Through the measurement of the concentrations of the in situ cosmogenic nuclides 1°Be and 26A1 within rock surfaces, this thesis has attempted to solve previously intractable problems regarding the timing and magnitude of glaciation during the last glacial cycle in the vicinity of the Drake Passage. In southernmost Patagonia we have been able to constrain the timing of two major advances of the formerly expanded Patagonian Ice Sheet during the last glacial interglacial transition. In the past these have been in question due to the paucity of radiocarbon dates, in the extremely and conditions prevailing to the east of the southern-most Andes. The timing of deglaciation over 16° of latitude appears to be synchronous, although the magnitude of glaciation differed markedly from latitude to latitude. In southernmost Patagonia maximum ice extent was achieved before 26 ka BP, and deglaciation occurred rapidly at around 17 ka Bp. This is indistinguishable from that of the last glacial period in the Northern Hemisphere. This is interesting as it at a time when insolation was rising to its maximum in the southern hemisphere. The similarity of glacial chronologies from mid-latitudes in both hemispheres indicate that global atmospheric signaling is a major driving mechanism of climate. Results from Antarctica indicate a much more complex picture, with the Antarctic Peninsula and the Shackleton Range Mountains producing very different patterns of deglaciation. These data suggest that glaciation of the Antarctic Peninsula has been forced predominately by eustatic sea level fluctuations, with a complex spread of ages, suggesting ice surface thinning at times of rapid sea level rise. The pattern of deglaciation is very different in the Shackleton Mountains of Antarctica where Quaternary glacial fluctuations have been characterised by extreme stability, with no evidence of substantial ice thickening suggested by some hypotheses. The concentrations of radionuclides demonstrate that these summits have not been covered by ice for significant periods during the Quaternary. The implication is that this periphery of the East Antarctic Ice Sheet has not thickened by more than 400 m in the last 3 million years. Although these are only preliminary results, they place important constraints on glacial modelling studies and research regarding ice thickening of the Filchner Ice Shelf during glacial maxima. In turn these data have implications for ice-sheet controls of the global seawater budget during the last glacial interglacial cycle.

No description available.

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No description available.

This thesis examines how microstructures in glaciogenic sediments reflect the processes forming them, and how these microstructures then affect the conditions around them, through a series of field studies, laboratory tests, models, and statistical analyses. Following literature reviews, a deformational chronology is developed for diamictons at Criccieth, North Wales, and their microstructures are used to indicate the stress, hydraulic, and environmental changes the materials have undergone. Microstructures of the lowest diamict indicate clast lodgement. The processes reflected in the microstructures of this lowest diamict are built into a quantitative model that estimates its residual strength (20 - 50 kPa) and the ice velocity during lodgement (20 - 50 m a-1). The response of sediment to glacial stress is further examined by triaxial testing of diamict from Yorkshire, and the subsequent examination of its micromorphology. Shears in the material are disrupted by clasts, and this may be responsible for work hardening seen during the tests. Fabric compression, and the development of immobilised shears or hydraulic fractures buffer pore fluid pressure to ~470 kPa. The information from previous chapters is then used to analyse other material from the Yorkshire coast. This analysis confirms the presence in the area of meltout tills that have undergone low strain, as well as providing evidence for the decoupling of the ice and sediment in this region, and the nature of drainage systems within and above the diamicts during glaciation. Overall this thesis details the processes forming three ‘classic’ microstructures found in glacial sediments; omnisepic fabrics, lattisepic fabrics, and melanges, and provides evidence for the processes involved in forming diamict pebbles and skelsepic fabrics. In addition this thesis details how such structures reflect coupling and decoupling processes between glaciers and their beds, and examines the manner in which microstructures affect the response of a subglacial sediment body to stress and hydraulic conditions.

The aim of the research reported in this thesis is to establish the characteristics of paraglacial modification of drift-mantled hillslopes in glaciated upland valleys in Norway and Scotland. Debris flow represents the principal agent of paraglacial sediment reworking, though snow avalanches and slopewash are locally important. Paraglacial hillslope modification is most widespread in areas of thick drift where initial slopes exceed c. 30°, void ratio exceeds c. 0.35, and water input is focused both spatially and temporally. Paraglacially-reworked sediments preserve most of the characteristics of the parent tills, but differ in terms of preferred clast orientation and structural and lithofacies characteristics. Stratigraphic relations between tills and reworked sediments imply cyclic alternation of glacial and paraglacial sediment transport. Paraglacial slope adjustment follows a sequence involving (1) rapid gully incision; (2) widening of gullies, and accumulation of debris cones at the slope foot; (3) reduction and destruction of inter-gully divides, and formation of a slope-foot apron of coalescing cones; (4) extensive exposure of bedrock at the crest of the slope, resulting in sediment exhaustion and progressive stabilisation. Slope profiles tend to converge on a maximum gradient of c. 28° and a concavity index of c. 0.22. At the most active sites, 2-4 m of gully lowering has occurred within decades of deglaciation, implying minimum erosion rates averaging c. 90 mm yr ⁻¹. In Scotland delayed or renewed reworking of drift-mantled slopes has occurred several millennia after deglaciation. Radiocarbon dating of buried palaeosols indicates intermittent drift reworking by debris flows throughout the past 6.5 ka, with some evidence for accelerated activity at c. 2.7-1.7 cal ka BP and after c. 0.7 cal ka BP. Three-dimensional conceptual models are developed to describe the sequence of both immediate and delayed or renewed paraglacial hillslope modification, and the landforms and sediment associations characteristic (and diagnostic) of paraglaciallandsystems in passive continental margins.

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No description available.

No description available.

No description available.