Ice-flow Direction Research Articles

Great Mining Camps of Canada 7. The Bathurst Mining Camp, New Brunswick, Part 1: Geology and Exploration History

The Bathurst Mining Camp of northern New Brunswick is approximately 3800 km2 in area, encompassed by a circle of radius 35 km. It is known worldwide for its volcanogenic massive sulphide deposits, especially for the Brunswick No. 12 Mine, which was in production from 1964 to 2013. The camp was born in October of 1952, with the discovery of the Brunswick No. 6 deposit, and this sparked a staking rush with more hectares claimed in the province than at any time since. In 1952, little was known about the geology of the Bathurst Mining Camp or the depositional settings of its mineral deposits, because access was poor and the area was largely forest covered. We have learned a lot since that time. The camp was glaciated during the last ice age and various ice-flow directions are reflected on the physiographic map of the area. Despite abundant glacial deposits, we now know that the camp comprises several groups of Ordovician predominantly volcanic rocks, belonging to the Dunnage Zone, which overlie older sedimentary rocks belonging to the Gander Zone. The volcanic rocks formed during rifting of a submarine volcanic arc on the continental margin of Ganderia, ultimately leading to the formation of a Sea of Japan-style basin that is referred to as the Tetagouche-Exploits back-arc basin. The massive sulphide deposits are mostly associated with early-stage, felsic volcanic rocks and formed during the Middle Ordovician upon or near the sea floor by precipitation from metalliferous fluids escaping from submarine hot springs. The history of mineral exploration in the Bathurst Mining Camp can be divided into six periods: a) pre-1952, b) 1952-1958, c) 1959-1973, d) 1974-1988, and e) 1989-2000, over which time 45 massive sulphide deposits were discovered. Prior to 1952, only one deposit was known, but the efforts of three men, Patrick (Paddy) W. Meahan, Dr. William J. Wright, and Dr. Graham S. MacKenzie, focused attention on the mineral potential of northern New Brunswick, which led to the discovery of the Brunswick No. 6 deposit in October 1952. In the 1950s, 29 deposits were discovered, largely resulting from the application of airborne surveys, followed by ground geophysical methods. From 1959 to 1973, six deposits were discovered, mostly satellite bodies to known deposits. From 1974 to 1988, five deposits were found, largely because of the application of new low-cost analytical and geophysical techniques. From 1989 to 2000, four more deposits were discovered; three were deep drilling targets but one was at surface.

Ice-sheet scale distribution and morphometry of triangular-shaped hummocks (murtoos): a subglacial landform produced during rapid retreat of the Scandinavian Ice Sheet

AbstractHigh-resolution digital elevation models of Finland and Sweden based on LiDAR (Light Detection and Ranging) reveal subglacial landforms in great detail. We describe the ice-sheet scale distribution and morphometric characteristics of a glacial landform that is distinctive in morphology and occurs commonly in the central parts of the former Scandinavian Ice Sheet, especially up-ice of the Younger Dryas end moraine zone. We refer to these triangular or V-shaped landforms as murtoos (singular, ‘murtoo’). Murtoos are typically 30–200 m in length and 30–200 m in width with a relief of commonly <5 m. Murtoos have straight and steep edges, a triangular tip oriented parallel to ice-flow direction, and an asymmetric longitudinal profile with a shorter, but steeper down-ice slope. The spatial distribution of murtoos and their geomorphic relation to other landforms indicate that they formed subglacially during times of climate warming and rapid retreat of the Scandinavian Ice Sheet when large amounts of meltwater were delivered to the bed. Murtoos are formed under warm-based ice and may be associated with a non-channelized subglacial hydraulic system that evacuated large discharges of subglacial water.

Equifinality and preservation potential of complex eskers

Eskers are useful for reconstructing meltwater drainage systems of glaciers and ice sheets. However, our process understanding of eskers suffers from a disconnect between sporadic detailed morpho‐sedimentary investigations of abundant large‐scale ancient esker systems, and a small number of modern analogues where esker formation has been observed. This paper presents the results of detailed field and high‐resolution remote sensing studies into two esker systems that have recently emerged at Hørbyebreen, Svalbard, and one at Breiðamerkurjökull, Iceland. Despite the different glaciological settings (polythermal valley glacier vs. active temperate piedmont lobe), in all cases a distinctive planform morphology has developed, where ridges are orientated in two dominant directions corresponding to the direction of ice flow and the shape of the ice margin. These two orientations in combination form a cross‐cutting and locally rectilinear pattern. One set of ridges at Hørbyebreen is a hybrid of eskers and geometric ridges formed during a surge and/or jökulhlaup event. The other sets of ridges are eskers formed time‐transgressively at a retreating ice margin. The similar morphology of esker complexes formed in different ways on both glacier forelands implies equifinality, meaning that care should be taken when interpreting Quaternary esker patterns. The eskers at Hørbyebreen contain substantial ice‐cores with a high ice:sediment ratio, suggesting that they would be unlikely to survive after ice melt. The Breiðamerkurjökull eskers emerged from terrain characterized by buried ice that has melted out. Our observations lead us to conclude that eskers may reflect a wide range of processes at dynamic ice margins, including significant paraglacial adjustments. This work, as well as previous studies, confirms that constraints on esker morphology include: topographic setting (e.g. confined valley or broad plain); sediment and meltwater availability (including surges and jökulhlaups); position of formation (supraglacial, englacial or subglacial); and ice‐marginal dynamics such as channel abandonment, the formation of outwash heads or the burial and/or exhumation of dead ice.

Magnetic anisotropy and debris-dependent rheological heterogeneity within stratified basal ice

AbstractBasal ice of glaciers and ice sheets frequently contains a well-developed stratification of distinct, semi-continuous, alternating layers of debris-poor and debris-rich ice. Here, the nature and distribution of shear within stratified basal ice are assessed through the anisotropy of magnetic susceptibility (AMS) of samples collected from Matanuska Glacier, Alaska. Generally, the AMS reveals consistent moderate-to-strong fabrics reflecting simple shear in the direction of ice flow; however, AMS is also dependent upon debris content and morphology. While sample anisotropy is statistically similar throughout the sampled section, debris-rich basal ice composed of semi-continuous mm-scale layers (thestratified facies) possesses well-defined triaxial to oblate fabrics reflecting shear in the direction of ice flow, whereas debris-poor ice containing mm-scale star-shaped silt aggregates (thesuspended facies) possesses nearly isotropic fabrics. Thus, deformation within the stratified basal ice appears concentrated in debris-rich layers, likely the result of decreased crystal size and greater availability of unfrozen water associated with high debris content. These results suggest that variations in debris-content over small spatial scales influence ice rheology and deformation in the basal zone.

Seismic Noise Interferometry Reveals Transverse Drainage Configuration Beneath the Surging Bering Glacier

AbstractSubglacial drainage systems are known to critically control ice flows, but their spatial configuration and temporal evolution are poorly constrained due to inaccessibility. Here we report a 12‐year‐long monitoring of the drainage underneath Bering Glacier, Alaska, by correlating ambient noise recorded at two seismic stations on the sides of the glacier. We find that the seismic surface waves traveling across Bering Glacier slowed down by 1–2% during its latest 2008–2011 surge, likely due to the switch of the subglacial drainage from a channelized system to a distributed system. In contrast to current models, the relative amplitude of velocity reductions for Rayleigh and Love waves requires the distributed drainage to be highly anisotropic and aligned perpendicular to the ice flow direction. We infer that the subglacial water flow is mainly through a network of transverse basal crevasses during surges and thus can sustain the high water pressure and ice flow speed.

The local Last Glacial Maximum in McMurdo Sound, Antarctica: Implications for ice-sheet behavior in the Ross Sea Embayment

AbstractDuring the Last Glacial Maximum (LGM), a grounded ice sheet filled the Ross Sea Embayment in Antarctica and deposited glacial sediments on volcanic islands and peninsulas in McMurdo Sound and coastal regions of the Transantarctic Mountains. The flow geometry and retreat history of this ice are debated, with contrasting views yielding divergent implications for the interaction between and stability of the East and West Antarctic ice sheets during late Quaternary time. Here, we present terrestrial geomorphologic evidence and reconstruct former ice-marginal environments, ice sheet elevations, and ice-flow directions in McMurdo Sound. Fossil algae in ice-marginal sediments provide a coherent radiocarbon chronology of maximum ice extent and deglaciation. We integrate these data with marine records to reconstruct grounded ice dynamics in McMurdo Sound and the western Ross Sea. The combined data set suggests ice flow toward the Transantarctic Mountains in McMurdo Sound during peak glaciation, with thick, grounded ice at or near its maximum position between 19.6 and 12.3 ka. Persistent grounded ice in McMurdo Sound and across the western Ross Sea after Meltwater Pulse 1a (14.0–14.5 ka) suggests that this sector of Antarctica did not significantly contribute to this rapid sea-level rise event. Our data show no significant advance of locally derived ice from the Transantarctic Mountains into McMurdo Sound during the local LGM.

Electromagnetic resistivity anisotropy in till from the Kiskatinaw streamlined landform field, northeastern British Columbia, Canada

Applications of the azimuthal electromagnetic (EM) method that establish the internal structure of landforms consisting of sediment are sparse. In the Kiskatinaw streamlined landform field of northeastern British Columbia, ice-flow parallel till ridges formed beneath the Cordilleran Ice Sheet during the late Wisconsinan. EM anisotropy data from the Kiskatinaw field are systematically related to ridge elongation and orientation and, in part, to clast fabrics. However, in contrast to previous studies, we find that resistivity measurements do not necessarily record the orientation of ice flow, and electrical anisotropy in till may not be a simple indicator of ice-flow direction. For highly elongate ridges (l/w > 3), the long axes of resistivity ellipses are at high angles to the long axes of the landforms. Tills in these elongate ridges are matrix rich (>85%) and display strong unimodal ice-flow parallel clast fabrics. For more equant ridges (l/w < 3), the long axes of resistivity ellipses are at low angles to the long axes of the landforms. Tills in these ridges are clast rich (up to 60%) and display polymodal clast fabrics with both ice-flow parallel and ice-flow transverse modes. Because clast fabrics in the more equant ridges are so variable, despite unimodal resistivity patterns, and because groundwater well data indicate relatively fresh pore waters and the till matrix contains clay (average 12%), we speculate that the resistivity/conductivity anisotropy we observed may record aligned matrix clays rather than clast fabrics alone. We interpret that the highly elongate ridges indicate subglacial shear along a non-cohesive easily deformed bed, whereas the more equant ridges mark ‘sticky spots’ where high clast concentrations produced local areas that resisted subglacial shear and induced local ice-flow parallel shortening, which limited landform elongation and clast alignment.

Effect of shifting ice flow and basal topography in shaping three-dimensional dispersal patterns, Lac de Gras region, Northwest Territories, Canada

Tracing indicator minerals and geochemical pathfinders in glacial sediments back to their up-ice source is a common mineral exploration approach in prospective, formerly glaciated regions. In this study, we utilize surface and subsurface data from the Lac de Gras area of the Northwest Territories to develop a three-dimensional understanding of till compositional anomalies emanating from two known kimberlite pipes, DO-18 and DO-27. Specifically, this study examines the three-dimensional shape of dispersal trains as defined by geochemical pathfinder elements and kimberlite indicator minerals shed from a pair of kimberlite pipes within a till cover of variable thickness. From our ninety-four reverse circulation boreholes (n = 251 till samples), and other publicly-available geologic datasets, we have reconstructed bedrock topography, till thickness, and the subsurface geometry of two dispersal trains. Utilizing our three-dimensional dataset, we have documented the role of basal topography in creating dispersal patterns with contrasting geometries from two adjacent kimberlites, as well as in the preferential preservation of older till units. The combination of field observations of ice-flow indicators and till compositional data demonstrates that features produced by multiple ice flows are preserved in both the erosional and depositional records in this region. Three-dimensional dispersion patterns of kimberlite indicators reflect the effect of shifting ice-flow direction with respect to slope aspect of bedrock topography in governing compositional variability within glacial drift. Our findings suggest that surficial data do not capture the full extent of dispersion patterns even in areas of relatively thin and discontinuous till cover.

Glacial to postglacial submarine landform assemblages in fiords of northeastern Baffin Island

Fiord morphology plays a fundamental role in glacier flow dynamics and on ice-margin stability. As most of the present-day margins of the Greenland Ice Sheet lays in fiords, there is a need for understanding short- and long-term glacial dynamics in fiord settings. We investigate ice-sheet retreat patterns in previously glaciated submarine terrain of northeastern Baffin Island fiords to provide analogues for modern and future ice-sheet response to climate change and sea-level rise. Geomorphological maps constructed from the interpretation of swath bathymetry imagery in fiords of northeastern Baffin Island reveal a wide range of glacial to postglacial landforms that allow the reconstruction of past ice-sheet retreat dynamics. Ice-flow landforms such as mega-scale glacial lineations, crag-and-tails, and meltwater channels reveal the direction and behaviour of late-Foxe ice flow through the fiords. The presence of undisturbed elongated landforms within the fiords suggests that ice streams have probably been active until the late stage of deglaciation. Landforms transverse to ice-flow direction include grounding-zone wedges, frontal moraines, grounding-line fans, recessional moraines and De Geer moraines. These landforms are interpreted as the result of former standstills of the ice margin during deglaciation. The occurrence of grounding zones in deep (>800 m) part of the fiords contrasts with studies suggesting instability and rapid retreat of outlet glaciers over deep fiord basins. Sediment-filled basins, often characterised by the presence of turbidity channels, gullies and mass movement scars occur in-between the moraines. Sediment-filled basins with a ponded architecture between sills illustrate that most of the sediment accumulation was ice-proximal during deglaciation and characterised by gravity-driven flows. The proposed landform-assemblage model for northeastern Baffin fiords includes landforms typical of different fiord landsystems.

Glacial geology of Saalian relief around Midwolda, eastern Groningen, the Netherlands

AbstractDue to canal-digging activities in 2011 and 2014, two small and one large temporary exposure, all ranging from 4 to 5 m in depth, were studied with respect to the sedimentology and structural geology, in the glacial ridge of Midwolda, Groningen, the Netherlands. The lowermost unit consists of clay of Elsterian age and is composed of glaciolacustrine and turbiditic deposits (Peelo Formation). These show synsedimentary deformations due to loading, as well as post-sedimentary Saalian glaciotectonic deformations, consisting of folding, and faulting structures. The overlying Saalian till sequence consists of two main units. The lower unit, with clear features of a subglacial deformation zone (e.g. lateral heterogeneity), has a local origin and strongly resembles the underlying Elsterian clay. Glacial tectonic and morphological observations indicate a primary NE–SW ice-flow direction. The second till layer has a sandy texture and high crystalline gravel content, while glacial-tectonic indicators point to a NW–SE ice-flow direction. The deformation of the till layers has caused a repetition and mixing of till layers, due to the last ice movement. The NW–SE ice movement is supported by the morphology as well as data from erratic gravel counts. Correlation with geological cross-sections strongly suggests regional subsurface control on ice-sheet behaviour.

EXTRACTION OF BLUE ICE AREA USING ALBEDO VALUE DERIVED FROM LANDSAT-8 SATELLITE DATA

Abstract. Blue Ice Areas (BIAs) or bare ice areas are zones of glacier where surface mass balance is negative, sublimation forms the major ablation process and surface albedo is relatively small. Exceptionally dry and windy meteorological conditions over Antarctica favor the formation of large areas of net ablation on the ice sheet leading to formation of BIRs (Schytt, 1961). BIAs are major source of drinking water to research stations and serve as runways for airplanes in Antarctica. This study has been conducted on the Polar Record Glacier (PRG), Princess Elizabeth Land, East Antarctica, where more than 30% of area is covered by BIAs. The BIAs are extracted and estimated using the value of albedo which is the fraction of solar energy reflected from the surface back to space. A surface having a higher (lower) reflectivity occupies higher (lower) albedo. With an average value of blue ice albedo (also known as bare ice) of 0.55, it ranges from 0.52 to 0.66, due to its geographical area, katabatic wind and wind patterns, the direction of ice flow, rate of sublimation and ablation, surface temperature, etc. The extent of BIAs also depends upon climate and seasonal changes. Albedo is calculated using the Level-1 product of Landsat, this data product (images) is processed according to standard parameters such as Geo-referencing, re-sampling, re-projection and north-up image re-orientation. These data (Digital Numbers) were further calibrated to standard pixel value using multiplicative and additive rescaling factors from metadata provided with the Level-1 product and scaled for absolute reflectance. A further algorithm was applied to get albedo from Landsat-8 dataset. After processing the data, we detected some error in a few pixels, (∼20) which was normalized by using band math. Our result indicates that the range of albedo for the BIAs is decreasing (more surface absorption of solar radiation), which subsequently could promote warming of surface due to increase in the surface temperature. The decreasing rate of albedo suggest the possibility of less reflection of radiation to the atmosphere, more melting which leads to depletion in the BIAs. The carry home message is that the variation in different parameters like albedo of the glacier causes significant variation in the surface area and spatial extent of BIAs.

Differential Geometry of Ice Flow

Flowlines on ice sheets and glaciers form complex patterns. To explore their role in ice routing and extend the language for studying such patterns, we develop a theory of flow convergence and curvature in plan view. These geometric quantities respectively equal the negative divergence of the vector field of ice-flow direction and the curl of this field. From the first of these two fundamental results, we show that flow in individual catchments of an ice sheet can converge (despite its overall spreading) because ice divides are loci of strong divergence, and that a sign bifurcation in convergence occurs during ice-sheet 'symmetry breaking' (the transition from near-radial spreading to spreading with substantial azimuthal velocities) and during the formation of ice-stream tributary networks. We also uncover the topological control behind balance-flux distributions across ice masses. Notably, convergence participates in mass conservation along flowlines to amplify ice flux via a positive feedback; thus the convergence field governs the form of ice-stream networks simulated by balance-velocity models. The theory provides a roadmap for understanding the tower-shaped plot of flow speed versus convergence for the Antarctic Ice Sheet.

Holocene reconfiguration and readvance of the East Antarctic Ice Sheet

How ice sheets respond to changes in their grounding line is important in understanding ice sheet vulnerability to climate and ocean changes. The interplay between regional grounding line change and potentially diverse ice flow behaviour of contributing catchments is relevant to an ice sheet’s stability and resilience to change. At the last glacial maximum, marine-based ice streams in the western Ross Sea were fed by numerous catchments draining the East Antarctic Ice Sheet. Here we present geomorphological and acoustic stratigraphic evidence of ice sheet reorganisation in the South Victoria Land (SVL) sector of the western Ross Sea. The opening of a grounding line embayment unzipped ice sheet sub-sectors, enabled an ice flow direction change and triggered enhanced flow from SVL outlet glaciers. These relatively small catchments behaved independently of regional grounding line retreat, instead driving an ice sheet readvance that delivered a significant volume of ice to the ocean and was sustained for centuries.

Past ice stream and ice sheet changes on the continental shelf off the Sabrina Coast, East Antarctica

Our understanding of the response of the Antarctic ice sheet to climate and ocean changes requires the improvement of current ice-atmosphere-ocean models and the accurate determination of boundary conditions such as ice thickness and extent at key time intervals, so that satellite gravity observations and isostatic models can be adjusted. However, large portions of the Antarctic margin remain understudied or lack suitable data. One key area where data are lacking, is the Sabrina Coast portion of the East Antarctic Ice Sheet (EAIS) margin where the Totten Glacier, which has the largest ice discharge in East Antarctica, is accelerating, thinning and loosing mass at high rates. In this work, we present the results of the first geological and geophysical marine survey to the continental shelf offshore of the Dalton Ice Tongue and Moscow University ice shelf, east of the Totten Glacier. The data presented include multibeam swath bathymetry and multichannel seismic, focusing on the sea floor morphology and sedimentary section above a regional angular unconformity separating pre- and post-Miocene glacial strata. Sea floor scouring and iceberg keel marks on the outer shelf, associated with gullies on the upper slope indicate that ice expanded in the past and grounded ~5 km from the shelf edge at ~450–500 mbsl, extending ~155 km north of the current Moscow University Ice Shelf. A nearly 1000 m deep area in the inner-middle shelf, oriented NW with paleo-ice flow direction indicated by mega scale glacial lineations (MSGL) and drumlins, is interpreted as a cross shelf glacial trough. A series of geomorphic associations on the north-eastern side of the glacial trough includes glacial lobes, grounding zone wedges (GZW), glacial lineations and transverse ridges, which indicates slower ice, grounding line stabilization and collapse. These geomorphic associations are organized in 4 four sets representing different past ice-flow configurations reflecting changes in ice flow direction, grounding line position, location of fast and slow ice areas, and retreat pattern. Some of the geomorphic features identified are compatible with the presence of an organized subglacial drainage, and others are with rapid grounding line collapse. A well-preserved series of GZWs occurring at different water depths implies they were formed during different glacial stages or cycles. The inferred diminishing ice thickness for consecutives GZWs indicates that the margin of the Antarctic ice sheet evolved to a less extensive coverage of the continental shelf through successive glacial stages or cycles.The identification of different ice flow configurations, evidence of subglacial water and past ice margin collapse indicates a dynamic ice sheet margin with varying glacial conditions and retreat modes. We observe that some of the described morphological associations are similar to those found in the Amundsen sea sector of the West Antarctic Ice Sheet (WAIS) where they are associated with ice sheet and ice stream collapse. Although further studies are needed to assess the precise timing and rates of the glacial processes involved, we conclude that there is enough evidence to support the hypothesis that the EAIS margin can behave as dynamically as the WAIS margin, especially during glacial retreat and icesheet margin collapse.

Indicator minerals of the Meliadine orogenic gold deposits, Nunavut (Canada), and application to till surveys

The Meliadine Gold District is located about 25 km north of Rankin Inlet, Nunavut (Canada), in the Archean Rankin Inlet greenstone belt. The bedrock is composed of greenschist facies metamorphic rocks. The composition of tourmaline and scheelite is investigated by electron probe micro-analyser (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA ICP-MS). The chemical composition of these indicator minerals from the Meliadine deposits is compared with the composition of grains extracted from till samples along a 2 km transect parallel to the direction of ice flow at the Mustang showing. Tourmaline from the deposit is characterized by a flat rare earth element (REE) pattern having a positive europium anomaly also found in tourmaline grains in till samples down-ice of the Mustang showing. Scheelite from the Mustang showing shows a bell-shaped REE pattern with a negative europium anomaly, which is also found in scheelite from down-ice till samples. Scheelite and tourmaline recovered from till down-ice from the Mustang showing have a composition diagnostic of the gold mineralization. Determining the composition of tourmaline and scheelite in unconsolidated sediments can serve to identify gold mineralization and has the potential to be applied in mineral exploration in the Meliadine Gold District and elsewhere.

Relationship between mega-scale glacial lineations and iceberg ploughmarks on the Bjørnøyrenna Palaeo-Ice Stream bed, Barents Sea

Mega-scale glacial lineations (MSGLs) are ridge-groove corrugations aligned in the direction of the former ice flow, tens of kilometers long and up to a few hundred meters wide. They are the most striking subglacial features on the beds of former ice streams and play an important role in modulating ice flow through their influence on bed roughness and subglacial hydrology. Despite the importance of MSGLs, their formation remains enigmatic. Most studies have tended to focus on assemblages of MSGLs and their relationship to other landforms up-ice (e.g. drumlins or bedrock features in ice stream onset zones) but fewer studies have examined their characteristics and transition to other landforms towards ice stream grounding lines. In this paper we investigate the relationship between an assemblage of MSGLs and ploughmarks on the bed of the former Bjørnøyrenna Ice Stream in the SW Barents Sea, which occurs in the central part of the ice stream bed. A sample of MSGLs is used to test their potential origin, based on their metrics (width, length) and diagnostic characteristics predicted by formation theories. Results show a down-flow depth decrease of the MSGL grooves, and a shallowing tendency once they transition into ploughmarks. Their width shows an increasing tendency, which we link mostly to the strong divergence of the trough (and ice flow) downstream. The prominent continuity from linear to curvilinear features demonstrates that the grooves associated with MSGLs transition into iceberg ploughmarks. This observation is consistent with the hypothesis that the MSGLs have formed through a mechanism of “groove-ploughing”, at least in part. The continuity from MSGLs to iceberg ploughmarks resulted from detachment of large icebergs from the grounded ice wall or grounded ice shelf and their ploughing away from the ice margin.

Irish Ice Sheet dynamics during deglaciation of the central Irish Midlands: Evidence of ice streaming and surging from airborne LiDAR

High resolution digital terrain models (DTMs) generated from airborne LiDAR data and supplemented by field evidence are used to map glacial landform assemblages dating from the last glaciation (Midlandian glaciation; OI stages 2–3) in the central Irish Midlands. The DTMs reveal previously unrecognised low-amplitude landforms, including crevasse-squeeze ridges and mega-scale glacial lineations overprinted by conduit fills leading to ice-marginal subaqueous deposits. We interpret this landform assemblage as evidence for surging behaviour during ice recession. The data indicate that two separate phases of accelerated ice flow were followed by ice sheet stagnation during overall deglaciation. The second surge event was followed by a subglacial outburst flood, forming an intricate esker and crevasse-fill network. The data provide the first clear evidence that ice flow direction was eastward along the eastern watershed of the Shannon River basin, at odds with previous models, and raise the possibility that an ice stream existed in this area. Our work demonstrates the potential for airborne LiDAR surveys to produce detailed paleoglaciological reconstructions and to enhance our understanding of complex palaeo-ice sheet dynamics.

Evidence for a grounded ice sheet in the central North Sea during the early Middle Pleistocene Donian Glaciation

Interpretation of 3D seismic data from the central North Sea yields evidence of a pre-MIS (Marine Isotope Stage) 12 grounded glaciation. The glaciotectonic complex shows buried push moraines resulting from the thrusting of multiple ice advance phases with horizontal shortening of 35 – 50%. The earliest feature observed within the complex, a hill–hole pair, represents the initial glaciation of the area. This is overlain and deformed by multiple thrust units with numerous inferred ice-flow directions. The thrust deformation observed shares characteristics with kinematic processes, push moraines and static gravity processes, seen as gravity spreading and contraction. The glaciotectonic complex in its entirety is interpreted to correlate to a pre-Elsterian glaciation, becaue of its stratigraphic position below central North Sea tunnel valleys, estimated to be Elsterian in age (MIS 12; 450 ka). The study proposes that the thrust complex correlates to the Donian glaciation in Russia (MIS 16; 600 ka) with ice sourced from Norway. The complex therefore represents a glaciation where a significant area of the central North Sea was covered by an ice sheet, 200 kyr prior to the Elsterian. This study highlights the fragmentary record of pre-Elsterian glaciations and the importance of incorporating offshore sedimentary archives and regional frameworks when reconstructing Pleistocene climate change.

Ice-flow directions of the last Scandinavian Ice Sheet in central Poland

The article presents the results of studies on the ice-flow directions of the last Scandinavian Ice Sheet (SIS) in central Poland, at the southern periphery of the SIS, and particularly within the Płock lobe. The ice-flow pattern was derived mainly from direct indices, such as: till fabric; vergence of glaciotectonic compression structures; orientation of small-scale subglacial deformations formed beneath the flowing ice; orientation of pavement stone longitudinal axes; stone lee ends; and clast surface striae. The study is supplemented with a reconstruction of ice-movement directions based on orientation analysis of both concave (tunnel valley) and convex (eskers) glacial morpholineaments (linear glacial landforms). Till age was also determined, using luminescence (OSL) datings from sand deposits. These were collected directly at numerous sites, from under and above the last SIS till unit. Combined with previously published data, the results of the present investigation of the last ice-sheet advance during the Late Weichselian (ca 23–18 ka) indicate that there were two different ice-flow phases and that the maximum extent was asynchronous. The western part of the said area experienced two advances during the Leszno (Brandenburg) and Poznań (Frankfurt) phases, while during the earlier one the ice masses came from the NW, presumably along the eastern limb of the Odranian (B2 after Punkari 1997) ice stream, and then from the N, along the Vistulian (B3) stream. The last SIS occupied the eastern sector of the area only once, during the younger Poznań phase, building the Płock lobe. The lobe-shaped ice margin with a fan-like flow pattern within the lobe may be indicative of a palaeo-ice stream terminal zone.

Directional properties of glacial relief and sediments as an effect of multi-stage evolution: Case study of the Tczew Hump, northern Poland

This paper focuses on the upland territory south-west of the Gulf of Gdańsk characterized by the existence of numerous hills with distinct ordering of their crest-line orientation. Characteristic features of relief in the Tczew Hump were analysed using GIS-based tools. Directional properties and morphometric characteristics are not uniform throughout the study area. Therefore, subsequent detailed analyses were performed after dividing it into three zones: north-western (NW), central and south-eastern (SE). The highest hills are situated in the central part of the Hump. The landforms analysed are mostly elongated, but they show varying elongation ratios (1.0–4.05). In general a NE-SW orientation is observed, however, the azimuthal distribution of their crest-lines shows considerable variation (from N-S to E-W). Two main systems of the crest-line orientation are distinguished: System A (NNE-SSW) and System B (NE-SW/ENE-WSW).The landforms considered are covered with till consisting of two subunits, what reflects two subsequent ice-sheet movement periods in the Late Weichselian but without releasing the area from ice-sheet cover. The subunits can be identified by changes in their petrographic composition – up to ten times more erratics of local provenance in the upper one than in the lower one. Ice flow direction during deposition of both till subunits, based on the till fabric of each of the three analysed sections, coincides with System A of the crest-lines. However, most of the till-covered hills fit System B, which suggests that they retained their previous (older than Late Weichselian) orientation. The complex relief of the Tczew Hump has a palimpsest nature and its arrangement emerged in several stages: (1) formation of the primeval relief before the Late Weichselian (hills built of sediments of heterogeneous ages); (2) partial relief reshaping in subglacial conditions during the two, successive, ice-flow events in the Late Weichselian (till-covered hills, clear bipartition of the till); (3) development of additional landforms during deglaciation − typically not covered with till (or with flow till on the slopes only), showing an orientation determined by the crevasse system developed in the ice.