The climate of the Wester Ross region of NW Scotland is particularly sensitive to fluctuations in the strength and latitude of the North Atlantic Gulf Stream. This was particularly apparent during the last deglaciation (14.7-12.9 ka), when overall climatic amelioration was interrupted by periods of cooling, the most significant being a 1.2 ka return to glacial conditions during the Younger Dryas (12.9-11.5 ka). Glacial readvances during these cooling episodes left behind numerous geomorphological features, which have been mapped and interpreted through a variety of methods, including fieldwork observations, aerial photography and digital elevation models, to form a detailed reconstruction of the style and timing of deglaciation. These methods were augmented by the study of 3D digital models, produced by combining 5cm resolution, Light Detection and Ranging (LiDAR) scans with colour photography, leading to the production of a detailed geomorphological map of a cirque formation in Torridon, Wester Ross, which was covered by an ice-sheet at the Last Glacial Maximum, and experienced localised ice flow during subsequent deglaciation and readvances. Six statistically comparable cosmogenic 10Be bedrock exposure ages give a Younger Dryas age for sites in Torridon and Applecross (Wester Ross), and have also been used to constrain the vertical extent of these ice fields. Reconstructions of these ice bodies revealed that the Torridon ice field (mean ELA, 482m) covered ~100km2, over twice the surface area covered by the Applecross ice field (~43km2). This could have resulted from the survival of ice in Torridon prior to the onset of the Younger Dryas cooling, and is tentativelty supported by pre-Younger Dryas cosmogenic 10Be exposure ages from this study and previous studies, which imply that ice existed close to the Wester Ross coastline and within central Torridon between 14-13ka. The Applecross ice field mean ELA (361m) was lowered by the presence of independent glaciers, which formed in low-lying troughs as snow was efficiently transferred to the NE by prevailing SW winds. Using empirical values from a global dataset, average annual Younger Dryas palaeoprecipitation values for the Torridon and Applecross ELAs are 2010 ± 266 and 2312 ± 534 mm a-1 respectively, suggesting a wetter climate than today. Palaeoprecipitation calculated using equations based on a climate model of NW Scotland, yield lower values between 1005 ± 67 mm a-1 and 1758 ± 118 mm a-1 for the Torridon ELA and 1205 ± 233 mm a-1 to 2109 ± 407 mm a-1 for the Applecross ELA, perhaps a more reliable estimate which reflect enhanced continentaility, promoted by the formation of sea ice on the NE Atlantic seaboard during the Younger Dryas.Despite the rapid warming observed in palaeotemperature proxies, studies of glacial geomorphology and basal shear stress suggest that initial deglaciation was slow, oscillatory and warm-based, leading to the formation of prominent retreat moraines in the lower valleys. This prolonged transition can be related to the northward migration of sea ice and the gradual reintroduction of a Gulf Stream-dominated maritime climate. Ice remaining in the central area down-wasted in-situ as the regional ELA increased, creating hummocky landscape. Finally, cosmogenic 10Be exposure ages indicate that glaciers (probably characerised by a polythermal regime) retreated into the high north-facing corries at approximately 11.8ka, depositing a series of flutes.

No description available.

No description available.

The Neoproterozoic is one of the most enigmatic periods in Earth history. In the juxtaposition of glacial and tropical deposits the sedimentary record provides evidence for extreme climate change. Various models have tried to explain these apparent contradictions. One of the most popular models is the Snowball Earth Hypothesis which envisages periods of global glaciations. All climatic models are dependent on palaeogeography which as yet remains poorly constrained for the Neoproterozoic. This thesis presents a multidisciplinary study of two Neoproterozoic sedimentary basins on the Congo and West Africa cratons including radiometric dating of glacial deposits themselves. In the West Congo Belt, western Congo Craton, a new U-Pb baddeleyite age for the Lower Diamictite provides the first high quality direct age for the older of two glacial intervals. This age is significantly different from previously dated glaciogenic deposits on the Congo Craton. This result strongly suggests that the mid-Cryogenian was a period during which several local glaciations occurred, none of which were global. While the palaeomagnetic results from carbonates around the younger glacial interval are probably remagnetised, detrital zircon and chemostratigraphic results allow correlation with numerous late-Cryogenian glaciogenic deposits worldwide and a Snowball Earth scenario is favoured here. In the Adrar Sub-Basin of the vast Taoudéni Basin, West Africa, the terrigenous Jbeliat glacial horizon has been studied in great detail. Detrital zircon geochronology reveals large changes in provenance through this glacial unit with implications for sedimentological approaches and techniques for provenance characterisations based on one sample alone. Together with recently published U-Pb data these results constrain the age of the Jbeliat Group to a narrow window providing vital geochronological information for this younger glacial event. Combining provenance geochemistry, chemostratigraphy and U-Pb dating has greatly improved our understanding of two of the largest Neoproterozoic sedimentary basins. The dominance of Mesoproterozoic detrital material, for which no source has been reported near either of the field areas, has consequences for the proximity of other cratons at the time of deposition, prior to the final amalgamation of Gondwana.

This thesis presents the findings of a combined geomorphological, sedimentological and geochronological investigation into the glacial history of the Clearwater Basin, Mid Canterbury, New Zealand. The study demonstrates that a thick wedge of glacial and paraglacial sediments are preserved in the valley. These are >100m thick and preserve evidence of at least 3 glacial phases (>180ka). The study presents a new and detailed geomorphology map for the Clearwater valley and adjacent areas and has added 17 new recessional positions to the local glacial record. Surface Exposure Dating (SED) has been used to directly date the moraines of the Clearwater Basin providing the first detailed chronology for glacial moraine in this area. In total 31 cosmogenic ages from 9 separate moraines are presented. The results demonstrate that the LGM advance is the Trinity moraine of Mabin (1980) and not the Hakatere moraine as previously assumed and that the LGM was achieved at or about 23ka. The Clearwater glacier receded up valley between 23 and 13ka with some indication of accelerated retreat after c.16ka. The correlation to the adjacent Lake Heron Valley is also revised.

The submitted diploma thesis deals with relative dating of the youngest glacigenic sediments (moraines) in the upper parts of some selected valleys in the High Tatra Mountains. These moraines were stabilized after the last cold events of the last glaciation cycle. The Schmidt hammer (SH) test was used for the assessment of their relative age. This method is based on the assumption that there is a mutual relation between the degree of weathering of a tested surface and the duration of its exposure. Information about the degree of weathering is expressed by the Rebound (R) value. The measurements were taken on fifteen moraines in four valleys in the High Tatra Mountains (Mengusovská, Velká Studená, Malá Studená and Litvorova valley). A large statistical population of measurements obtained from moraine surfaces were used to analyse the variability of R values means in the same lithology. The moraines were divided on the base of SH measurements into two groups of different age. R value means and standard deviation for these groups (SK_1: R=53,5±1,2 a SK_2: R=58,6±1,5) are significantly statistically different. The results of the weathering indexes were used for the reconstruction of the pattern of deglaciation in selected upper parts of valleys (cirques). Key words: relative dating, the Schmidt Hammer,...

Data from new subsurface studies, lithologic analyses, radiocarbon dating, and geologic mapping demonstrate that an early middle Wisconsinan (MIS 3) to late Wisconsonan (MIS2) till sheet is more widespread in northcentral Iowa than previously assumed. This till had been mapped to the west of and beneath the late Wisconsinan (MIS 2) Des Moines Lobe (DML); this thesis research has shown that the boundary of that till sheet extends 40 to 50 km east of the DML margin. Sediments deposited by the MIS 3 glacier are termed the Sheldon Creek Formation; they share many lithologic properties with DML Dows Formation deposits. Some of these shared properties, such as clasts of Pierre Shale, suggest a similar northwesterly provenance and glacial flow from the Keewatin Dome of the Laurentide Ice Sheet during both glaciations. Radiocarbon ages of organic materials within and beneath the Sheldon Creek Formation, as well as stratigraphic relationships in cores and outcrops, suggest that the unit accumulated during two distinct advances, herein named the Ft. Dodge Advance (ca. 46-40 ka) and the Lehigh Advance (ca. 34-29 ka). The presence of ice in Iowa before the regional Last Glacial Maximum has important implications for modeling buildup of the Laurentide Ice Sheet (LIS) and understanding the regional variability of ice sheet extent during the last glacial period. Existing models the LIS buildup are challenged by the pre-MIS 2 chronology reported here, which puts the ice sheet much farther south during MIS 3b than had previously been reported. This points to a much earlier buildup of the Keewatin Dome than previously assumed. The timing of the Sheldon Creek advances appear to coincide with Heinrich events 3 and 5 in the North Atlantic, indicating that both the Keewatin and Laurentian Domes of the ice sheet were large at this time. Further work needs to be done to determine if the MIS 3b and early MIS 2 Sheldon Creek Formation deposits in Iowa are unique, or if there are other unrecognized deposits from these time periods.

During the Quaternary period, cyclic glaciations have occurred over a global scale as the result of a climatic variability that affected the Earth's atmospheric, oceanic and glacial systems. Quaternary glaciations and their associated dramatic climatic conditions, such as kilometers-thick ice sheet formation and permafrost migration, are suspected to have had a large impact on the groundwater flow system over the entire North American continent. Because of the myriad of complex flow-related processes involved during a glaciation period, numerical models have become powerful tools to examine groundwater flow system evolution in this context. In this study, a series of key processes pertaining to coupled groundwater flow and glaciation modelling, such as density-dependent (i.e., brine) flow, hydromechanical loading, subglacial infiltration, isostasy, sea-level change and permafrost development, are included in the numerical model HydroGeoSphere to simulate groundwater flow over the Canadian landscape during the Wisconsinian glaciation (~ -120 kyr to present). The primary objective is to demonstrate the immense impact caused by glacial advances and retreats during the Wisconsinian glaciation on the dynamical evolution of groundwater flow systems over the Canadian landscape, including surface/subsurface water exchanges (i.e., recharge and discharge fluxes) both in the subglacial and the periglacial environments. The major findings of this study are that subglacial meltwater infiltration into the subsurface dominates when the ice sheet is growing and, conversely, groundwater exfiltrates during ice sheet regression. This conclusion, which seems to be opposite to the classical hydromechanical loading theory, is a consequence of the interaction between the subglacial boundary conditions and the elastic properties of the rocks. Subglacial infiltration rates during ice sheet progression can reach up to three orders of magnitude higher than the infiltration rate into the periglacial environment and the current recharge rate into the Canadian Shield. The impact of the ice sheet on groundwater flow and the brine distribution was dramatic. Hydraulic heads below the ice sheet increase by up to three thousand meters at land surface and up to 1.5 km into the ground. At present time, large over-pressurized zones occur at depth because there has been insufficient time to enable dissipation to their original values. Based on the hydraulic head and solute concentration distribution after the last glacial cycle, it can be shown that the system did not recover to its initial conditions, and that it is still recovering from the last glacial perturbation. The permafrost has the effect of restraining large areas of the subglacial and periglacial environment from surface/subsurface water interaction; the subglacial permafrost appears along with a cold-based ice sheet, which prevents subglacial meltwater production. The occurrence of a shallow trapped pressure zone below the permafrost after the glacial cycle highlights the critical importance of permafrost on the recovery of the flow system after a glacial cycle. As a final contribution, the mean groundwater age across the Canadian landscape at the last interglacial (LIG) and throughout the last glacial cycle was computed. Groundwater age is defined as the time elapsed since the water infiltrated in a recharge zone; the mean groundwater age is the mean age of all the particles of water that would be measured in a sample of water. It was found that at LIG, the mean groundwater ages span a large range of values from zero to 42 Myr. Forty-two Myr old groundwater was calculated at depth where there is little groundwater flow and where a mass of stagnant groundwater exists due to high brine concentrations. During the glacial period, old groundwater below the ice sheet mixes with young subglacial meltwater that infiltrates into the ground and the resulting mean groundwater age is younger. The mixing below the ice sheet occurs at great depth, and locations where the mean groundwater age was older than 1 Myr reaches mean age values between 10 kyr and 100 kyr.

During the Quaternary period, cyclic glaciations have occurred over a global scale as the result of a climatic variability that affected the Earth's atmospheric, oceanic and glacial systems. Quaternary glaciations and their associated dramatic climatic conditions, such as kilometers-thick ice sheet formation and permafrost migration, are suspected to have had a large impact on the groundwater flow system over the entire North American continent. Because of the myriad of complex flow-related processes involved during a glaciation period, numerical models have become powerful tools to examine groundwater flow system evolution in this context. In this study, a series of key processes pertaining to coupled groundwater flow and glaciation modelling, such as density-dependent (i.e., brine) flow, hydromechanical loading, subglacial infiltration, isostasy, sea-level change and permafrost development, are included in the numerical model HydroGeoSphere to simulate groundwater flow over the Canadian landscape during the Wisconsinian glaciation (~ -120 kyr to present). The primary objective is to demonstrate the immense impact caused by glacial advances and retreats during the Wisconsinian glaciation on the dynamical evolution of groundwater flow systems over the Canadian landscape, including surface/subsurface water exchanges (i.e., recharge and discharge fluxes) both in the subglacial and the periglacial environments. The major findings of this study are that subglacial meltwater infiltration into the subsurface dominates when the ice sheet is growing and, conversely, groundwater exfiltrates during ice sheet regression. This conclusion, which seems to be opposite to the classical hydromechanical loading theory, is a consequence of the interaction between the subglacial boundary conditions and the elastic properties of the rocks. Subglacial infiltration rates during ice sheet progression can reach up to three orders of magnitude higher than the infiltration rate into the periglacial environment and the current recharge rate into the Canadian Shield. The impact of the ice sheet on groundwater flow and the brine distribution was dramatic. Hydraulic heads below the ice sheet increase by up to three thousand meters at land surface and up to 1.5 km into the ground. At present time, large over-pressurized zones occur at depth because there has been insufficient time to enable dissipation to their original values. Based on the hydraulic head and solute concentration distribution after the last glacial cycle, it can be shown that the system did not recover to its initial conditions, and that it is still recovering from the last glacial perturbation. The permafrost has the effect of restraining large areas of the subglacial and periglacial environment from surface/subsurface water interaction; the subglacial permafrost appears along with a cold-based ice sheet, which prevents subglacial meltwater production. The occurrence of a shallow trapped pressure zone below the permafrost after the glacial cycle highlights the critical importance of permafrost on the recovery of the flow system after a glacial cycle. As a final contribution, the mean groundwater age across the Canadian landscape at the last interglacial (LIG) and throughout the last glacial cycle was computed. Groundwater age is defined as the time elapsed since the water infiltrated in a recharge zone; the mean groundwater age is the mean age of all the particles of water that would be measured in a sample of water. It was found that at LIG, the mean groundwater ages span a large range of values from zero to 42 Myr. Forty-two Myr old groundwater was calculated at depth where there is little groundwater flow and where a mass of stagnant groundwater exists due to high brine concentrations. During the glacial period, old groundwater below the ice sheet mixes with young subglacial meltwater that infiltrates into the ground and the resulting mean groundwater age is younger. The mixing below the ice sheet occurs at great depth, and locations where the mean groundwater age was older than 1 Myr reaches mean age values between 10 kyr and 100 kyr.

Using GIS-based tools and a review of the relevant geological and climatic literature, I attempt to identify the key implications of Quaternary glacial cycles for drainage evolution in eastern Patagonia. In doing so, the stage is set for the proper integration of existing biogeographic and phylogeographic ideas to develop a suite of inferences aimed at elucidating how these processes influenced aquatic biodiversity of Patagonian Argentina. A primary finding of this research is that the southern mainland and/or Tierra del Fuego served as an important cryptic refuge for cold-adapted species, including aquatic taxa. At least one additional aquatic refuge is likely to have existed in either central or northern Patagonia. The low position of the Atlantic shoreline during glacial periods also revealed a much larger and inter-connected drainage network in southern Patagonia. During sea-levels stands below 100m, two new drainage coalescence points on the exposed continental shelf can be recognized among the Chico/Santa Cruz, Coyle and Gallegos river basins and between the Grande and Fuego rivers. Enhanced hydrological discharge during the deglaciation period of Late-Quaternary cycles is expected to have facilitated extensive inter-drainage connections within each of the northern and southern regions of eastern Patagonia via proglacial lake and/or stream coalescence. A large proglacial lake in the Nahuel Huapi Lake region is also recognized as the most likely temporary gateway for aquatic organisms to disperse between the Neuquen and Northern Patagonian Tablelands. I also recognize climate-induced drainage reversals as a bidirectional mechanism of trans-Andean dispersal and an important factor in determining the biogeography of widespread aquatic organisms in Patagonia.