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The study of palaeo-glacial landforms and sediments can give insights into the nature and dynamics of ice sheets. This is particularly the case with regards to the subglacial record, which is challenging to observe in contemporary glaciated settings and hence remains only partially understood. The subglacial hydrological system is an essential component of ice dynamics, where increased water pressure enhances ice motion and sediment deformation, thus reducing ice-bed contact. Tunnel valleys are large, sinuous, steep-sided incisions that, together with smaller scale meltwater channels, indicate subglacial meltwater discharge beneath large ice sheets. Through the use of high-resolution marine geophysical data, a system of buried and exposed tunnel valleys, possible subglacial or proglacial meltwater channels and palaeo-fluvial valleys have been identified across the shelf of the Celtic Sea between Ireland and Britain. The presence of steep-sided and overdeepened tunnel valleys is indicative of a large channelized meltwater drainage system beneath the former Irish Sea Ice Stream, the most extensive ice stream to drain the last British–Irish Ice Sheet. After the rapid ice expansion across the Celtic Sea shelf around 28–26 ka, the tunnel valleys were carved into both bedrock and glacigenic sediments and are associated with rapid ice stream retreat northwards into the Irish Sea Basin between 25.6 and 24.3 ka. The presence of a major subglacial meltwater system on the relatively shallow shelf suggests that significant erosive meltwater discharge occurred during the last deglaciation and highlights the important contribution of meltwater to the retreat of the British–Irish Ice Sheet on the continental shelf.

O Cofaigh, C., Evans, D. J. A. & Hiemstra, J. F. 2010: Formation of a stratified subglacial ‘till’ assemblage by ice-marginal thrusting and glacier overriding. Boreas, 10.1111/j.1502-3885.2010.00177.x. ISSN 0300-9483. A thick sequence of glaciotectonically stacked till and outwash is preserved in a coastal embayment at Feohanagh, southwest Ireland. The sequence contains a variety of diamicton lithofacies, including laminated, stratified and massive components, but stratified diamictons dominate. Stratification/lamination is imparted by the presence of numerous closely spaced subhorizontal and anastomosing partings, which give a fissile appearance to the diamictons. Many partings are the result of sandy or thin gravelly layers within the diamictons. Some diamictons contain interbeds and lenses of sand, mud and gravel, which still preserve the original stratification. The sequence at Feohanagh is the product of a two-stage depositional process in which initial glaciolacustrine sedimentation in an ice-dammed lake was followed by glaciotectonic thrusting and overriding, during which the lake sediments were reworked and variably deformed. Similar late Quaternary sequences of glaciotectonically stacked stratified sediments and till have been described from around the coastal margins of Ireland and Britain, where they constitute glaciotectonite–subglacial traction till continuums rather than true lodgement tills as traditionally implied. Thick stratified diamicton assemblages are likely to occur in areas where steep topography provides pinning points for the glacier margin to stabilize and deliver large volumes of sediment into a glaciolacustrine or glaciomarine setting before proglacial and subglacial reworking of the sediment pile. The resulting geological–climatic unit, often defined as ‘till’, will contain a large amount of stratified and variably deformed material (laminated and stratified diamictons will be common), including intact sediment rafts, reflecting low strain rates and short sediment transport distances.

This research reconstructs ice-sheet processes operating during the Late Devensian in northeast England. The article assesses the lithostratigraphy of the Devensian glacial tills of Whitburn Bay, eastern County Durham, and presents the first detailed analysis of petrological, geochemical and biostratigraphical data to reconstruct lithostratigraphy, provenance and iceflow pathways. Two Devensian tractions tills (the Blackhall and Horden tills) are separated by a boulder pavement, pointing to a switch in ice-bed conditions and the production of a melt-out lag prior to deposition of the upper traction till, the Horden Till. The Blackhall Till contains Magnesian Limestone, Carboniferous Limestone, Whin Sill dolerite and Old Red Sandstone, suggesting a northwesterly source, probably from the Midland Valley and the Southern Uplands. The Horden Till contains erratics and heavy minerals derived from crystalline bedrock sources in the Cheviot Hills and northeast Scotland. Within the Horden Till are numerous sand, clay and gravel-filled canals incised downwards into the diamicton which are attributed to a low-energy, distributed, subglacial canal drainage system. Coupled with hydro-fractures and the boulder pavement, this suggests that a partially decoupled, fast-flowing ice stream deposited the Horden Till. The uphill, landward direction of ice movement indicates that the ice stream was confined in the North Sea Basin, possibly by the presence of Scandinavian Ice.

The classical model of trough mouth fan (TMF) formation was developed in the Polar North Atlantic to explain large submarine fans situated in front of bathymetric troughs that extend across continental shelves to the shelf break. This model emphasizes the delivery of large volumes of subglacial sediment to the termini of ice streams flowing along troughs, and subsequent re-deposition of this glacigenic sediment down the continental slope via debris-flow processes. However, there is considerable variation in terms of the morphology and large-scale sediment architecture of continental slopes in front of palaeo-ice streams. This variability reflects differences in slope gradient, the relative contributions of meltwater sedimentation compared with debris-flow deposition, and sediment supply/geology of the adjacent continental shelf. TMF development is favoured under conditions of a low (

This paper is a sedimentological investigation of Late Devensian glacial deposits from the Solway Lowlands, northwest England, in the central sector of the last British–Irish Ice Sheet. In this region, laminated glaciolacustrine sediments occur, sandwiched between diamictons interpreted as subglacial tills. At one location the laminated sediments are interpreted as varves, and indicate the former presence of a proglacial lake. Correlation of these varves with other laminated sediments indicates that the glacial lake was at least 140 km2 in area and probably much larger. Extensive beds of sand, silt and gravel throughout the Solway Basin associated with the lake demonstrate ice-free conditions over a large area. Based on the number of varves, the lake was in existence for at least 261 years. The stratigraphic sequence of varves bracketed by tills implies a major glacial oscillation prior to the Scottish Re-advance (16.8 cal. ka BP). This oscillation is tentatively correlated with the Gosforth oscillation at c.19.5 cal. ka BP. Subsequent overriding of these glaciolacustrine sediments during a westward-moving re-advance demonstrates rapid ice loss and then gain within the Solway Lowlands from ice-dispersal centres in the Lake District, Pennines and Southern Uplands. It is speculated that the existence of this and other lakes along the northeastern edge of the Irish Sea Basin would have influenced ice-sheet dynamics.

This study reconstructs the depositional environments that accompanied both ice advance and ice retreat of the last British–Irish Ice Sheet in NE England during the Last Glacial Maximum, and proposes three regional ice-flow phases. The Late Devensian (29–22 cal. ka BP) Tyne Gap Ice Stream initially deposited the Blackhall Till Formation during shelf-edge glaciation (Phase I). This subglacial traction till comprises several related facies, including stratified and laminated diamictons, tectonites, and sand and gravel beds deposited both in subglacial canals and in proglacial streams. Eventually, stagnation of the Tyne Gap Ice Stream led to ice-marginal sedimentation in County Durham (Phase II). During the Dimlington Stadial (21 cal. ka BP), the North Sea Lobe advanced towards the coastline of N Norfolk. This resulted initially in sandur deposition (widespread, tabular sand and gravel; the Peterlee Sand and Gravel Formation; Phase II) and ultimately in deposition of the Horden Till Formation (Phase III), a massive subglacial till. As the North Sea Lobe overrode previous formations, it thrusted and stacked sediments in County Durham, and dammed proglacial lakes between the east-coast ice, the Pennine uplands and the remaining Pennine ice. The North Sea Lobe retreated after Heinrich Event 1 (16 ka). This study highlights the complexity of ice flow during the Late Devensian glaciation of NE England, with changing environmental and oceanic conditions forcing a mobile and sensitive ice sheet.