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In low relief Precambrian gneiss terrain in eastern Sweden, abraded bedrock surfaces were ripped apart by the Fennoscandian Ice Sheet. The resultant boulder spreads are covers of large, angular boulders, many with glacial transport distances of 1–100 m. Boulder spreads occur alongside partly disintegrated roches moutonnées and associated fracture caves, and are associated with disrupted bedrock, which shows extensive fracture dilation in the near surface. These features are distributed in ice-flow parallel belts up to 10 km wide and extend over distances of >500 km. Our hypothesis is that the assemblage results from (1) hydraulic jacking and bedrock disruption, (2) subglacial ripping and (3) displacement, transport and final deposition of boulders. Soft sediment fills indicate jacking and dilation of pre-existing bedrock fractures by groundwater overpressure below the ice sheet. Overpressure reduces frictional resistance along fractures. Where ice traction overcomes this resistance, the rock mass strength is exceeded, resulting in disintegration of rock surfaces and ripping apart into separate blocks. Further movement and deposition create boulder spreads and moraines. Short boulder transport distances and high angularity indicate that glacial ripping operated late in the last deglaciation. The depths of rock mobilized in boulder spreads are estimated as 1–4 m. This compares with 0.6–1.6 m depths of erosion during the last glaciation derived from cosmogenic nuclide inventories of samples from bedrock surfaces without evidence of disruption. Glacially disrupted and ripped bedrock is also made ready for removal by future ice sheets. Hence glacial ripping is a highly effective process of glacial erosion. [ABSTRACT FROM AUTHOR]

ABSTRACT We present a review of over 175 years of research into the Middle to Late Devensian (Weichselian) glaciation of NE Scotland based crucially on both its lithostratigraphic and geomorphic records. The location of the region, and surrounding seabed, makes this unusually detailed record significant for deciphering the former interactions and dynamics of Scottish and Scandinavian ice within the North Sea Basin (NSB), which continue to be controversial. A 12-stage event stratigraphy is proposed based on a parsimonious interpretation of stratigraphic relationships, till lithology and regional clast fabrics, striae, subglacial bedforms, ice-marginal features and published geochronometry at critical sites. The record of regional glaciation supports converging evidence that the north-eastern quadrant of the last British and Irish Ice Sheet reached its maximum spatial extent in the late Middle to early Late Devensian and later re-expanded following widespread internal glacial reorganizations, marine transgression and partial retreat from the central NSB. Retreat was interrupted by several glacial readvances of limited extent. Field-captured data help to identify important events that are not clearly resolved from remote sensing alone, particularly regarding growth phases of the last glaciation. [ABSTRACT FROM AUTHOR]

The question of whether the Shetland Islands were covered by an ice cap or by an ice sheet during the last glacial cycle (40-10 ka) remains unresolved. This paper addresses this problem using existing and new data on glacial erratic carry, striae, glacial lineaments and roche moutonnée asymmetry. Its focus is on eastern Shetland, where ice-cap and ice-sheet glaciation would lead to opposed ice-flow directions, towards and away from the North Sea. Evidence cited in support of ice-sheet glaciation of Shetland is questioned. The primary survey of striae correctly identified striae orientation but the direction of ice flow from striae on eastern Shetland was misinterpreted: it was not from, but towards the North Sea. Glacial lineaments interpolated to cross the spine of Shetland instead are discontinuous and diverge away from an axial ice-shed zone that lacks lineaments. Glacitectonic structures cited recently as evidence for westward flow of an ice sheet across eastern Shetland have been partly misinterpreted and other ice-flow indicators in the vicinity of key sites indicate former eastward ice flow towards the North Sea. Westward carry of erratics over short distances in N and S Shetland may be partly accounted for by shifts in ice sheds during ice-cap deglaciation. Collectively, the evidence for movement of the Fennoscandian ice sheet across Shetland is weak. Any ice-sheet incursion over Shetland occurred before the last glacial cycle. The cleansed ice-flow directional data for Shetland show a simple pattern of divergent ice flow from an axial ice-shed zone beneath an ice cap. The deglaciation sequence for the ice cap is evident from sea-bed moraine systems. The Shetland ice cap at the Last Glacial Maximum was substantial, attaining a thickness of 1 km and a diameter of >160 km. The ice cap was of sufficient size to restrain the Fennoscandian ice sheet on the western edge of the Norwegian Channel and to divert the British ice sheet over Orkney. Glacial landscapes on Shetland indicate that ice-cap glaciation has been the dominant mode of glaciation during the Pleistocene. [ABSTRACT FROM AUTHOR]

We investigate the long-term geomorphological evolution of the inselberg plains on the glaciated northern Fennoscandian shield. The shield surfacehas been largely stripped of pre-Quaternary correlative sediments and saprolites by non-glacial and glacial erosion, which make investigations of pre-Quaternary landscape development a challenge. The relief of the study area, covering 33,000 km2 in the centre of the shield in northern Sweden, includes an abundance of inselbergs that provide the basis for the study. We examine the relief of the inselberg plains, integrated with glacial-geomorphologic features, geology, and weathering remnants, by using GIS-analysis and fieldwork. Several key areas are used to demonstrate the impact of glaciations on the large-scale relief, and the influence of geology, structure and deep weathering on relief formation. Glacial erosion had only a minor impact on the large-scale bedrock morphology of northern Sweden. Based on excavations and observations in the Parkajoki area, an area largely preserved under cold-based ice during Quaternary glaciations, we infer that grus weathering, resulting in saprolite covers of up to 10-20 m thickness, occurred in the Neogene. However, inselbergs are considerably higher than that, and must therefore be the result of older deep weathering and erosional events. Narrow fracture zones associated with deep kaolins found in northern Fennoscandia may represent the roots of older generations of deep weathering covers but their age and formation is yet unclear. The geology of the area has greatly influenced the present surface relief. The positions and footprints of the inselbergs are often closely controlled by bedrock type and fracturing. Granite inselbergs generally have dome forms where dome shape and slopes are determined by joint patterns. Steps between palaeosurfaces locally coincide with lithological boundaries and major faults. These links indicate the fundamental importance of etch processes in shaping the relief through multiple cycles of deep weathering and stripping. Palaeosurfaces have been extended and lowered through time, with isolation of small inselbergs during erosion of higher palaeosurfaces. The timescales for relief generation remain uncertain and there is a pressing need to understand the significance of and to date the sediments, saprolites and weathered ore bodies that rest on the surface of the northern Fennoscandian shield. [ABSTRACT FROM AUTHOR]

Abstract: The occurrence of tors within glaciated regions has been widely cited as evidence for the preservation of relic pre-Quaternary landscapes beneath protective covers of non-erosive dry-based ice. Here, we test for the preservation of pre-Quaternary landscapes with cosmogenic surface exposure dating of tors. Numerous granite tors are present on summit plateaus in the Cairngorm Mountains of Scotland where they were covered by local ice caps many times during the Pleistocene. Cosmogenic 10Be and 26Al data together with geomorphic relationships reveal that these landforms are more dynamic and younger than previously suspected. Many Cairngorm tors have been bulldozed and toppled along horizontal joints by ice motion, leaving event surfaces on tor remnants and erratics that can be dated with cosmogenic nuclides. As the surfaces have been subject to episodic burial by ice, an exposure model based upon ice and marine sediment core proxies for local glacial cover is necessary to interpret the cosmogenic nuclide data. Exposure ages and weathering characteristics of tors are closely correlated. Glacially modified tors and boulder erratics with slightly weathered surfaces have 10Be exposure ages of about 15 to 43 ka. Nuclide inheritance is present in many of these surfaces. Correction for inheritance indicates that the eastern Cairngorms were deglaciated at 15.6±0.9 ka. Glacially modified tors with moderate to advanced weathering features have 10Be exposure ages of 19 to 92 ka. These surfaces were only slightly modified during the last glacial cycle and gained much of their exposure during the interstadial of marine Oxygen Isotope Stage 5 or earlier. Tors lacking evidence of glacial modification and exhibiting advanced weathering have 10Be exposure ages between 52 and 297 ka. Nuclide concentrations in these surfaces are probably controlled by bedrock erosion rates instead of discrete glacial events. Maximum erosion rates estimated from 10Be range from 2.8 to 12.0 mm/ka, with an error weighted mean of 4.1±0.2 mm/ka. Three of these surfaces yield model exposure-plus-burial ages of 295−71 +84, 520−141 +178, and 626−85 +102 ka. A vertical cosmogenic nuclide profile across the oldest sampled tor indicates a long-term emergence rate of 31±2 mm/ka. These findings show that dry-based ice caps are capable of substantially eroding tors by entraining blocks previously detached by weathering processes. Bedrock surfaces and erratic boulders in such settings are likely to have nuclide inheritance and may yield erroneous (too old) exposure ages. While many Cairngorm tors have survived multiple glacial cycles, rates of regolith stripping and bedrock erosion are too high to permit the widespread preservation of pre-Quaternary rock surfaces. [Copyright &y& Elsevier]