Glaciation is considered one of the main natural processes that can have a significant impact on the long term performance of DGRs. The northern part of the American continent has been subjected to a series of strong glaciation and deglaciation events over the past million years. Glacial cycles cause loading and unloading, temperature changes and hydraulic head changes at the ground surface. These changes can be classified as transient boundary conditions. It is widely accepted that the periodic pattern of past glacial cycles during the Late Quaternary period are resultant of the Earth’s orbital geometry changes that is expected to continue in the future. Therefore, from the safety perspective of DGRs, such probable events need to be taken into account. The objective of this thesis is to develop a numerical model to investigate the thermo-hydro-mechanical-chemical (THMC) coupled processes that have resulted from long term past and future climate changes and glaciation cycles on a proposed DGR in sedimentary rocks in southern Ontario. The first application is done on a large geological cross section that includes the entire Michigan basin by using a hydro-mechanical (HM) coupled process. The results are compared with field data of anomalous pore water pressures from deep boreholes in sedimentary rocks of southern Ontario. In this work. The modeling results seem to support the hypothesis that at least the underpressures in the Ordovician formation could be partially attributed to past glaciation. The second application is made on site conditions by using the THMC model. The results for the pore water pressure, tracer profiles, permafrost depth and effective stress profile are compared with the available field data, the results show that the solute transport in the natural limestone and shale barrier formations is controlled by diffusion, which provide evidence that the main mechanism of transport at depth is diffusion-dominant. The third application is made on site conditions to determine the effect of underground changes in DGRs due to DGR construction. The results show that future glaciation loads will induce larger increases in effective stresses on the shaft. Furthermore, it is found that hypothetical nuclide transport in a failed shaft can be controlled by diffusion and advection. The simulation results show that the solute transported in a failed shaft can reach the shallow bedrock groundwater zone. These results might imply that a failed shaft will substantially lose its effectiveness as a barrier. The fourth application is proposed to investigate the geochemical evolution of sedimentary host rock in a near field scale. In this part, a new thermo-hydro-mechanical-geochemical simulator (COMSOL-PHREEQC) is developed. It is anticipated that there will be a geochemical reaction within the host rock that results from interaction with the water enriched with the CO2 generated by nuclear waste.

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Excavations at Natural Trap Cave (NTC) began in the mid-1970's and quickly yielded evidence of a diverse steppe fauna that existed during the Last Glacial Maximum (MIS 2) along the western slope of the Bighorn Mountains in north central Wyoming. NTC is a karst pit cave with a 24.5 m vertical drop into a roughly 43 m wide bell-shaped ‘Main Chamber’ and during the course of early excavations a plugged entrance to a fossil-bearing ‘Lower Chamber’ was discovered. Stratigraphic relationships below the entrance to the Main Chamber of the cave were originally studied in the mid-1970's, but were never formally published. Although stratigraphy, taphonomy, and depositional circumstances were briefly discussed over the following years, little has been done to correlate the numerous stratigraphic schemes used by various authors. In this study, four stratigraphic sections were measured and analyzed to establish an easily modifiable lithostratigraphic system of nomenclature. We provide the first correlations of all stratigraphic nomenclature used throughout excavations at NTC to facilitate comparisons with current and previous collections and publications. By leveraging more than 100 radioisotopic dates we developed an age-depth model and chronostratigraphic framework to further interrogate spatiotemporal relationships between strata, paleoenvironmental proxies, and fossil assemblages. Deposition is shown to be discontinuous; sediment accumulation in the study area is restricted to the buildup through peak penultimate and Last Glacial maxima. More recent (<10 ka) Holocene deposits unconformably cover the eroded surface of underlying Pleistocene strata. There is active reworking of sediments with transport and deposition of reactivated material within the Lower Chamber. We note that the two hiatuses coincide with interglacial periods and may reflect changing depositional circumstances within the cave such as extended periods of non-deposition, erosion, or bypass (possibly leading to deposition in the Lower Chamber). Contrary to previous reports, we demonstrate that it is unlikely a prominent snow cone existed or contributed to the pattern of sediment and fossil distribution within the study area, furthermore, we do not observe a continuous Pleistocene-Holocene transition in the study area. Further stratigraphic work will be needed to better understand the interrelationship between Main and Lower chamber deposits and the evolution of sediment accumulation in NTC.

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Située dans la partie occidentale de la République Centrafricaine, la zone d’étude (Fig.1 et 18), correspond à trois domaines géotectoniques : le domaine NW et SE, le domaine central et le domaine méridional. Le domaine NW et SE ou la nappe panafricaine des Gbayas (640 Ma), est caractérisé par une succession d’activités magmatiques et de granulites. Le mouvement tectonique affectant ce domaine est principalement latéral ( vers le S et SW). Le domaine central, constitué d’un socle éburnéen (2400-2200 Ma) et de sa couverture paléoprotérozoïque métasédimentaire à métavolcanite (1800 Ma environs), est dominé par des mouvements verticaux.Le dernier domaine comporte, une triade de roches (métatillite, cipolin, métasilexite) néoprotérozoïques, associées au dépôts du bassin de Bangui, est coiffée par une formation sédimentaire. S’agirait-il de deux domaines paléogéographiques (central et méridional) juxtaposés ? La lithologie et la lithostratigraphie de ces deux précédentes zones posent toujours des problèmes d’âges.). Les métatillites situés à la partie basale des dépôts du bassin de Bangui (domaine méridional), nous ont poussé à vérifier les traces de l’événement mondial qui est la glaciation néoprotérozoïque, en réalisant des analyses géochimiques au ∂18O et ∂13C. Ces trois domaines portent les empreintes de quatre à trois phases de déformation panafricaine. Des fortes valeurs d’aimentation (≤ 5 A/m ) mesurées sur certaines roches issues de cette zone pourraient être associées à la grande anomalie magnétique observée mondialement (satellitaire et au sol ) en République Centrafrique. / Located in the western part of the Central African Republic, the study area (Fig. 1 and 18), corresponding to three geotectonic areas: NW and SE area, central area and the southern area. The NW and SE domain or Pan Gbayas of water (640 Ma) is characterized by a succession of magmatic activity and granulites. The tectonic movement affecting this area is mainly lateral (to the S and SW). The central domain consists of a Eburnean basement (2400-2200 Ma) and its Paleoproterozoic metasedimentary to metavolcanic coverage (around 1800 Ma) is dominated by vertical movements.The latter area includes a triad of rocks (métatillite, cipolin, métasilexite) Neoproterozoic, associated with basin deposits Bangui, is capped by a Stack. Would it two paleogeographic domains (central and southern) side by side? Lithology and lithostratigraphy of the two previous areas still pose problems for ages.). The métatillites located at the basal part of Bangui Basin (southern area) deposits, we drove to check the traces of the global event that is Neoproterozoic glaciation, conducting geochemical analyzes ∂ 18O and ∂ 13C. These three areas are the fingerprints of four three-phase deformation of Pan. Strong values of magnetization (≤ 5 A / m) measured on some rocks from this area may be associated with high magnetic anomaly observed worldwide (satellite and ground) in the Central African Republic.

Cette thèse est consacrée à l’étude de l’interaction cryosphère-climat depuis le milieu du Pliocène jusqu’au quaternaire pendant l’installation pérenne de la calotte groenlandaise. Nous étudions d’abord les causes du développement et de la disparition de l’importante mais courte glaciation qui a eu lieu pendant le stade isotopique marin M2 (MIS M23.264-¬3.312 Ma). Ensuite, dans le cadre du programme international sur la modélisation du Pliocène (PLIOMIP2), nous étudions le climat de la période chaude du Plaisancien moyen(MPWP, 3.3-3.0Ma). Enfin, la troisième période étudiée est la transition Plio-Pléistocène transition (PPT, 3.0-2.5Ma), que nous avons étudiée grâce à un couplage asynchrone entre un modèle de climat et un modèle de calotte. A travers ces différentes périodes, nous avons amélioré la connaissance des relations entrepCO2, tectonique et climat pendant la transition d’un monde chaud et riche en CO2 vers le monde bien plus froid et à faible pCO2 des glaciations quaternaires. Ce résultat montre l’importance de mieux comprendre les relations entre dynamique océanique, pCO2 et climat. / This thesis is devoted tounderstanding the interaction betweencryosphere and climate from the mid Plioceneto the early Quaternary during the onset ofNorthern Hemisphere Glaciation (NHG).Firstly, we investigate the causes for thedevelopment and decay of the large but shortliving glaciation that occurred during MarineIsotope Stage 2 (M2, 3.264-¬3.312 Ma);Secondly, in the framework of the internationalPliocene Model Intercomparison Project(PLIOMIP2), we study the climate of Mid-Piacenzian Warm Period (MPWP, 3.3-3.0Ma).Thirdly, we explore the Plio-PleistoceneTransition (PPT, 3.0-2.5Ma) with anappropriate asynchronously coupled climatecryosphere model. Through these differentperiods, we provide a better understanding ofthe relationship between pCO2, tectonics andclimat during the transition from a warm andhigh-CO2 world to the cold and low-CO2Quaternary glaciations. This work also pointsout the necessity to further study the linkbetween ocean dynamics, carbon cycle andclimate.