retreat east of the present margin, and readvanced to its modern limit in a middle and late Holocene cooler climate. Unweathered but undated till and striations at the base of the drift suggest that the belt does not mark the western limit of central Ellesmere Island ice in the last glaciation. The limit lies an unknown distance downfiord; glaciers in the fiords may have floated. No reliable evidence was found for a complete ice cover of western Ellesmere Island and Eureka Sound in the last glaciation; nevertheless much of central and southern Ellesmere Island and Devon Island may have been glaciated by a regime that left few erosional or depositional landforms. Alternatively, emergence of an unglaciated Eureka Sound, underway by 9000 BP, may have followed combined peripheral glacioisostatic depression by encircling ice caps, whereas at the drift belt emergence was less and later, controlled only by central Ellesmere Island ice.

Glacial Traces on the Island of Hopen, Svalbard: A Correction

As part of a programme dealing with the extent of ice sheets in northern and arctic Europe during the latest (Weichsel, Wiirm, Wisconsin) glaciation the Department of Physical Geography, University of Stockholm, from 1957 until the early 1970's, undertook a series of expeditions and field trips to different parts of the Svalbard archipelago. A main result of these investigations was an isobase map demonstrating land-uplift during the last 6 500 years; the 6 500 BP reference date being chosen because of the abundance of datable raised strandlines formed at that time. The uplift area is centered east of Spitsbergen and southeast of Nordaustlandet, and is believed to represent rebound from glacio-isostatic depression caused by an extensive ice-sheet over Svalbard and adjoining parts of Barents Sea during Weichsel time (Schytt, Hoppe, Blake and Grosswald 1968, Hoppe 1971). The idea of a vast ice-sheet in the Arctic during the Weichsel time was not totally new when we first presented it in the late 1960's. However, earlier presentations were based on rather weak arguments, if any. Since our early publications, numerous papers have appeared dealing with the same subject and arriving at very different conclusions, both as to the extent of the glaciation and as to the time of its maximum. For these reasons a special programme of further study, with data sampling from both land and sea bottom, was included in the Swedish Arctic Expedition YMER-80, undertaken in the summer of 1980.