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.

Long term fluvial incision spanning the Late Cenozoic is recorded in many fluvial systems around the world by terrace landform sequences. The incision manifests itself as inset sequences of river terraces which form terrace staircases. The timing of the onset of incision and the rate incision then proceeds at is poorly constrained due to the difficulties in dating river terraces. This study applies the technique of cosmogenic exposure dating to a fluvial staircase, for the first time, in the Sorbas Basin, SE Spain. Cosmogenic exposure dating allows the timing of abandonment of the fluvial terraces to be calculated therefore recording periods of incision. Cosmogenic exposure dating and the profile method offer a viable way to date Early and Middle Pleistocene terrace deposits. Combined exposure and burial age’s approaches using paired isotopes allow for insights into terrace aggradation and fluvial incision timing. The fluvial deposits in the Sorbas Basin record 1.0 Ma of incision by the Río Aguas. The timing of aggradation and incision in the Sorbas basin has been linked to both tectonics and climate cycles. Terrace aggradation took place in glacial and interglacial periods. The abandonment of terrace surfaces occurred both at warming transitions and in interglacial periods. New uplift rates calculated for the Pleistocene fluvial system suggest that tectonic activity in the Sorbas Basin has been episodic. The south margin and centre of the Sorbas Basin has uplifted at a faster rate than the northern margin impacting on the rates of incision taking place in the fluvial systems. Overall tectonic uplift has increased the fluvial system sensitivity to climatic variations.

This research is an integrated geological and geomorphological study into the Denton Hills area. The study area is part of the foothills to the Transantarctic Mountains, which divides East and West Antarctica, allowing an opportunity to investigate glacial events from both sides. As the study area is ice-free, it has allows good examination of the bedrock geology and has preserved geomorphological features allowing them to be examined and sampled. Comprehensive geological map and geomorphological maps have been produced, extending the knowledge into the spatial distribution of units and features. Both the geological and geomorphological maps reveal a complex history of evolution. The original geological units have been subjected to deformation and intrusion of large plutons. The geomorphological mapping shows ice has flowed in alternate direction through the valleys, and the valleys have had long periods where they have been occupied by large proglacial lakes. As the Antarctic ice sheets expanded they flowed into the valleys either from the west, the Royal Society Range draining the East Antarctic Ice Sheet or from the east, McMurdo Sound. Ice would flow from McMurdo Sound when the West Antarctic Ice Sheet expanded causing the grounding line of the ice sheet to move north through the Ross Sea. Surface exposure dating completed during the study has correlated the timing of glacial events to global cycles. The dating confirmed the presence of the large proglacial lake during the Last Glacial Maximum in the Miers Valley, which drained about 14 ka. The Garwood Glacier has also been directly linked to the Last Glacial Maximum with a moraine forming about 22 ka. The dating has also shown that during the Last Glacial Maximum there was little fluctuation in the size of glaciers draining the East Antarctic Ice Sheet, with features being date to the onset of the Last Glacial Maximum.

Lorsque l’extension de la croûte sous les parties hautes des chaînes de montagnes est colinéaire à la direction de convergence, il est traditionnellement admis que le moteur est l’effondrement gravitaire. Pourtant, des études récentes remettent en cause ce paradigme en montrant que l’érosion induit un soulèvement et de l’extension dans la partie centrale des chaînes de montagne à faible taux de convergence. L’objectif de notre étude est d’étudier l’impact de la dénudation de la topographie sur le régime sismo-tectonique des chaînes de montagnes.La première partie de ce travail présente une compilation de données dans les chaînes de montagnes afin de dégager des relations entre régime sismo-tectonique et érosion. Sur la base de ces observations, un modèle cinématique simple permettant de prévoir le régime de la chaîne est proposé. Ainsi, pour les chaînes à faible taux de convergence et d’élévation moyenne, ce modèle prédit de l’extension lorsque le taux de dénudation est 15% plus élevé que le taux de convergence.La deuxième partie est consacrée au développement d’un modèle thermo-mécanique 2D en éléments finis pour étudier l’impact des processus de surface sur la déformation des Pyrénées. Les résultats montrent que la réponse isostatique à l’érosion permet de réactiver des structures pré-existantes. La cinématique d’un plan de faille hérité peut être prédite grâce au gradient du profil des vitesses de surface horizontales. Ainsi, un plan situé dans la zone d’érosion est réactivé en faille normale alors qu’en bordure de cette zone une faille est réactivée en régime inverse. Ces résultats suggèrent que la déformation actuelle des Pyrénées pourrait être la conséquence d’un processus d’érosion.Compte tenu du faible nombre d’études quantifiant les taux d’érosion dans les Pyrénées, les modèles développés dans la deuxième partie souffrent d’une forte incertitude. Pour y remédier, nous avons cherché à les quantifier dans les Pyrénées Centrales grâce à une étude qui combine deux types de données : taux de dénudation des bassins versants à partir des isotopes cosmogéniques, et vitesses d’incision à partir des sédiments piégés dans les karsts). Ces résultats sont présentés dans la troisième partie. Les profils de dénudation obtenus sont compatibles avec un rejeu en faille normale d’un plan situé dans la Zone Nord Pyrénéenne des Pyrénées Centrales. Dans les Alpes, une bonne corrélation apparaît entre la valeur du taux d’érosion et la vitesse verticale géodésique, ce qui pose la question de l’impact de la déglaciation tardi-Wurmienne dans les Alpes sur la déformation actuelle. Un modèle numérique détaillant cette relation est présenté dans le quatrième chapitre. Les résultats montrent que la déglaciation des Alpes occidentales est contrôlée par l’hétérogénéité rhéologique de la croute. Certains de nos modèles prédisent des vitesses de surrection compatibles avec celles mises en évidence par la géodésie. / When mountain ranges upper parts express crustal extension direction collinear to the convergence direction, it is traditionally accepted that the extensive motor is gravitational collapse. However, recent studies challenge this paradigm by showing that erosion induces uplift and extension in the central part of the low convergent mountain ranges. Our goal is to investigate the impact of the denudation on the seismotectonic regime of mountain ranges.In order to identify a relationship between seismotectonic regime and erosion, the first part of this work presents a compilation of data in the mountain ranges. Based on these observations, a simple kinematic model is proposed to predict the seismotectonic regime of the chain. Thus, for low convergence rate chains with a moderate mean elevation, this model predicts an extension regime when the denudation rate is 15% higher than the convergence rate.The second part is devoted to the development of thermomechanical 2D finite element model to study the impact of surface processes on the deformation of the Pyrenees. The results show that the isostatic response to erosion reactivates pre-existing structures. The kinematics of an inherited fault plane can be predicted due to the gradient of the horizontal surface velocities profile. Thus, a plane located in the eroded zone is reactivated in normal fault when in a border area of this same plane is reactivated in reverse fault. These results suggest that the current deformation in the North Pyrenean Zone could be the result of surface processes.Given the small number of studies quantifying erosion rates in the Pyrenees, the models developed in the second part suffer from high uncertainty. To remedy this, we sought to quantify it in the central Pyrenees through a study that combines two types of data: watershed denudation rates from cosmogenic isotopes concentration, and incision rates from sediments buried in the karst. These results are presented in chapter 3. Denudation profiles obtained are consistent with a replay of a normal fault plane located in the North Zone of the Central Pyrenees.In the Alps, a good correlation appears between the value of the rate of erosion and geodetic vertical velocities, which raises the question of the impact of the late-würmian deglaciation in the Alps on the present deformation. A numerical model detailing this relationship is presented in the fourth chapter. The results show that deglaciation of the western Alps is controlled by the rheological heterogeneity of the crust. Some of our models predict uplift rates consistent with those highlighted by geodesy.

The New River crosses the core of the ancient, tectonically quiescent Appalachian orogen as it follows its course through North Carolina, Virginia, and West Virginia. It is ideally situated to record the changes in geomorphic process rates that occur in the Appalachians as a response to late Cenozoic climate variations. Active erosion features on resistant bedrock that floors the river at prominent knickpoints demonstrate that the river is currently incising toward base level. However, large packages of alluvial fill and fluvial terraces cut into this fill record an incision history for the river that includes several periods of stalled downcutting and aggradation. Cosmogenic 10-Be exposure dating, aided by mapping and sedimentological examination of terrace deposits, is used to constrain the timing of events in this history. Fill-cut and strath terraces at elevations 10, 20, and 50 m above the modern river yield cosmogenic exposure ages of approximately 130, 610, and 955 ka, respectively, but uncertainties on these ages are not well-constrained. This translates to a long-term average incision rate of 43 m/my, which is comparable to rates measured elsewhere in the Appalachians. During specific intervals over the last 1 Ma, however, the New River's incision rate reached 97 m/my. Fluctuations between aggradation and rapid incision appear to be related to late Cenozoic climate variations, though uncertainties in modeled ages preclude direct correlation of these fluctuations to specific climate change events. Erosion rates on higher alluvial deposits adjacent to the river are estimated from 10-Be concentrations; these rates are very low, about 2 m/my or less. This demonstrates a disequilibrium in the modern landscape, with river incision greatly outpacing erosion from nearby landforms. / Master of Science

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 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.

Ce travail de thèse est divisé en deux parties. La première porte sur l'acquisition d'un nouvel enregistrement paléosismologique en Mer de Marmara. Différentes méthodes ont été utilisées afin d'identifier et de caractériser les perturbations sédimentaires associées aux tremblements de terre dans les carottes étudiées. Nous avons cherché à acquérir une compréhension spatio-temporelle des distributions des séismes en mer pour aboutir à une meilleure compréhension du comportement de la Faille Nord Anatolienne sur le long terme. Nous avons par ailleurs cherché à corréler les données de sismicité historique avec de nouvelles données paléosismologiques. Les événements sédimentaires associés aux séismes ont été caractérisés en combinant l'imagerie aux rayons X, des mesures de susceptibilité magnétique, de granulométrie et de composition géochimique. Les données des compositions élémentaires nous ont permis de tracer au travers des différents bassins les changements environnementaux et anthropiques ayant lieu dans la région. L’obtention d’une chronologie robuste dans les carottes a également été recherchée en combinant des datations carbone 14 et des données de 210Pb et 137Cs afin de relier les sismoturbidites à la sismicité historique. Les variations d'aimantation au travers des carottes ont été mesurées dans le but initial de contraindre par une méthode indépendante l'âge des sédiments échantillonnés. Les variations des propriétés magnétiques ont mis en évidence une chute d'aimantation importante que nous avons reliée à des dépôts sapropéliques.La deuxième partie porte sur l’étude géomorphologique du décalage de la rivière Kizilirmak le long du segment central de la Faille Nord Anatolienne. À cet endroit, trois terrasses préservées le long de deux bassins en pull-apart incisés par la rivière Kizilirmak ont été cartographiées. Les résultats principaux de cette étude ont été de contraindre par la méthode des isotopes cosmogéniques 10Be, 26Al et 36Cl l'âge de ces terrasses. Les datations montrent que la terrasse la plus basse est âgée de 6 ka, que la deuxième terrasses est âgée de 50 ka et que la troisième a un âge de 80 ka. Cette dernière montre une contribution importante d'âges jeunes liée à l'érosion du bassin versant situé au-dessus d'elle. Les résultats montrent une origine climatique des terrasses et ont permis d'estimer une vitesse d'incision de la rivière de l'ordre de 3 mm/an depuis le début de l'Holocène. / This PhD work is divided in two parts. The first part focuses on obtaining a new paleoseismological record of earthquakes in the Marmara Sea (West of Turkey) using different analysis to pinpoint and characterize earthquake-related sedimentary disturbance in the studied cores. We seek to provide a spatio-temporal understanding of earthquakes in the Marmara Sea allowing greater insight into long-term fault behaviour and seismic interaction by integrating historical and new paleosismological data (recurrence rate in the Sea of Marmara). We characterized earthquake-related sedimentary events by combining X-ray imagery, magnetic susceptibility, granulometry and XRF (chemical analyses) measurements. Geochemistry data also allowed us to trace between basin anthropogenic and environmental changes occurring in the Marmara Sea. We also aim at establishing a reliable and robust chronology of the cores combining radiocarbon dating (bulk sedimentation, foraminifers, shelves), 210Pb and 137Cs data to connect seismoturbidites to historical seismicity. Magnetic variations were also recorded in the cores to obtain a time constrain for the cores. The down-core changes in magnetic properties suggest taking into account possible delays in the acquisition of magnetization and have been correlated to lower sapropelic layers in the Marmara Sea.The second part deals with geomorphology and tectonic in the central part of the North Anatolian Fault situated in Turkey. There, three terraces preserved in two pull-apart and incised by the longest river in Turkey (the Kizilirmak River) are mapped. The main results of this work are several constraints on the ages of the terraces using 10Be, 26Al and 36Cl cosmogenic dating methods. The obtained in situ cosmogenic 36Cl exposure ages calculated are 6 ka for the lowest terrace, 50ka for the middle terrace, and 80ka for the highest terrace in the areas preserved from erosion. The highest terrace shows a contribution of younger ages due to erosion of the nearby limestone catchment. The obtained results imply a climatic origin of the terraces, and a mean incision rate of about 3 mm/yr since the early Holocene along the Kizilirmak River.