Les objectifs de cette thèse sont d’étudier la sédimentation dans des sous bassins privilégiés du Golfe du Mexique (Bassin de Pigmy et de La Salle) afin de reconstituer la variabilité des apports détritiques via le fleuve Mississippi au cours du dernier cycle climatique. Une approche intégrée couplant minéralogie, granulométrie, géochimie élémentaire et organique, dans un cadre chronostratigraphique précis, a permis de progresser dans la compréhension des relations entre les mécanismes climatiques de moyenne et haute latitude et l’hydrologie du domaine subtropical et de proposer des schémas d’interprétation du couplage océan-atmosphère. La minéralogie contrastée des zones en érosion drainées par le système fluviatile du bassin versant du Mississippi permet de contraindre les zones continentales qui vont successivement alimenter la sédimentation du Golfe du Mexique. Les modifications des sources détritiques ainsi mises en évidence au cours du dernier cycle climatique ont permis (1) de contraindre la localisation des zones de déstabilisation de la marge Laurentide et l’enchaînement des processus sédimentaires lors des décharges d’eau douce qui caractérisent la dernière déglaciation, (2) de mettre en évidence une modification du front de précipitations associée aux périodes de mégacrue du Mississippi lors des périodes interglaciaires et d’en déduire des informations sur le régime hydrologique et (3) de suggérer des schémas de transferts méridiens d’humidité contrastés lors des stades interglaciaires 1 et 5e, suggérant des configurations atmosphériques sensiblement différentes. La confrontation de ces résultats avec d’autres données paléoclimatiques a alors permis de proposer plusieurs modèles simples pour les interactions océan-atmosphère dans le Golfe du Mexique, basés sur les modifications des configurations atmosphériques (Jet Stream et ITCZ) et océaniques (extension de l’Atlantic Warm Pool) et confirme le rôle majeur de l’atmosphère comme vecteur de la variabilité climatique rapide. / The objectives of this thesis are to study the sedimentary features of some basins of the Gulf of Mexico (Pigmy and La Salle basins) in order to reconstitute the variability of the detrital input via the Mississippi River during the last climatic cycle. An integrated approach coupling mineralogy, granulometry, and geochemistry (inorganic and organic), within a precise chronostratigraphic framework, allows to progress in the understanding of the relations between the mid- and high-latitude climatic mechanisms and the subtropical hydrology, as well as to propose synoptic models of the ocean-atmosphere coupling. The contrasting mineralogy of the zones drained by the catchment system of the Mississippi River watershed allows constraining the continental zones which will successively feed the sedimentation of the Gulf of Mexico. The modifications of the detrital sources revealed for the last climatic cycle enabled (1) to track down the localization of the zones of destabilization of the southern margin of the Laurentide Ice Sheet and the sequence of sedimentary processes during the freshwater discharges, which characterized the last deglaciation, (2) to highlight modifications of the precipitation front which were associated with episodes of large Mississippi River floods during interglacial times, and therefore, to deduce information on the hydrological regime, and (3) to suggest schematic models of meridian transfer of moisture contrasted during interglacial stages 1 and 5e, suggesting an appreciable difference in the atmospheric configurations. The confrontation of these results with other paleoclimatic records allowed to propose simple models of the atmosphere-ocean-continent interactions recorded in the Gulf of Mexico, which are based on the modifications of both the atmospheric configurations (Jet Stream and ITCZ) and oceanic (extension of Atlantic Warm Pool). These models confirm the major role of the atmosphere as a vector of rapid climatic variability

Les eaux du Golfe du Mexique (GOM) jouent un rôle important dans le systéme climatique global car elles Intluencent les propriétés hydrologiques du Gulf Stream (GS), courant océanique chaud de surface faisant partie Intégrante de la circulation thermohaline (THC). Au cours du dernier cycle climatique, d'énormes écoulements d'eau douce, provenant de la fonte de la calotte Laurentide sur le continent-nord américain, se sont déversées au sein du GOM. moditiant ses caractéristiques hvdrologlques et donc celles du GS. Ces perturbations auraient pu, en altérant la THC, affecter le systéme climatique. La compréhension des transferts entre le continent nord-américain et le GOM au cours du dernier cycle climatique s'avére donc primordiale. En connaissant les principales sources continentales, les facteurs influençant le transport (réalisation de cartes de répartition des minéraux argileux sur le continent nord-américain et dans les sédiments du GOM) et la sédimentation (par modélisation analogique) du matériel terrigéne fin, l'étude des enregistrements sédimentaires (minéralogie des argiles, granulométrie ) et isotopiques ([delta]18O) de deux bassins du nord du GOM (Bassins d'Orca et d'Humphrey) a permis d'appréhender les transferts entre le continent nord-américain et le GOM au cours du dcrnier cycle climatique. La variabilité des apports détritiques du Mississippi et des fleuves du sud-ouest des États-Unis a pu être reliée aux variations paléo-environnementales (fonte de la calotte Laurentide et des glaciers des Montagnes Rocheuses) et paléoclimatiques (modifications des transferts d'humidité depuis le GOM vers le continent) qui affectent le continent nord-américain / The Gulf of Mexico (GOM) is a key area for the global thermohaline circulation (THC) and for the global-climatic system, since its hydrological characteristics (hlgh salinity and temperature) partly control Gulf Stream physical properties. Dunng the last climatic cycle, GOM hydrology was impacted by episodic freshwater inputs via the Mississippi River resulting from intermittent meltmg of the Laurentide Ice Sheet (LIS). The resulting salinity changes affected the THiC. global heat exchange and worldwide climatie conditions. Direct effeets of these freshwater supplies on the GOM paleoceanography have been documented studying the planktonic foraminifera [delta]18O evolution By contras!. terrigenous inputs associated with these meltwater pulses are poorly understood. These detrital fractions are. however. IIkeiv to provide information on the link between continental and marine records during the last climatic cycle. An overview of the main continental detrtital source areas, of the dominant factors controlling clav minerai transport patterns (by drawing clay minerai distribution maps in the US and northem GOM) and of thin terrigenous particle sedimentation in the GOM (by analogical modeIing), lays the groundwork for the use of clay-minerai assembiages for understanding the connection between North America and the GOM. The downcore investigations of sedimentary (clay mineralogy, grain-slze . .) and isotopic ([delta]18O) records ln two minibasins of the GOM (Orca Basin and Basin 4) allow us to explain the fluvial inputs variations, during the last climatic cycle, by paleoenvironmental (ice meltback) and paleocllmatic (atmospheric circulation) fluctuations that affected North America

No description available.

Ice stream research has gained momentum in the last decade due to the increased need to understand ice sheet dynamics and instability and, by extension, the role ice streams have on climate change and sea level rise. Although significant progress has been made recently in understanding the role of ice streams in ice sheet dynamics, much remains to be done for documenting and understanding paleo-ice stream records. This is especially true for terrestrial paleo-ice streams like those that operated in the southwest Laurentide Ice Sheet. In previous studies evidence was shown for at least two large paleo-ice stream systems in southern Saskatchewan and a model was proposed involving major glacial dynamics shifts during the Late Wisconsinan linked to ice streaming in the Prairies. The goal of this research is to further characterize drift provenance and to verify sediment-landform assemblages that are central to the proposed reconstruction. This is done through spatial analysis of sediment and landform characteristics (e.g. compositional data, till fabric, landform identification). Provenance is also investigated using radiometric data and 40Ar/39Ar dating of hornblende grains. All of the data are geo-referenced in GIS to examine the spatial relationships. Results show spatially consistent patterns that fit within the structure of the proposed ice stream model. Ten assemblages were delineated, some showing landform evidence of southwestern and southeastern flow, while others show an older western signature through compositional data. The ice flow dynamics were characterized by a combination of landform evidence and compositional data, where three distinct ice flow phases can be seen. Of these three flow phases, two can be characterized by paleo-ice streams. The older south westward Maskwa system flowed against the regional slope, creating a large area of mega-scale glacial lineations, as well as transverse ridges, and was bound on either side by hummocky terrain. The preservation of the southwest Maskwa system was due to the abrupt shift to the southeastward Buffalo system. The Buffalo system captured the subglacial water from the Maskwa causing its shutdown, which fed the James Lobe until it collapsed. The Buffalo paleo-ice stream was the youngest and least stable of the two systems, as shown in the cross-cutting landform evidence. This approach combines multiple methods of analysis to go beyond the geomorphologic evidence to test the main underlying assumptions of paleo-ice stream landsystem models. This is critical if we are to understand the processes involved in the formation of paleo-ice streams and to reconstruct their evolution. Further characterization of the paleo-ice stream systems in the Prairies is critical to improve our understanding of how large ice sheets, like the Laurentide Ice Sheet, evolved and eventually collapsed.

Ice stream research has gained momentum in the last decade due to the increased need to understand ice sheet dynamics and instability and, by extension, the role ice streams have on climate change and sea level rise. Although significant progress has been made recently in understanding the role of ice streams in ice sheet dynamics, much remains to be done for documenting and understanding paleo-ice stream records. This is especially true for terrestrial paleo-ice streams like those that operated in the southwest Laurentide Ice Sheet. In previous studies evidence was shown for at least two large paleo-ice stream systems in southern Saskatchewan and a model was proposed involving major glacial dynamics shifts during the Late Wisconsinan linked to ice streaming in the Prairies. The goal of this research is to further characterize drift provenance and to verify sediment-landform assemblages that are central to the proposed reconstruction. This is done through spatial analysis of sediment and landform characteristics (e.g. compositional data, till fabric, landform identification). Provenance is also investigated using radiometric data and 40Ar/39Ar dating of hornblende grains. All of the data are geo-referenced in GIS to examine the spatial relationships. Results show spatially consistent patterns that fit within the structure of the proposed ice stream model. Ten assemblages were delineated, some showing landform evidence of southwestern and southeastern flow, while others show an older western signature through compositional data. The ice flow dynamics were characterized by a combination of landform evidence and compositional data, where three distinct ice flow phases can be seen. Of these three flow phases, two can be characterized by paleo-ice streams. The older south westward Maskwa system flowed against the regional slope, creating a large area of mega-scale glacial lineations, as well as transverse ridges, and was bound on either side by hummocky terrain. The preservation of the southwest Maskwa system was due to the abrupt shift to the southeastward Buffalo system. The Buffalo system captured the subglacial water from the Maskwa causing its shutdown, which fed the James Lobe until it collapsed. The Buffalo paleo-ice stream was the youngest and least stable of the two systems, as shown in the cross-cutting landform evidence. This approach combines multiple methods of analysis to go beyond the geomorphologic evidence to test the main underlying assumptions of paleo-ice stream landsystem models. This is critical if we are to understand the processes involved in the formation of paleo-ice streams and to reconstruct their evolution. Further characterization of the paleo-ice stream systems in the Prairies is critical to improve our understanding of how large ice sheets, like the Laurentide Ice Sheet, evolved and eventually collapsed.

Indiana University-Purdue University Indianapolis (IUPUI) / A broad range of samples were collected from the Huron-Erie Lobe, Lake Michigan Lobe, Saginaw Lobe, and Tipton Till Plain of northern Indiana to determine the provenance of Laurentide Ice Sheet till in the Midwest U.S. during the Illinoian and Wisconsinan glaciations. U-Pb age distributions from approximately 300 detrital zircons (DZ) were used as provenance indicators for each till sample. Till from the Lake Michigan Lobe and was found to be largely homogenized. The distinct lobe DZ age distributions are the Lake Michigan Lobe till with a dominant ~1465 Ma peak, the northern Huron-Erie Lobe till with a dominant ~1060 Ma and a secondary peak at ~1450 Ma, the southern Huron-Erie Lobe till with nearly equal peaks at ~1435 Ma, ~1175 Ma, and ~1065 Ma, and the southern Saginaw Lobe till with a dominant peak at ~1095 Ma. Those four DZ age distributions were treated as endmembers in a nonlinear least-squares mixing model to calculate the contribution of each lobe to till in the Tipton Till Plain. Huron-Erie and Saginaw lobe tills were found to be the primary components of the Tipton Till Plain, and Lake Michigan Lobe till was only found in the western Tipton Till Plain. Zircons from the Saginaw Lobe till increased 39 % in the eastern Tipton Till Plain between the Illinoisan and Wisconsinan glaciations. The mixing model was also applied to relate the DZ age distributions of the lobes to bedrock within and near their flow paths. When comparing nearby bedrock to each lobe’s till, mixing model results, yield an approximate maximum transport distance between 500 and 630 kilometers for the matrix vii fraction of till in the Lake Michigan, Huron-Erie, and Saginaw lobes. Samples for the southern Huron-Erie Lobe indicate that the most of the zircon ages within the southern Huron-Erie Lobe till in Indiana were specifically entrained between Niagara County, New York and east-central Indiana. Within the model’s error, 93 – 100 % of the detrital zircons in each of the three lobes are relatable to nearby Paleozoic and Precambrian sedimentary and metamorphic bedrock formations.

Cette thèse concerne la modélisation des calottes de glace qui ont couvert l'hémisphère nord durant les dernières périodes glaciaires. Des améliorations de la physique ont été effectéees sur le modèle de calotte de glace Antarctique du LGGE, nommé GRISLI, afin de rendre ce modèle portable sur l'hémisphère nord. Une nouvelle méthode pour déterminer la position du front des ice shelves (plates-formes de glace flottante) a été mise au point, des conditions aux limites spécifiques au front des ice shelves ont été ajoutées. Un nouveau schéma pour le drainage de l'eau sous-glaciaire et un critère basé sur la pression de l'eau sous-glaciaire ont permis de localiser les ice streams (ou fleuves de glace) de façon bien plus réaliste qu'auparavant. Ce nouveau modèle est appliqué aux calottes de l'hémisphère nord et simule leur évolution lors du dernier cycle glaciaire-interglaciaire en comparant l'impact relatif du bilan de masse en surface et de la dynamique. L'évolution de la calotte eurasienne aurout de l'évènement à 90 000 ans (BP) a été détaillée pour étudier l'impact des lacs proglaciaires et le rôle des ice shelves pendant l'avancée et le retrait sur les mers de Barents et de Kara.

Thesis advisor: Jeremy D. Shakun / The deglacial extent chronology of the southeastern Laurentide Ice Sheet as it retreated through the northeastern United States and southern Quebec has been well constrained by multiple lines of evidence. By comparison, few data exist to constrain the thinning history of the southeastern Laurentide, resulting in lingering uncertainty about volume changes and dynamics of this ice mass during the deglacial period. To address the lack of thinning information, my team collected 120 samples for in-situ `10Be exposure dating from various elevations at numerous mountains in New England and southern Quebec. Monte Carlo regression analyses using the analytical uncertainties of exposure ages from each mountain are used to determine the most-likely timing and rate of ice thinning for that location, a technique known as the ‘dipstick approach’. While this larger project is ongoing, I have processed and measured 10Be concentrations of 42 samples for this thesis and present my preliminary results and interpretation here. Exposure ages from Peekamoose Mt. in southern NY suggest ice thinning early in the deglacial period (~19.5 – 17.5 ka), near the onset of the Heinrich Stadial I cold period. Samples from Franconia Notch, NH, and Mt. Mansfield, VT, suggest ice thinning from approximately 15 – 13 ka in northern New England, roughly coincident with the Bølling-Allerød warm period. Exposure ages from each of the northern New England dipsticks are nearly identical within 1σ internal uncertainty, indicating that ice thinning was rapid. Higher elevation (>1200 m a.s.l.) samples from the northern New England mountains appear to contain inherited 10Be from previous periods of exposure, indicating a lack of glacial erosion on these surfaces. My high-elevation samples with inherited 10Be suggest that these summit landscapes were preserved beneath cold-based, non-erosive ice during the last glacial and deglacial periods. 40 samples that have yet to be processed will provide more information on ice thinning around Killington Mt., VT, Mt. Greylock, MA, Mt. Bigelow, ME, and Mt. Jacques-Cartier, Quebec. Ultimately, this information will be used to create probabilistic reconstructions of the lowering southeastern Laurentide ice surface during its retreat. / Thesis (MS) — Boston College, 2018. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

No description available.

No description available.