Th. univ.--Géol.--Strasbourg 1, 1990. / La page de titre porte 1992 et la mention de dépôt légal 1993. Bibliogr. p. 113-122.

Research Doctorate - Doctor of Philosophy (PhD) / The northern Central Highlands region of Tasmania extending north from Cradle Mountain to the Middlesex Plains shows evidence of three glacial stages, with the final stage consisting of several ice advance phases. From oldest to youngest these have been named the Middlesex Glaciation, the Sunshine Glaciation and the Cradle Glaciation. Cosmogenic exposure-age dating of boulders and ice-abraded bedrock, radiocarbon dating of post-glacial organic deposits, and relative dating techniques have resulted in assignment of the following ages for the events: Middlesex Glaciation, MIS 10; Sunshine Glaciation, MIS 6 and the Cradle Glaciation having MIS 3 and MIS 2 phases. The Cradle Glaciation correlates with the global Last Glaciation. Exposure-age dating of three of the Cradle Glaciation ice advance phases indicates that the Pencil Pine Phase predates 38.9±4.0 ka, the Dove Phase occurred ca. 29.2±1.4 ka, and the Cradle Valley Phase occurred between >19.7±1.1 – 17.6±1.0 ka. At least two undated retreat/readvance phases followed the Cradle Valley Phase. Deglaciation of the area was probably complete considerably before 11.2 ka. The recognised glacial events decreased in areal extent in each successive advance. Using the 0°C summer mean isotherm as the base for the altitude of the equilibrium line altitude, the regional snowline, regional snowline depression and temperature depression for each of the events were: Middlesex Glaciation, 942 m/1616 m/10.5°C; Sunshine Glaciation, 984 m/1574 m/10.23°C; Pencil Pine Phase, 1010 m/1548 m/10.06°C; Dove Phase, 1050 m/1508 m/9.8°C; and the Cradle Valley Phase, 1060 m/1498 m/9.74°C. The geomorphic evidence and dating of several phases of the Cradle Glaciation indicates a complex history of ice advances for Tasmania during the Last Glaciation.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Earth is characterized by episodes of glaciations and periods of minimal or no ice through geologic time. Using the linear energy balance model (EBM), nonlinear EBM with empirical ice sheet schemes, the general circulation model coupled with an ice sheet model, this study investigates the occurrence and stability of glaciations in geologic time. The simulations since the last glacial maximum (LGM) suggest that the summertime thawline of ice sheets conforms closely to the equatorward edge of the ice sheets and implies the relative stability toward deglaciation. CO2 levels are indispensable in controlling the initiation of ice sheet in the Cretaceous. At low CO2 levels, ice sheets exist in all periods no matter LGM or the last interglacial (LIG) orbital elements; however, at high CO2 levels ice sheets rarely exist. The simulations agree well with recent geological evidence of the hysteresis of glaciations in the Permo-Carboniferous. Gondwanaland reached its glacial maximum when CO2 level was roughly the same or slightly higher than the preindustrial value. With a further increase of CO2, deglaciation dominates and results in an ice free state. Again, if CO2 decreased to the present level, Gondwanaland would be glaciated once more and start a new cycle of glaciation and deglaciation. Simulations from five paleogeography maps in Gondwanaland with a suite of CO2 levels and different orbital elements reveal that paleogeography, CO2 levels and the Milankovitch cycles all contribute to the glaciations of Gondwanaland. This study shows that orbital elements alone are insufficient to account for the evolution of ice sheets. Net radiative forcing caused by greenhouse gases, such as CO2 and solar constant change are the primary drivers to glacial inception or demise. Continental geography, CO2 levels, solar constant change, and the Milankovitch cycles complicate the glacial history of Earth.

Reproduction de : Thèse de doctorat : Dynamique et environnement sédimentaires : Lille 1 : 2004. Reproduction de : Doctoral thesis : Naturwissenschaften : Universität Potsdam : 2004. / Thèse en cotutelle. N° d'ordre (Lille 1) : 3513. Résumé en anglais, en allemand et en français. Titre provenant de la page de titre du document numérisé. Bibliogr. p. 91-101.

Les périodes glaciaires du Pléistocène sont contemporaines de la croissance d’imposantes calottes de glace en Europe, et de la présence du Fleuve Manche qui s’écoulait entre la Grande-Bretagne et la France. Ce fleuve représentait un des plus grands systèmes fluviatiles ayant jamais existé en Europe de l'Ouest. A travers la reconstruction des transferts sédimentaires sur la Marge Nord Gascogne, nous discutons dans ce travail de l’amplitude des oscillations glaciaires et de la puissance du Fleuve Manche au cours des derniers 1,2 millions d’années. Les transferts sédimentaires augmentent significativement lors du développement majeur des calottes glaciaires il y a 900 000 ans et tout particulièrement lors du stade isotopique marin (MIS) 12, il y a 450 000 ans. Durant cette période, la fusion des calottes Britannique et Scandinave en Mer du Nord oblige les eaux d’Europe centrale à s’écouler dans le Golfe de Gascogne au travers du détroit du Pas-de-Calais, dont nous datons l’ouverture il y a 455 000 ans. Cette modification profonde du réseau de drainage européen rend possible une telle configuration lors des périodes glaciaires suivantes, et particulièrement lors des MIS 6 (~150 ka) et MIS 2 (~18 ka). Au cours de ces périodes, les apports sédimentaires sur la Marge Nord Gascogne augmentent brutalement en réponse à la fonte des calottes, la compétence du Fleuve Manche devenant suffisamment importante pour charrier le sédiment issu de l’érosion glaciaire vers le Golfe de Gascogne. Le débit solide minimum du Fleuve Manche est ainsi estimé à 130 Mt an-1 lors de la dernière déglaciation. Plus généralement, nous démontrons, pour la période étudiée, que les transferts sédimentaires sur la Marge Nord Gascogne et le fonctionnement des systèmes turbiditiques Celtique et Armoricain sont très majoritairement contrôlés par le climat. Par ailleurs, la reconnaissance des événements de fonte des calottes européennes tout au long des derniers 1,2 millions d’années a permis, pour la première fois, la corrélation directe de la stratigraphie continentale européenne avec la stratigraphie isotopique marine. / The Pleistocene has been period of fluctuating climate accompanied by prominent sea-level lowstands during the glacial intervals, when massive continental ice sheets extended from mountainous to lowland European areas. The retreat of the shoreline on the extensive present-day shallow continental shelf of the southern part of the British Isles induced the appearance of the ‘Fleuve Manche’ palaeoriver, one of the largest systems that drained the European continent. Sedimentary records from the Bay of Biscay offer an independent record allowing the reconstruction of the freshwater and sediment discharges of the ‘Fleuve Manche’, and the possibility of detecting the imprint of surrounding ice-sheet oscillations and attendant modification of hinterland drainage directions throughout the Pleistocene. For the last 1.2 Ma, the progressive development of extensive Pleistocene ice-sheets over Europe during cold periods favoured sedimentary transfers in the Bay of Biscay, particularly since MIS 12 when the British and Fennoscandian ice sheets merged in the North Sea for the first time, forcing the North Sea fluvial system to flow southwards through the Dover Strait, which opened 455 000 years ago according to our data. From this point onwards, the North Sea drainage, as well as meltwaters that flowed westwards along the southern margin of the Fennoscandian ice-sheet could drain into the Bay of Biscay, as reported through significant terrigenous supplies in the northern Bay of Biscay during the MIS 6 (ca.150 ka) and MIS 2 (ca.18 ka). We assume for example that sediment load delivered to the Bay of Biscay by the ‘Fleuve Manche’ reached 130 M t yr-1 at time of the last melting of the European ice sheet ca. 18 000 years ago. On the whole, we demonstrate, for the studied period, that climate forcing strongly affects the sediment transfer into the northern Bay of Biscay and the turbiditic activity of the Celtic and Armorican turbidite systems. Finally, the recognition of melting events of the European ice sheets throughout the last 1.2 Ma allows, for the first time, the correlation of the European continental glaciation-derived chronology with the marine isotope stratigraphy.

This thesis presents stratigraphic, sedimentological and geochronological results from valley fill and glacial moraines of the Hope-Waiau Valleys in North Canterbury, New Zealand. The findings demonstrate that a substantial portion of the modern valley fill comprises in-situ sedimentary sequences that were deposited during the penultimate glaciation (OIS 6), the last interglacial (OIS 5) and during the mid-late last glacial cycle (OIS 3/2). The sediments survived at low elevations in the valley floor despite overriding by later glacial advances. Sedimentologically, the fill indicates deposition in an ice marginal zone and consists of paraglacial/distal-proglacial aggradation gravels and ice-proximal/marginal-subglacial sediments. Deposition during glacial advance phases was characterized by the sedimentation of outwash gravels and small push moraines while glacial retreat phases are dominated by glaciolacustrine deposits which are frequently interbedded with debris flow diamictons. The overall depositional arrangement indicates that glacial retreat from the lower valley portion occurred via large scale ice stagnation. Results from infra-red stimulated luminescence (IRSL) dating gives evidence for five large aggradation and degradation phases in the Hope-Waiau Valleys over the last 200 ka. Combined with surface exposure dating (SED) of moraines the geochronological results indicate that glacial advances during OIS 6 were substantially larger in both ice extent and ice volume than during OIS 4-2. The last glacial maximum (LGM) ice advance occurred prior to 20.5 ka and glacial retreat from extended ice positions began by ~18 ka BP. A late glacial re-advance (Lewis Pass advance) occurred at ~13 ka BP and is probably associated with a regional cooling event correlated to the Antarctic Cold Reversal (ACR). The findings from the Hope-Waiau Valleys were integrated into a model for glaciations in the Southern Alps which uses data from a snow mass balance model to analyse the sensitivity of glacial accumulation to temperature forcing. Model results indicate that in the central hyperhumid sector of the Southern Alps ice would expand rapidly with minor cooling (2-4℃) suggesting that full glaciation could be generated with little thermal forcing. Some Quaternary glacial advances in the Southern Alps may have been triggered by regional climate phenomena (e.g. changes in ENSO mode) rather than requiring a thermal trigger from the Northern Hemisphere.

This thesis develops a better knowledge of the extent and timing of glaciations in southern Argentina throughout the Quaternary. It provides a detailed understanding of successive major glacial outlet lobes in the Lago Pueyrredón valley. The glacial and glaciofluvial deposits in the valley, as elsewhere in the region, are extremely well-preserved and reflect punctuated glacial advances between ~ 1.1 Ma and ~ 17 ka. Several intermediate glaciations are undated, constrained by the limited time frame of radiocarbon age dating, the limited potential volcanic sites for K-Ar or 40Ar/39Ar age dating, and erosion and exhumation problems associated with cosmogenic-nuclide surface exposure ages on moraines. This thesis provides a new chronology for the mid-Quaternary glaciations based on methodological advances in cosmogenic-nuclide surface exposure age dating. This is done by deriving ages from glacial outwash terrace sediment and demonstrating their reliability. The work shows that for younger (i.e., last glacial) moraines, well-constrained ages can be derived from the common-practice of dating large boulders on the moraine surface. However, on older moraines, the ages so-derived become considerably scattered. This is interpreted to be caused primarily by boulder exhumation as a consequence of moraine erosion, resulting in shorter residence of some boulders at the surface relative to the moraine formation date. By contrast, glacial outwash surfaces in this area, if carefully chosen, can be shown to have undergone little aggradation or erosion, and thus have had long and consistent surface exposure since formation. Provided these surfaces can be stratigraphically linked with the glacial limits, they can provide good surface exposure ages. This has been convincingly confirmed in one location by a sequence of ages obtained from a 10Be concentration depth-profile which demonstrate the surface stability and lack of inherited nuclides. Using these methods, cosmogenic 10Be and 26Al surface exposure ages indicate successive major advances occurred at ~ 1.2 Ma, ~ 600 ka, ~ 260 ka and ~27 – 17.5 ka. These are correlated with global marine and ice core records.

This thesis presents stratigraphic, sedimentological and geochronological results from valley fill and glacial moraines of the Hope-Waiau Valleys in North Canterbury, New Zealand. The findings demonstrate that a substantial portion of the modern valley fill comprises in-situ sedimentary sequences that were deposited during the penultimate glaciation (OIS 6), the last interglacial (OIS 5) and during the mid-late last glacial cycle (OIS 3/2). The sediments survived at low elevations in the valley floor despite overriding by later glacial advances. Sedimentologically, the fill indicates deposition in an ice marginal zone and consists of paraglacial/distal-proglacial aggradation gravels and ice-proximal/marginal-subglacial sediments. Deposition during glacial advance phases was characterized by the sedimentation of outwash gravels and small push moraines while glacial retreat phases are dominated by glaciolacustrine deposits which are frequently interbedded with debris flow diamictons. The overall depositional arrangement indicates that glacial retreat from the lower valley portion occurred via large scale ice stagnation. Results from infra-red stimulated luminescence (IRSL) dating gives evidence for five large aggradation and degradation phases in the Hope-Waiau Valleys over the last 200 ka. Combined with surface exposure dating (SED) of moraines the geochronological results indicate that glacial advances during OIS 6 were substantially larger in both ice extent and ice volume than during OIS 4-2. The last glacial maximum (LGM) ice advance occurred prior to 20.5 ka and glacial retreat from extended ice positions began by ~18 ka BP. A late glacial re-advance (Lewis Pass advance) occurred at ~13 ka BP and is probably associated with a regional cooling event correlated to the Antarctic Cold Reversal (ACR). The findings from the Hope-Waiau Valleys were integrated into a model for glaciations in the Southern Alps which uses data from a snow mass balance model to analyse the sensitivity of glacial accumulation to temperature forcing. Model results indicate that in the central hyperhumid sector of the Southern Alps ice would expand rapidly with minor cooling (2-4℃) suggesting that full glaciation could be generated with little thermal forcing. Some Quaternary glacial advances in the Southern Alps may have been triggered by regional climate phenomena (e.g. changes in ENSO mode) rather than requiring a thermal trigger from the Northern Hemisphere.