The deglaciation of southern Sweden 13,500-10,000 B.P.

Because of its well-developed ice-marginal zones, SW Sweden is an important reference area for the study of deglaciation, chronology and palaeoclimate 13,500-10,000 B.P. The ice-marginal zones are described and defined. Earlier research and opinions concerning the deglaciation are summarized. Based on radiocarbon dates from shells, vertebrate bones and limnic sediments, a revised deglaciation chronology is presented. This chronology is supported by biostratigraphic transects of time-space diagrams. The radiocarbon and varve chronologies are compared. Some ice-marginal zones are supposed to be 400 to 900 years older than expected from the varve chronology. The deglaciation chronology is correlated within the southern margin of the Scandinavian inland ice. Various consequences for the interpretation of glacial dynamics, shoreline displacement, and the biological environment are mentioned.     

The deglaciation of Finland after 10,000 B. P.

Various concepts of the deglaciation of Finland are presented in the form of a historical review. The suggestions of an early (12,000–10,000 B.P) deglaciation of eastern and northern Finland are considered to be erroneous. A map depicting the ice recession as successive ice-marginal lines is presented. According to radiocarbon dates the Finnish territory was entirely deglaciated slightly after 9000 B. P.     

Active ice-sheet deglaciation and ice-dammed lakes in the northern Cairngorm Mountains, Scotland

Mapping of ice-marginal and glaciolacustrine deposits in the northern Cairngorm Mountains allows the nature of deglaciation following the Last Glacial Maximum (c.18 000 BP) to be reinterpreted. Two ice-dammed lakes were ponded between the Glenmore lobe of the Scottish ice sheet and local glaciers draining northwards from the Cairngorm Mountains. Delta progradation from the southern end of each lake reflects dominant meltwater sources and glacio-hydrological gradients. Sediment facies representing subaqueous mass-flow deposits, lakebottom rhythmites, lower and upper foresets and topsets are associated with prograding delta fronts. Moraines show that the lakes were ice dammed at both ends, evidence that active glaciers existed in the Cairngorm Mountains while ice was retreating from Strath Spey, and that deglaciation was punctuated by readvances of the ice margin. These results indicate that an ice-stagnation model of deglaciation is invalid for most of the duration of ice wastage, but instead support an active-retreat hypothesis with multiple, climatically forced readvances.     

Glacial deposits and Late Weichselian ice-sheet dynamics in the northeastern Baltic Sea

Glacial deposits and landforms, interpreted from the continuous seismic reflection data, have been used to reconstruct the Late Weichselian ice-sheet dynamics and the sedimentary environments in the northeastern Baltic Sea. The bedrock geology and topography played an important role in the glacial dynamics and subglacial meltwater drainage in the area. Drumlins suggest a south-southeasterly flow direction of the last ice sheet on the Ordovician Plateau. Eskers demonstrate that subglacial meltwater flow was focused mostly within bedrock valleys. The eskers have locally been overlain by a thin layer of till. Thick proximal outwash deposits occupy elongated depressions in the substratum, which often occur along the sides of esker ridges. Ice-marginal grounding-line deposit in the southern part of the area has a continuation on the adjacent Island of Saaremaa. Therefore, we assume that its formation took place during Palivere Stadial of the last deglaciation, whereas the moraine bank extending southwestward from the Serve Peninsula is tentatively correlated with the Pandivere Stadial. The wedge-shaped ice-marginal grounding-line deposit was locally fed by subglacial meltwater streams during a standstill or slight readvance of the ice margin. The thickness of the glacier at the grounding-line was estimated to reach approximately 180 m. In the western part of the area, terrace-like morphology of the ice-marginal deposit and series of small retreat moraines 10–20 km north of it suggest stepwise retreat of the ice margin. Therefore, a rather thin and mobile ice stream was probably covering the northeastern Baltic Sea during the last deglaciation.     

Ice-Sheet Glaciation of the Puget lowland, Washington, during the Vashon Stade (late pleistocene)

During the Vashon Stade of the Fraser Glaciation, about 15,000–13,000 yr B.P., a lobe of the Cordilleran Ice Sheet occupied the Puget lowland of western Washington. At its maximum extent about 14,000 yr ago, the ice sheet extended across the Puget lowland between the Cascade Range and Olympic Mountains and terminated about 80 km south of Seattle. Meltwater streams drained southwest to the Pacific Ocean and built broad outwash trains south of the ice margin. Reconstructed longitudinal profiles for the Puget lobe at its maximum extent are similar to the modern profile of Malaspina Glacier, Alaska, suggesting that the ice sheet may have been in a near-equilibrium state at the glacial maximum. Progressive northward retreat from the terminal zone was accompanied by the development of ice-marginal streams and proglacial lakes that drained southward during initial retreat, but northward during late Vashon time. Relatively rapid retreat of the Juan de Fuca lobe may have contributed to partial stagnation of the northwestern part of the Puget lobe. Final destruction of the Puget lobe occurred when the ice retreated north of Admiralty Inlet. The sea entered the Puget lowland at this time, allowing the deposition of glacial-marine sediments which now occur as high as 50 m altitude. These deposits, together with ice-marginal meltwater channels presumed to have formed above sea level during deglaciation, suggest that a significant amount of postglacial isostatic and(or) tectonic deformation has occurred in the Puget lowland since deglaciation.     

Ice-lobe formation and function during the deglaciation in Finland and adjacent Soviet Karelia

The mode and nature of ice-flow mechanism leading to ice-lobe formation during deglaciation is described. These mechanisms are deduced primarily from their geomorphological and stratigraphical effects: the arc-like formations fringing the ice lobes, certain patterns of landform elements, and in some cases the stratigraphical signs indicating ice-marginal readvance or lack of it. Several ice-lobe creation mechanisms are presented along with the associated landform patterns they produce. The theory encompassing the fan-like ice flows, the ice-lobe formation, and the arc formations fringing them is applied to the deglaciation in Soviet Karelia and adjacent Finland. Deglaciation proceeded here from the southeast to the northwest, and complex arc formations derived from the major ice lobes. The Finnish Lake District lobe, the North Karelian lobe, the Kuusamo lobe, and the other lobes in northeastern Finland were in general metachronously formed.     

Deglaciation of the younger dryas or Loch Lomond Stadial ice-field in the northern Highlands,Scotland

When viewed from the air, Scottish ‘hummocky moraine’ can be resolved into a series of linear ridges that resemble those found at the margins of actively retreating glaciers today. Recent work has supported the interpretation of these linear ridges as ice-marginal landforms and the authors believe that the majority of ‘hummocky moraine’ deposits can be interpreted in this way. Consequently the pattern of deglaciation can be established fairly precisely from the pattern of linear ridges. This approach is applied to the landforms of the northern part of the Loch Lomond Stadial ice-field in order to reconstruct the regional pattern of deglaciation. This leads to important inferences about the significance of topographic control during deglaciation and more importantly it provides fresh insight into the environment of the British Isles during the Loch Lomond Stadial.     

The last glaciation of the Arctic volcanic island Jan Mayen

The volcanic island of Jan Mayen, remotely located in the Norwegian-Greenland Sea, was covered by a contiguous ice cap during the Late Weichselian. Until now, it has been disputed whether parts of the island south of the presently glaciated Mount Beerenberg area were ever glaciated. Based on extensive field mapping we demonstrate that an ice cap covered all land areas and likely also extended onto the shallow shelf areas southeast and east of the island. Chronological interpretations are based on K-Ar and ⁴⁰Ar/³⁹Ar dating of volcanic rocks, cosmogenic nuclide (³⁶Cl) surface exposure dating of bedrock and glacial erratics, and radiocarbon dating. We argue that ice growth started after 34 ka and that an initial deglaciation started some 21.5–19.5 ka in the southern and middle parts of the island. In the northern parts, closer to the present glaciers, the deglaciation might have started later, as evidenced by the establishment of vegetation 17–16 cal. ka BP. During full glaciation, the ice cap was likely thickest over the southern part of the island. This may explain a seemingly delayed deglaciation compared with the northern parts despite earlier initial deglaciation. In a broader context, the new knowledge of the Late Weichselian of the island contributes to the understanding of glaciations surrounding the North Atlantic and its climate history.     

Structural and depositional evidence for repeated ice-marginal oscillation along the eastern margin of the Late Devensian Irish Sea Ice Stream

Late Devensian glacigenic sediments and landforms along the north-west coast of Wales document the advance and subsequent retreat of the eastern margin of an Irish Sea Ice Stream that met, coalesced and ultimately uncoupled from ice radiating outwards from the adjacent Welsh Ice Cap centred over Snowdonia. Across the boundary between the two former ice masses is a set of sediment–landform assemblages that reflect rapidly changing erosional and depositional conditions during ice interaction. From the inner part of the ice-stream the assemblages range outwards, from a subglacial depositional assemblage, characterised by drumlin swarms; through a subglacial erosional assemblage, marked by prominent bedrock scours and large subglacial rock channels; through an ice-marginal assemblage, identified by closely spaced, glaciotectonised push moraines and intervening marginal sandur troughs; into a freely expanding proglacial sandur and lacustrine delta assemblage. The ice-marginal assemblage provides evidence for numerous oscillatory episodes during retreat and at least 20 ice-marginal limits can be identified. At least 11 of these display multiple criteria for identifying readvance and, in the ideal case, is characterised by a moraine form built by localised tectonic stacking of diamict to the rear, fronted by a clastic wedge of ice-front alluvial fan gravel and intercalated flow till. The distribution of sediment–landform assemblages suggests a highly dynamic, convergent ice-stream flow pattern, with high ice velocity, a sharply delineated lateral shear margin, pervasive ice-marginal glaciotectonic deformation and a tightly focused ice-marginal sediment delivery system; all signature characteristics of contemporary ice streams.     

Ice-margin retreat and grounding-zone dynamics during initial deglaciation of the Storfjordrenna Ice Stream,western Barents Sea

Processes occurring at the grounding zone of marine terminating ice streams are crucial to marginal stability, influencing ice discharge over the grounding-line, and thereby regulating ice-sheet mass balance. We present new marine geophysical data sets over a ~30×40 km area from a former ice-stream grounding zone in Storfjordrenna, a large cross-shelf trough in the western Barents Sea, south of Svalbard. Mapped ice-marginal landforms on the outer shelf include a large accumulation of grounding-zone deposits and a diverse population of iceberg ploughmarks. Published minimum ages of deglaciation in this region indicate that the deposits relate to the deglaciation of the Late Weichselian Storfjordrenna Ice Stream, a major outlet of the Barents Sea–Svalbard Ice Sheet. Sea-floor geomorphology records initial ice-stream retreat from the continental shelf break, and subsequent stabilization of the ice margin in outer-Storfjordrenna. Clustering of distinct iceberg ploughmark sets suggests locally diverse controls on iceberg calving, producing multi-keeled, tabular icebergs at the southern sector of the former ice margin, and deep-drafted, single-keeled icebergs in the northern sector. Retreat of the palaeo-ice stream from the continental shelf break was characterized by ice-margin break-up via large calving events, evidenced by intensive iceberg scouring on the outer shelf. The retreating ice margin stabilized in outer-Storfjordrenna, where the southern tip of Spitsbergen and underlying bedrock ridges provide lateral and basal pinning points. Ice-proximal fans on the western flank of the grounding-zone deposits document subglacial meltwater conduit and meltwater plume activity at the ice margin during deglaciation. Along the length of the former ice margin, key environmental parameters probably impacted ice-margin stability and grounding-zone deposition, and should be taken into consideration when reconstructing recent changes or predicting future changes to the margins of modern ice streams.     

Major shoreline retreat and sediment starvation following Snowball Earth

While cap dolostones are integral to the Snowball Earth hypothesis, the current depositional model does not account for multiple geological observations. Here we propose a model that rationalises palaeomagnetic, sequence‐stratigraphic and sedimentological data and supports rapid deglaciation with protracted cap dolostone precipitation. The Snowball Earth hypothesis posits that a runaway ice‐albedo can explain the climate paradox of Neoproterozoic glacial deposits occurring at low palaeolatitudes. This scenario invokes volcanic degassing to increase atmospheric greenhouse gases to a critical threshold that overcomes the albedo effect and brings the planet back from the ice‐covered state. Once this occurs, Earth should shift rapidly from a snowball to an extreme greenhouse. However, cap dolostone units overlying glacial sediments, typically interpreted as transgressive deposits, exhibit multiple magnetic reversals indicating they accumulated in >10⁵ years. By reviewing modern post‐glacial systems, sequence stratigraphic concepts and principles of sedimentology, we suggest that cap dolostones are not restricted to the transgression but rather represent sediment starvation following a major landward shoreline migration associated with the demise of Snowball Earth. Thus, the duration in which cap dolostone accumulated is not directly coupled to the timescale of the Snowball Earth deglaciation.     

Wastage features of the inland ice sheet in central South Norway

Detailed field mapping of different lateral phenomena, striae, texture and till fabric forms the basis of a reconstruction of five deglaciation phases in the east Jotunheimen-Gudbrandsdalen area, a land scape with moderate relief in the vicinity of the ice divide. During wastage, the inland ice sheet separated into several ice lobes situated in valleys enclosed by large ice-free uplands. The slope of the ice surface varied with local changes in the ice movement pattern and with the breaking of ice dams, which caused reversal of drainage from ice-dammed lakes. Non-climatic, large margianl moraines are thought to have fomed as a result of locally increased steepness of the ice surface. By tracing the deglaciation phases through two different valley systems which converge in the lake Mjøsa area, deglaciation events in the ice divide zone are correlated with marginal deposits at the front of the ice lobes.     

Evidence for Heinrich event 1 in the British Isles

In the north Irish Sea basin (ISB), sedimentary successions constrained by AMS ¹⁴C dates obtained from marine microfaunas record three major palaeoenvironmental shifts during the last deglacial cycle. (i) Marine muds (Cooley Point Interstadial) dated to between 16.7 and 14.7 ¹⁴C kyr BP record a major deglaciation of the ISB following the Late Glacial Maximum (LGM). (ii) Terminal outwash and ice-contact landforms (Killard Point Stadial) were deposited during an extensive ice readvance, which occurred after 14.7 ¹⁴C kyr BP and reached a maximum extent at ca.14 ¹⁴C kyr BP. At this time the lowlands surrounding the north ISB were drumlinised. Coeval flowlines reconstructed from these bedforms end at prominent moraines (Killard Point, Bride, St Bees) and indicate contemporaneity of drumlinisation from separate ice dispersal centres, substrate erosion by fast ice flow, and subglacial sediment transfer to ice-sheet margins. In north central Ireland bed reorganisation associated with this fast ice-flow phase involved overprinting and drumlinisation of earlier transverse ridges (Rogen-type moraines) by headward erosion along ice streams that exited through tidewater ice margins. This is the first direct terrestrial evidence that the British Ice Sheet (BIS) participated in Heinrich event 1 (H1). (iii) Regional mud drapes, directly overlying drumlins, record high relative sea-level (RSL) with stagnation zone retreat after 13.7 ¹⁴C kyr BP (Rough Island Interstadial). Elsewhere in lowland areas of northern Britain ice-marginal sediments and morainic belts record millennial-scale oscillations of the BIS, which post-date the LGM advance on to the continental shelf, and pre-date the Loch Lomond Stadial (Younger Dryas) advance in the highlands of western Scotland (ca. 11–10 ¹⁴C kyr BP). In western, northwestern and northern Ireland, Killard Point Stadial (H1) ice limits are reconstructed from ice-flow lines that are coeval with those in the north ISB and end at prominent moraines. On the Scottish continental shelf possible H1-age ice limits are reconstructed from dated marine muds and associated ice marginal moraines. It is argued that the last major offshore ice expansion from the Scottish mountains post-dated ca. 15 ¹⁴C kyr BP and is therefore part of the H1 event. In eastern England the stratigraphic significance of the Dimlington silts is re-evaluated because evidence shows that there was only one major ice oscillation post-dating ca.18 ¹⁴C kyr BP in these lowlands. In a wider context the sequence of deglacial events in the ISB (widespread deglaciation of southern part of the BIS → major readvance during H1 → ice sheet collapse) is similar to records of ice sheet variability from the southern margins of the Laurentide Ice Sheet (LIS). Well-dated ice-marginal records, however, show that during the Killard Point readvance the BIS was at its maximum position when retreat of the LIS was well underway. This phasing relationship supports the idea that the BIS readvance was a response to North Atlantic cooling induced by collapse of the LIS. © 1998 John Wiley & Sons, Ltd.     

Lateglacial ice dynamics of the Cordilleran Ice Sheet in northern British Columbia and southern Yukon Territory: retreat pattern of the Liard Lobe reconstructed from the glacial landform record

The Liard Lobe formed a part of the north‐eastern sector of the Cordilleran Ice Sheet and drained ice from accumulation areas in the Selwyn, Pelly, Cassiar and Skeena mountains. This study reconstructs the ice retreat pattern of the Liard Lobe during the last deglaciation from the glacial landform record that comprises glacial lineations and landforms of the meltwater system such as eskers, meltwater channels, perched deltas and outwash fans. The spatial distribution of these landforms defines the successive configurations of the ice sheet during the deglaciation. The Liard Lobe retreated to the west and south‐west across the Hyland Highland from its local Last Glacial Maximum position in the south‐eastern Mackenzie Mountains where it coalesced with the Laurentide Ice Sheet. Retreat across the Liard Lowland is evidenced by large esker complexes that stretch across the Liard Lowland cutting across the contemporary drainage network. Ice margin positions from the late stage of deglaciation are reconstructed locally at the foot of the Cassiar Mountains and further up‐valley in an eastern‐facing valley of the Cassiar Mountains. The presented landform record indicates that the deglaciation of the Liard Lobe was accomplished mainly by active ice retreat and that ice stagnation played a minor role in the deglaciation of this region. Copyright © 2013 John Wiley & Sons, Ltd.     

A polyphase glacitectonic model for ice-marginal retreat and terminal moraine development: the Middle Pleistocene British Ice Sheet,northern Norfolk,UK

Recent investigations from modern environments demonstrate that many terminal moraines do not simply record a single glacial maximum, but instead reveal a complex oscillatory pattern of ice-marginal behaviour including polyphase retreat. Within this study, we examine the geomorphology, geology and internal structure of a terminal moraine complex – the ‘Cromer Ridge’ in north Norfolk to reconstruct patterns of ice-marginal behaviour. Previously, this landform was interpreted as the limit of a southern extension of the British Ice Sheet during a Middle Pleistocene glaciation. Evidence presented here reveals a more complicated pattern of ice-marginal behaviour with the ‘Cromer Ridge’ reinterpreted as a ‘complex’ comprising several ridge elements. We propose that the maximum ice extent lay further to the south, with the size and morphology of the largest ridge element (the ‘Cromer Ridge’ as previously defined) a facet of thrust-stacking at an ice-marginal still-stand. We recognise multiple oscillations of the ice-front recorded against a twelve-stage model for the decay of the southern margins of a fast-flowing lobe of North Sea ice. Changes in ice-marginal dynamics are identified by the superimposition and lateral and vertical evolution of glacitectonic styles. Differences between these various states, and switches between ‘shallow’ and ‘deep’ thin-skinned glacitectonics, are strongly influenced by sub-marginal and proglacial water availability. Examination of the evidence for the morphostratigraphic proposals for the glacitectonic assemblage, within the context of the above interpretation, suggests that many of the ‘glacigenic landforms’ are erosional and a MIS 12 age of formation is favoured although several anomalies remain to be explained.     

Seafloor evidence for palaeo-ice streaming and calving of the grounded Irish Sea Ice Stream: Implications for the interpretation of its final deglaciation phase

High resolution swath bathymetry data reveal a previously glaciated submarine terrain 20 km offshore Anglesey, north Wales, UK. The detailed documentation of remarkably well-preserved subglacial and ice-marginal bedforms provides evidence for a grounded part of the Irish Sea Ice Stream in a phase of deglaciation. The observed ribbed moraines, drumlins, flutes and eskers indicate a converging ice flow to the west, which then turns south into the deeper central Irish Sea Basin. Using the relative position of the bedforms, their spatial distribution and the morphological resemblance with bedforms described in the literature, this subglacial terrain is interpreted as representing a transition zone of frozen to thawed bed conditions during deglaciation, with an eastwards migrating thawing front that partly altered the edge of the surveyed ribbed moraine field by drumlinization. The abundant De Geer moraines and iceberg scour marks superimposed on drumlins and flutes reveal that the final retreat of the grounded ice margin in the surveyed area terminated into a water-mass with extensive iceberg calving. As the glacial terrain is well preserved, no significant burial has taken place, either by glacially or terrestrially derived sediment. The strong tidal currents at present keep the submarine terrain swept clean of contemporary sediment cover.     

Glaciomarine varves and the character of deglaciation, Säveån valley, southwestern Sweden

Glaciomarine varves, in contrast to glaciolacustrine varves, are primarily dependent upon sedimentation from meltwater overflow. They are usually developed in proximal positions and are a more reliable reflection of deglaciation character within a specific area than 'classical' glaciolacustrine varves, which are generally more distal and greater influenced by bottom topography. The close relationship with ice-front processes in the glaciomarine environment is discussed and utilized to suggest correlations between the varve stratigraphy, ice-front positions and climate shifts during the deglaciation of the Savean valley, where two varve localities have been documented. A varve sequence outside this valley shows similar general trends in varve-thickness variation, and comparison between localities may help in extending the lines connecting positions of concurrent ice-marginal deposition. The study of glaciomarine varves provides a more continuous record of changes in the ice-front character than can be obtained from intermittent moraine positions.     

Younger Dryas deglaciation at Mt. Billingen, and clay varve dating of the Younger Dryas/Preboreal transition

A clay varve chronology has been established for the Late Weichselian ice recession east of Mt. Billingen in Västergötland, Sweden. In this area the Middle-Swedish end moraine zone was built up as a consequence of cold climate during the Younger Dryas stadial. A change-over from rapid to slow retreat as a result of climatic deterioration at the Alleröd/Younger Dryas transition cannot be traced with certainty in the varve sequences, but it seems to have taken place just before 11,600 varve years BP. The following deglaciation was very slow for about 700 years — within the Middle-Swedish end moraine zone the annual ice-front retreat was only c . 10 m on average. A considerable time-lag is to be expected between the Younger Dryas climatic event and this period of slow retreat. The 700 years of slow retreat were succeeded by 200 years of more rapid recession, about 50–75 m annually, and then by a mainly rapid and uncomplicated retreat of the ice-front by 100–200 m/year or more, characterizing the next 1500 years of deglaciation in south and central Sweden. The change from about 50–75 m to 100–200 m of annual ice-front retreat may reflect the Younger Dryas/Preboreal transition. Clay-stratigraph-ically defined, the transition is dated at c . 10,740 varve years BP, with an error of +100 to -250 years. In the countings of ice layers in Greenland ice cores (GRIP and GISP-2) the end of the Younger Dryas climatic event is 800–900 years older. However, a climatic amelioration after the cold part of the Younger Dryas and in early Preboreal should rapidly be reflected by for example chemical components and dust in Greenland ice cores, and by increasing δ¹³C content in tree rings. On the other hand, the start of a rapid retreat of the inland ice margin can be delayed by several centuries. This can explain at least a part of the discrepancy between the time-scales.     

Chronology of deglaciation based on 10Be dates of glacial erosional features in the Grimsel Pass region, central Swiss Alps

Surface exposure dating, using in situ produced cosmogenic ¹⁰Be, is applied to determine the time since deglaciation of bedrock surfaces in the Grimsel Pass region. Nine ¹⁰Be dates from bedrock surfaces corrected for cover by snow are minimum ages for deglaciation of the pass. Four ¹⁰Be dates from surfaces below 2500 meters above sea level (m a.s.l.) on Nägelisgrätli, east of Grimsel Pass, yield ages that range from about 14 000 to 11 300 years. Three ¹⁰Be dates from locations above 2600 m a.s.l. on Nägelisgrätli are between about 11 700 and 10 400 years. Two ¹⁰Be dates from locations at 2560 m a.s.l. below Juchlistock are about 12 100 and 11 000 years. The geographical distribution of ¹⁰Be dates on Nägelisgrätli either may show the timing of progressive deglaciation of Grimsel Pass or may reflect differences in subglacial erosion of bedrock in the pass region. All dates are discussed in the context of deglaciation of the late Würmian Alpine ice cap and deglaciation from Last Glacial Maximum (LGM) ice extents in other regions.     

Glacial deposits and ice-sheet dynamics in the north-central Baltic Sea during the last deglaciation

Nine seismic stratigraphic units were distinguished, and their distribution mapped, in an 80 × 130 km submeridionally oriented area in the north-central Baltic Sea, east of Gotska Sandön and Farö. Analysis of these units revealed a great influence of the bedrock topography on the structure and distribution of the glacial deposits. Major glacially eroded valleys in the Baltic Clint, connecting the Faro Deep and the North Central Baltic Basin (Harff & Winterhalter 1996) across a narrow sill, form an extensive submeridional bedrock depression. The concentration of ice flow into this depression is reflected in the drumlinized surface of the till near the Baltic Clint. Large eskers in the elongated bedrock depressions and on the Ordovician Plateau mark the locations of former subglacial meltwater conduits. Termination of the eskers with extensive glacio fluvial outwash fans at the northern limit of the Farö Deep, the presence of subaquatic melt-out till in the bottom of it, and wedge-shaped ice-marginal grounding-line deposit on the Silurian Plateau suggest floating ice margin conditions in the low-lying areas and a local ice shelf confined to the Frö Deep during the deglaciation.