In a warming world, glaciers and ice sheets have an increasingly large influence on the environment, particularly through their contribution to sea level rise. Their response to anthropogenic climate change, in addition to natural variability, has a critical impact on dependent populations and will be key to predict future climates. Understanding the past natural transitions is also important as if the natural variability of the climate system is not well understood, we stand little change of accurately predicting future climate changes, especially in the context of rapid global warming. Ice cores represent the best time capsules for the recovery of paleo-climate informations. For that, the recovery of a suitable 1.5 million-year-old ice core in Antarctica is fundamental to better understand the natural climate reorganisation which occurred between 0.9 and 1.2 Ma. Constraining the englacial and basal temperature evolution of glaciers and ice sheets through time is the first step in understanding their temporal stability and therefore potential impacts on climate. Furthermore, obtaining the best constraints on basal conditions is essential as such million-year-old ice will be located very near to the bedrock, where the thermal regime has the strongest impact. However, measurements of current englacial and basal temperature have only been obtained at a few drill sites for glaciers and ice sheets. We must therefore turn to thermodynamical models to provide theoretical and statistical constraints on governing thermal processes. Thermodynamical models rely on a suite of governing equations, which we describe in this thesis. Our first study area is the McCall glacier, in Alaska (USA), where we show that the glacier cooled down in the warming climate of the last 50 years using a 1D thermodynamical model. We calculate the present-day englacial temperature distribution using recently acquired data in the form of englacial temperature measurements and radio-echo sounding surveys of the glacier. We show the important of absence of latent heat release due to the refreezing of meltwater inside an active surface layer and reconstruct the last 50 years of equilibrium line altitude (ELA) elevation changes. In the context of Beyond Epica Oldest Ice, a European project aimed at recovering a 1.5 million year-old ice core, we propose for the first time a map of the location of adequate drilling sites for the entire Antarctic Ice Sheet. We use a 3D thermomechanical model to calculate a new basal temperature map of the Antarctic Ice Sheet, as well as a 1D thermodynamical model to constrain the poorly known geothermal heat flux (GHF). These combined model runs use the latest acquired data sets for the GHF, ice flow velocity, ice thickness and subglacial lakes. In order to take into account 2 Ma of Antarctic climate history, we use a transient 1D thermodynamical model to provide constraints on GHF by calculating the maximum value of GHF allowed to keep frozen basal conditions everywhere underneath the ice sheet. These values are then statistically compared to published GHF data sets to propose a probabilistic map of frozen and thawed bedrock locations. This transient model uses high spatial resolution radar data acquired over the Dome Fuji and Dome C regions to examine their likelihood of having preserved 1.5-million-year ice. We define a number of important criteria such as GHF, bedrock variability, ice thickness and other parameter values for Oldest Ice survival. We anticipate that our methods will be highly relevant for Oldest Ice prospection in other areas of the ice sheet that so far remain little or un-surveyed, as well as for the thermal modelling of other glaciers and ice sheets, and in particular, of the Greenland Ice Sheet. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Le climat primitif martien fascine la recherche martienne. Identifier avec le plus de précision possible les conditions primitives martiennes permettrait de contraindre les différents états de l’eau au cours de l’histoire martienne. Aujourd’hui deux hypothèses font débat, la première est celle d’un climat chaud et humide régnant à la surface de Mars à la fin du Noachien/début Héspérien. La deuxième, à l’inverse, semble indiquer que le climat aurait été froid et englacé sur les plus hautes altitudes martiennes. Néanmoins, cette deuxième hypothèse est souvent contestée, car contrairement à la présence de marqueur d’eau liquide à la surface de Mars, aucune morphologie de surface attestant d’un climat froid n’avait été identifiée. Au cours de cette thèse, nous avons étudié de manière morphométrique les structures et morphologies à la surface de Terra Sabaea, qui constitue 1% de la superficie totale de la planète. Ces structures constituent des héritages morphologiques des activités climatiques passées. Afin de caractériser au mieux l’origine érosive de ces structures, nous avons créé une nouvelle méthode d’analyse morphométrique à partir de différentes méthodes terrestres et martiennes. Cette nouvelle méthode permet d’extraire plus de 20 données exploitables par vallée. Il a donc été question de mesurer un maximum de vallée afin d’établir une base de données que nous avons comparée avec des bases de données de morphologies terrestres et martiennes. Grâce à cette analyse, il a été possible de mettre en évidence, la présence d’un paysage glaciaire dans la région de Terra Sabaea. Ce paysage est composé de (1) vallées glaciaires liées avec (2) des cirques glaciaires. La source de cette glace semble être (3) des calottes de plateaux locales à des altitudes > 3500 m. Nous avons donc démontré pour la première fois la présence de morphologies glaciaires attestant d’un climat froid il y a 3.6 Ga. Néanmoins, la présence de telles morphologies n’indique pas que l’ensemble de Terra Sabaea était englacé. L’analyse morphométrique a démontré la présence de morphologie fluviatile géographiquement proche des morphologies glaciaires et souvent à la même altitude, entre 1500 et 3500 m. Cette observation nous a permis de mettre en évidence (4) que la pente était un facteur qui influençait sur l’état de l’eau. En effet, pour une même altitude, les morphologies fluviatiles sont situées sur les pentes douces (< 3°) alors que les morphologies glaciaires sont situées sur les remparts internes des cratères d’impacts présentant une forte pente (> 10°). Cependant (5) l’altitude semble également être un facteur déterminant puisque l’on ne retrouve pas de morphologie glaciaire à des altitudes < 1500 m. L’analyse des terrains de Terra Sabaea a également mis en évidence (6) qu’il existait un lien génétique entre les morphologies glaciaires de hautes altitudes et les vallées fluviatiles plus bas. En effet, il est possible de suivre une vallée qui prend sa source sur les hauts plateaux englacés en amont, jusqu’en aval où elle rejoint des morphologies témoignant d’une activité fluviatile. Cette continuité dans les morphologies glaciaires et fluviatiles permet (7) de mieux définir l’origine des vallées ramifiées, et notamment l’origine de Naktong vallis, et il semblerait que la fonte des glaces a joué un rôle dans leurs formations. De plus, cette continuité morphologique permet de supposer qu’il existait (8) un cycle de l’eau similaire à la Terre dans la région de Terra Sabaea il y a 3.6 Ga. / The primitive Martian climate fascinates Martian research. Identifying Martian primitive conditions as accurately as possible would make it possible to constrain the different states of water during Martian history. Today two hypotheses are debated, the first is that of a hot and humid climate prevailing on the surface of Mars at the end of the Noachian / early Hesperian. The second, on the contrary, seems to indicate that the climate was cold and glacial on the highest Martian altitudes. Nevertheless, this second hypothesis is often disputed, because unlike the presence of liquid water marker on the surface of Mars, no surface morphology attesting to a cold climate had been identified. In this thesis, we studied morphometrically structures and morphologies on the surface of Terra Sabaea, which constitutes 1% of the total surface of the planet. These structures constitute morphological legacies of past climatic activities. In order to better characterize the erosive origin of these structures, we have created a new method of morphometric analysis from different terrestrial and Martian methods. This new method makes it possible to extract more than 20 exploitable data per valley. It was therefore a question of measuring a valley maximum in order to establish a database that we compared with databases of terrestrial and Martian morphologies. Thanks to this analysis, it has been possible to highlight the presence of an ice landscape in the Terra Sabaea region. This landscape is composed of (1) glacial valleys linked or not with (2) glacial cirques. The source of this ice appears to be (3) local plateau caps at altitudes> 3500 m. We thus demonstrated for the first time the presence of glacial morphologies attesting to a cold climate there are 3.6 Ga. Nevertheless, the presence of such morphologies does not indicate that the whole of Terra Sabaea was glaciated. Morphometric analysis has demonstrated the presence of fluvial morphology geographically close to glacial morphologies and often at the same altitude, between 1500 and 3500 m. This observation allowed us to highlight (4) that the slope was a factor influencing the state of the water. Indeed, for the same altitude, fluvial morphologies are located on gentle slopes (<3 °) while glacial morphologies are located on the inner walls of impact craters with a steep slope (> 10 °). However (5) altitude also seems to be a determining factor since we do not find glacial morphology at altitudes <1500 m. Terra Sabaea land analysis also revealed (6) that there is a genetic link between high altitude glacial morphologies and lower river valleys. Indeed, it is possible to follow a valley that has its source on the highlands glaciers upstream, downstream where it joins morphologies testifying to a fluviatile activity. This continuity in glacial and fluvial morphologies makes it possible (7) to better define the origin of branched valleys, and in particular the origin of Naktong vallis, and it seems that melting ice has played a role in their formations. Moreover, this morphological continuity makes it possible to suppose that there existed (8) a cycle of water similar to the Earth in the region of Terra Sabaea there is 3.6 Ga.

No description available.

Elevation, longitudinal profile, and Schmidt hammer data indicate that strath terraces (specifically the lower elevation terraces) mapped in the Fremont River drainage of Capitol Reef National Park are correlative to the terraces of the smaller Pleasant Creek drainage located approximately ten miles to the south. This correlation suggests that drainage development in this area of the Colorado Plateau was strongly dependent upon a regional-scale forcing mechanism (e.g. climate) rather than strictly independent basin-scale processes. Elevations of mapped strath terraces and their associated black volcanic boulder deposits were calculated from geologic maps, Digital Elevation Models (DEM), and Digital Orthophoto Quadrangles of the Fruita and Golden Throne Quadrangles, Wayne and Garfield Counties, Utah. Terraces in both drainages were placed into twenty foot elevation bins and then gathered into larger terrace levels based upon population breaks and the degree of weathering as seen from Schmidt hammer hardness data. Comparison of the two datasets indicate that the two lowest terrace levels of the Fremont River compare well with the two terrace levels of Pleasant Creek both in elevation above the present stream bed and in Schmidt hammer hardness measurements. Our data demonstrate that the Fremont River drainage is likely much older than the smaller Pleasant Creek drainage. Further, correlative terrace data strongly suggests that glacial-interglacial climate forcing played a dominant role in the landscape evolution of both drainages and by inference, the broader Colorado Plateau. Terrace elevation data were compared with recently published cosmogenic ages for several terrace deposits located within the Fremont River drainage. This comparison provides compelling evidence that highest concentrations of preserved terraces may be time correlative with discrete isotopic stages associated with glacial maximum and/or deglacial conditions. Finally, our data also demonstrate that in this area of the Colorado Plateau incision rates are on the order of ~60 to 85 cm/ka, which is on the high end of reported rates from other researchers.

The late Mississippian carbonates in the Appalachian Basin, U.S.A., were deposited on a huge, south-facing ramp during long-term Mississippian transgression that formed the Mississippian supersequence. The St. Louis- to Glen Dean interval consists of up to twelve fourth-order depositional sequences (300 to 400 k.y. average duration). The sequences (a few meters to over a hundred meters thick) consist of eolianites, lagoonal carbonate muds, ooid shoals, and skeletal banks, and open marine skeletal wackestone and basinal marion the ramp-slope and basin margin. Sequence boundaries are at the top of prograding red-beds, eolianites, and shoal water facies on the ramp, and beneath lowstand sand bodies and quartzose calcisiltite wedges on the ramp margin and slope. Maximum flooding surfaces are difficult to map regionally, therefore it is difficult to separate the TST from the HST of these fourth-order sequences. / Ph. D.

The major purpose of this study is to evaluate the paleoenvironmental and paleoclimatological conditions during the Middle Miocene-Early Pliocene in Kalecik-Ankara by using mineralogical and geochemical proxies from Han&ccedil / ili Formation. To achieve a high-resolution paleoclimate data, 2 stratigraphic sectioning and 1 continous core drilling were examined. Field studies were followed by analytical techniques on the selected representative samples. The mineralogical compositions of the bulk samples and the minerals of the clay fractions were determined by X-ray diffractometer. Scanning electron microscopic analyses were also carried on the specific samples which have the potential to define the important microstructural units. The major and trace elemental compositions were determined by X-ray fluoresence spectrometer. Additionally, the stable isotope compositions of the samples selected from the continous core drilling on Han&ccedil / ili formation were among the major proxies to gather a paleoenvironmental and paleoclimatrological approach. All the proxies employed for this study clearly indicate that mineralogical and geochemical signatures are consistent with each other and can be used for paleoclimatic interpretations. The stable isotope values point that C4 plants were dominant during the deposition of Han&ccedil / ili Formation, while evaporation caused the development of alkaline environment which is seasonally dry with depositional temperature approximately between 25-30&deg / C. During deposition, lava flowand tuff were deposited due to the volcanic activity in the vicinity of the lake. Based on this volcanism, economical bentonite deposits were originated. The lake at which the Han&ccedil / ili formation was deposited, completed its development in a time to time silicate rich and salty-alkaline anvironment.

Ce manuscrit concerne l'analyse tectonique et géomorphologique du système de failles de Longriba (LFS), localisé à l'Est du plateau tibétain à environ 200 km au Nord-ouest de la chaîne des Longmen Shan. Le LFS est constitué de deux zones de failles décrochantes dextres, parallèles et d'orientation N55°E : la faille de Longriqu, au Nord, et la faille de Maoergai, au Sud. Le rôle géodynamique de ce système est primordial puisqu'il accommode 5 ± 1 mm/an de la composante décrochante induite par la convergence oblique du bloc Aba, elle-même liée à la collision Inde-Asie. De plus, le LFS partitionne la déformation de la marge Est tibétaine; les structures des Longmen Shan étant essentiellement chevauchantes. Cependant l'histoire long-terme du LFS est mal contrainte. L'objectif de cette thèse est donc d'apporter des informations spatio-temporelles sur l'activité du système à l'échelle du Cénozoïque. Pour cela trois études ont été réalisées. La première a permis de mieux contraindre le comportement sismogénique des deux zones de failles à l'aide d'images satellites de basse (90m) et très haute résolution (50cm). L'analyse des déplacements cumulés le long de la faille de Maoergai a permis de proposer que celle-ci était active vers ~15Ma. La seconde étude a mis en évidence un contrôle du système sur la répartition des taux de dénudation au travers de la marge Est tibétaine à l'échelle de l'Holocène. Enfin, les données de thermochronologie basse température suggèrent que la faille de Maoergai a accommodé un mouvement vertical vers ~10Ma. Ce mouvement est probablement lié au rebond isostatique de la marge, découplé du mouvement décrochant qu'elle accommode à la même période. / This manuscript concerns the tectonic and geomorphic analysis of the Longriba fault system (LFS), located in the eastern Tibetan plateau at about 200 km north-west of the Longmen Shan. The LFS consists of two dextral strike-slip fault zones, parallel and N55 °-trending: the Longriqu fault to the north and the Maoergai fault the south. The geodynamic role of the system is essential as accommodates 5 ± 1 mm / year of the slip component induced by the oblique convergence of the Aba block, itself linked to the India-Asia collision. In addition, the LFS partitions the deformation of the east Tibetan margin; the structures of the Longmen Shan are mainly thrust faults. However the long-term history of LFS is poorly constrained. The objective of this thesis is to bring spatial and temporal information on system activity throughout the Cenozoic. To do so, three studies were performed. The first led to better constrain the seismogenic behavior of the two fault zones with low resolution (90m) and very high resolution satellite images (50cm). The analysis of cumulative displacements along the Maoergai fault allowed to propose that it was active at ~ 15 Ma. The second study showed that the system controls the distribution of the denudation rates over the EastTibetan margin throughout the Holocene. Finally, the low-temperature thermochronology data suggest that, in particular, the Maoergai fault has accommodated a vertical movement at ~ 10 Ma. This movement is probably related to the isostatic rebound of the margin, decoupled from the strike-slip movement it accommodates at the same period.