The mechanism of Holocene barrier formation aids in determining island geomorphologic responses to modifying climatic processes of the surrounding environment. The geometry and composition of local antecedent topography plays a role in barrier formation by providing an elevated base, nucleus for sedimentation and local sediment supply. Investigation of barriers' subsurface geology provides insight into island formation and evolution. High-resolution shallow seismic data acquired in the island's nearshore zone and interior canals, correlated with existing drillcore data, reveal that Cat Island, MS is situated over an Oxygen Isotope Stage 3 Phase 3 paleochannel located between two topographic high-grounds of the Pleistocene surface. Beach ridge strandplain sets on Cat Island provide additional evidence supporting the island's formation over a relict depocenter. A new, 4-stage model for Cat Island development and evolution incorporating the influence of pre-existing topographic high-grounds and abundant local sediment supply provided by a backfilling fluvial channel is presented here.

Dendrochronological investigations on subfossil European ash (Fraxinus excelsior L.) wood found in two bogs of Western Lithuania are presented. Radiocarbon dating has revealed that Fraxinus grew in the Middle and Late Holocene, from approximately 4700 BC to 1500 BC. It is proposed that the growth of Fraxinus at these bogs was limited by differing hydrological regimes. Rising soil water levels induced a long decline in radial growth followed by a sharp reduction (up to 51%) in ring widths before the trees died. Until now, forest history in Lithuania was mostly based on results from palynological studies. This research demonstrates the potential of using dendrochronology to extend the distribution record of Fraxinus in the Baltic region during different periods of the Holocene.

Sous le prisme de la pluridisciplinarité, la dichotomie entre anthropisation et environnement s’est réduite à mesure que de fortes interrelations dans les seuils d’évolution ont été démontrées. Les vallées fluviales constituent des supports d’observation privilégiés des relations hommes-milieux, et de nombreux fleuves ont fait l’objet de ce type d’étude ces dernières années. Le choix de la Garonne s’est imposé face au vide scientifique qui caractérise une grande partie du tracé au sein du Sud-Ouest de la France, en particulier la section moyenne. Ce travail se concentre donc sur l’étude des relations entre le peuplement et la basse plaine entre Toulouse et la confluence du Tarn depuis 10000 ans. La vallée atteint 25km de large à Toulouse et correspond à la première zone d’étalement des crues pyrénéenne, favorable à l’enregistrement des occupations passées et de la dynamique alluviale qui les a accompagnés. En l’absence de référentiel local, un cadre chronologique géomorphologique et archéologique a été mis en place pour l’Holocène à partir des travaux réalisés sur différents cours d’eau européens et continentaux. Ces deux volets ont ensuite été analysés distinctement sur la plaine de la Garonne à l’aide d’une méthodologie pluridisciplinaire. Les résultats montrent que l’occupation de la plaine alluviale est continue depuis le Néolithique, malgré une restitution biaisée par les travaux d’aménagement modernes et la taphonomie. Cette dernière est marquée par une forte mobilité du chenal de la Garonne et l’identification d’au moins deux épisodes d’incision au cours du 2nd l’Holocène et une nette diminution de l’alluvionnement depuis l’Antiquité. / Through the prism of multidisciplinarity, the dichotomy between environment and human impacts is reduced as strong interrelationships in thresholds have been demonstrated. The valleys are favored supports of human-environnement relations, and many rivers have been the subject of this type of study in recent years. The Garonne’s choice result of a scientific blank in the most part of the channel in the South West of France, especially the middle section. Therefore this work focuses on the study of the relationship between human occupation and the low plain from Toulouse to the confluence of the Tarn since 10000 years. The valley is 25km wide in Toulouse and is the first Pyrenean flood spreading area, enabling the recording of past occupations and the alluvial dynamic associated. Without local repository, geomorphological and archaeological chronological framework was established for the Holocene, based on works completed in European and continental channels. These two component were analyzed separately on the plain of the Garonne river with a multidisciplinary approach. The results show that the floodplain’s occupation is continuous since the Neolithic, despite restitution biased by modern development works and taphonomy. This aspect is characterized by a high mobility channel f the Garonne and the identification of at least two episodes of incision in the 2nd Holocene and a net sedimentation decrease since Antiquity.

Thesis submitted in fulfilment of the academic requirements for the degree of Doctor of Philosophy School of Geography, Archaeology and Environmental Studies University of the Witwatersrand, Johannesburg October 2015 / The eastern Lesotho highlands observe climate patterns distinct from adjacent lower altitude regions, representing a niche environment with unique biodiversity, comprising well-adapted but restricted biomes. With a heavy reliance on subsistence agriculture, Lesotho faces risks to both the economy and individual livelihoods, should current rates of climate change persist or intensify. Furthermore, eastern Lesotho serves as southern Africa’s primary water catchment, with precipitation exceeding evaporation. Any changes in the climate and hydrological systems, as are likely under climate change scenarios, would compromise biomes, livelihoods, and water security both locally and regionally. Climate change research in eastern Lesotho, is thus of particular value, yet meteorological data are sparse and the palaeoenvironmental history remains poorly resolved. This research presents the first multi-proxy Holocene palaeoenvironmental and palaeoclimatic reconstruction for eastern Lesotho. This reconstruction is developed from the results from pollen, diatom and sediment analyses, extracted from sediment cores obtained from two peat bogs at Sani Valley (~2,800 m.asl) and Mafadi Wetland (~3,390 m.asl), and from an exposed gully-sidewall profile at Sekhokong (~2,950 m.asl), approximately 1km south of the Sani Valley site. The reconstructions are temporally constrained by AMS radiocarbon dates obtained for all three sites. Mafadi Wetland demonstrates marked differences to the lower altitude sites, including slower sedimentation rates, a decrease in pollen and diatom taxa diversity, and an increase in the relative abundance of ice-tolerant diatom taxa. The microtopography of the three sites influences the rates of sedimentation, sediment properties, pollen composition, and distinct palaeoenvironmental and palaeoclimatic reconstructions for each site. The Sekhokong record commences in the late Pleistocene, with a wet period from ~13,180-10,850 cal. yr BP, interrupted by a dry period from ~13,080-12,830 cal. yr BP. From ~10,550-6,420 cal. yr BP, the Sekhokong record indicates a drier climate with a slow transition to warmer, wetter conditions. The Mafadi Wetland record commences with cold, wet conditions from ~8,140-7,580 cal. yr BP, followed by a warmer, drier period from ~7,520-6,680 cal. yr BP. Thereafter, greater microclimatic differences are apparent. For Sekhokong, warmer, dry conditions are inferred for ~6,420-6,000 cal. yr BP, followed by cold, wet conditions from ~6,000-5,450 cal. yr BP. Warmer, dry conditions commence earlier at Mafadi Wetland, from ~6,160-5,700 cal. yr BP, coinciding with the initiation of a longer wet period at Sani Valley, from ~6,200-4,900 cal. yr BP. At Sekhokong, a dry, warmer period follows from ~5,450-3,700 cal. yr BP. At Sani Valley, drier conditions are evident from ~4,770-4,470 cal. yr BP, followed by a cold, wet period from ~4,460-2,260 cal. yr BP. For Mafadi Wetland, these cold, wet conditions endure longer, from ~5,600-1,100 cal. yr BP. This overlaps with similarly cool, wet conditions at Sekhokong, from ~3,650- 1,200 cal. yr BP. By contrast, dry conditions are evident at Sani Valley, from ~2,260-1,350 cal. yr BP. For all three sites, ~1,000 cal. yr BP to present is characterised by progressive drying, with discrete wet events. Pronounced cold events are detected at ~12,660 cal. yr BP, ~8,400-8,000 cal. yr BP and ~150 cal. yr BP. The results of this study indicate similarities with records from adjacent studies in western Lesotho and South Africa, although with notable variability in the timing of events. The palaeoenvironmental reconstructions for eastern Lesotho, and their comparison with existing studies, provide valuable information to improve the understanding of southern African Holocene climates, and to facilitate the development of high resolution, accurate climate models for the eastern Lesotho region.

Thesis advisor: Corinne I. Wong / Investigating controls on past variability of South American hydroclimate is critical to assessing its response to future warming scenarios. δ¹⁸O records from South America offer insight into past variability of the South American Monsoon System (SAMS). The controls on precipitation δ¹⁸O values, however, can be decoupled from precipitation amount and thereby limit investigations of variability in local moisture conditions. Here we use a principle components analysis to assess the coherence of speleothem and lake core Holocene δ¹⁸O records in tropical South America to evaluate the extent to which δ¹⁸O variability reflects changes in SAMS intensity at different sites across the region. The main mode of variability across Holocene δ¹⁸O records (PC1) closely tracks austral summertime insolation, consistent with existing work. PC1 is strongly expressed at sites towards the periphery of the continent, while variability at interior sites bear little similarity that implicates controls, in addition to monsoon intensity, on these δ¹⁸O records. Further, we develop speleothem ⁸⁷Sr/⁸⁶Sr records spanning the Holocene from Tamboril Cave (Brazilian Highlands), Paraíso Cave (eastern Amazon Basin), Jaraguá Cave (Mato Grosso Plateau), and Botuverá Cave (Atlantic coastal plain) to investigate coupling between reconstructed monsoon variability and local moisture conditions. Speleothem ⁸⁷Sr/⁸⁶Sr variability is interpreted as a proxy of local moisture conditions, reflecting the degree of water-rock interaction with the cave host rock as driven by variations in water residence time. Speleothem ⁸⁷Sr/⁸⁶Sr records from all the sites, except Botuverá cave, do not co-vary with PC1, suggesting that local moisture conditions do not necessary follow variations in monsoon intensity at these interior sites. These speleothem ⁸⁷Sr/⁸⁶Sr records, however, generally suggest dry mid-Holocene conditions, consistent with interpretations of other paleo-moisture records in the region. These results highlight that dynamics, in addition to SAMS variability, might influence δ¹⁸O variability as well as local moisture conditions at interior sites, and highlight the need for δ¹⁸O-independent reconstructions of moisture conditions. / Thesis (MS) — Boston College, 2018. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

O delta do rio Tubarão, situado na costa centro-sul catarinense entre os municípios de Tubarão, Jaguaruna e Laguna, constitui raro exemplo de delta lagunar ativo no Brasil. Sua planície deltaica cobre área aproximada de 250km2, onde são encontradas evidências de migração de canais fluviais dadas por séries de truncamentos de antigos distributários, alguns ainda ativos. Dez testemunhos foram obtidos junto aos principais canais distributários do rio Tubarão, a partir dos quais foram realizadas análises de fácies, granulométrica, de minerais pesados, de teor de matéria orgânica e de relações químio-isotópicas, além de datações 14C. Também foram levantados acervos históricos de fotografias aéreas e de dados de prospecção mineral de subsuperfície. Cerca de 5000 anos atrás, na região de seu ápice, próximo ao rio tributário Capivari de Baixo, o delta do rio Tubarão ingressou numa antiga baía lagunar e ramificou-se em sete distributários principais que, desde seus momentos iniciais de migração, foram controlados por avulsões autogênicas rumo a antigas depressões do fundo da bacia receptora. Tais avulsões progradaram o delta inicialmente para SW, depois para ENE, e então para NNE, favorecendo a fragmentação da antiga baía lagunar em uma série de lagos e lagunas menores. Diante deste cenário dinâmico, sambaquis foram erigidos no entorno do sistema lagunar, constituindo importantes registros arqueológicos de interação entre evolução sedimentar e ocupação humana pré-histórica. O resultado das análises granulométricas indicou que a sedimentação deltaica, nas proximidades de encostas de morros, foi misturada com colúvio e/ou depósitos de fluxos gravitacionais, como evidenciado pela presença de intervalos texturalmente muito imaturos em alguns testemunhos. Em relação à análise de minerais pesados, o principal fator de controle nas variações da assembleia em depósitos de delta e de bacia é a proveniência sedimentar. Em termos mediatos, essa proveniência reflete fontes plutônicas e metamórficas (médio a alto grau) do Batólito de Florianópolis (e xenólitos associados) e do Complexo Granito-Gnáissico, e rochas arenáceas alteradas da Bacia do Paraná. Em termos imediatos, depósitos deltaicos destacam-se pela afinidade mineralógica com as areias do rio Tubarão, inferida sobretudo a partir da presença mútua de grãos alterados de cianita e estaurolita, enquanto que depósitos da bacia lagunar destacam-se por sua similaridade mineralógica com areias dos rios tributários Braço do Norte e Capivari de Baixo, neste caso principalmente pela presença de zircão. A matéria orgânica presente nos depósitos do delta e de sua bacia receptora resulta do aporte de fontes terrestres (fornecido pelos rios) e marinhas (trazido via desembocaduras lagunares), fato que é evidenciado pelos resultados de \'delta\'\'POT.13 C\', \'delta\'\'POT.15 N\' e razão \'C IND.ORG\'/\'N IND.TOTAL\'. Particularmente, nos sedimentos da bacia, variações entre diferentes tipos de matéria orgânica têm ocorrido ao longo do Holoceno, as quais são atribuídas tanto ao isolamento físico progressivo do sistema lagunar em relação ao mar aberto como por mudança climática regional (aumento destacado de precipitação). A análise isotópica de oxigênio (\'delta\'\'POT 18 O\') de conchas de moluscos em depósitos da bacia indicou enriquecimento relativo em \'ANTPOT.16 O\' durante o Holoceno. Este resultado, a exemplo daquele dos isótopos de carbono e de nitrogênio dos sedimentos, sugere isolamento gradual das águas lagunares em relação às de mar aberto. / The Tubarão river delta, located on the centre-south coast of Santa Catarina State, among the municipalities of Tubarão, Jaguaruna and Laguna, is rare example of active lagoonal delta in Brazil. Its delta plain covers an area of about 250km2, where there are evidences of migration of fluvial channels in a set of truncations of ancient distributaries, some of these still in activity. Ten cores were acquired adjacent to the main distributary channels of the Tubarão river, from which analyses of facies, grain size, heavy minerals, organic matter, chemistry-isotope ratios, and radiocarbon datings were performed. Also, aerial photographies and data of subsurface mining were surveyed from historical collections. Thereabout 5,000 years ago, in the region of its apex, near Capivari de Baixo tributary river, the Tubarão river delta entered an ancient lagoonal bay and branched seven main distributaries. Since the beginning of its migration, these distributaries were controlled by autogenic avulsions towards ancient depressions in the bottom of the basin. Initially, these avulsions prograded the delta towards SW, afterwards to ENE, and then to NNE, favoring the fragmentation of the ancient lagoonal bay in a set of smaller lakes and lagoons. Faced with this dynamical scenario, shellmounds were erected surrounding the lagoon system, composing important archaeological records of the interaction between sedimentary evolution and prehistoric human occupation. The results of the grain size analysis showed that the deltaic sedimentation, in the vicinity of slopes of hills, was mixed with colluvium and/or gravity flow deposits, that is evidenced by the presence of texturally very immature intervals in some cores. The analysis of heavy minerals, by its turn, showed that the main controlling factor in the variations of its assemblage in deposits of delta and basin is the sedimentary provenance. In terms of mediate sources, this provenance reflects plutonic and metamorphic (medium to high grade) rocks of the Florianópolis batholith (including its xenoliths) and of the Granite-Gneiss Complex, and weathered sedimentary sandstones of the Palaeozoic Paraná basin. Regarding immediate sources, deltaic deposits stand out by its mineralogical affinity with sands of the Tubarão river, mainly by the mutual presence of weathered grains of kyanite and staurolite, whereas deposits of the lagoon have mineralogical similarity with the sands of Braço do Norte and Capivari de Baixo tributary rivers, especially in relation to the presence of zircon. The origin of the organic matter found in the deposits of the delta and in its lagoonal basin is both from sedimentary input of terrestrial sources (provided by rivers) and marine (brought via inlets), fact evidenced by results of \'delta\'\'POT.13 C\', \'delta\'\' POT.15 N\', and \'C IND.ORG\'/\'N IND. TOTAL\' ratio. Particularly, in the sediments of the basin, variations between different types of organic matter have occurred during the Holocene, and are attributed both to the progressive physical isolament of the lagoon system from the open sea, and by local climate change (pronounced augment of precipitation). The isotope analyses of oxygen (\'delta\'\'POT.18 O\') of molluskan shells from the deposits of the basin present relative enrichment in \'ANTPOT.16 O\' during the Holocene. This result, as well as the one from isotope analyses of carbon and nitrogen of sediments, suggests gradual isolation of the lagoonal waters of influence of waters from the open sea.

O presente estudo foi desenvolvido em uma turfeira localizada no baixo curso do rio Ribeira de Iguape, Litoral Sul de São Paulo com o objetivo de reconstituir os paleoambientes e as possíveis variações ambientais ocorridas na área por meio da análise de palinomorfos e das características dos sedimentos do testemunho de sondagem de 520 cm de profundidade. A análise de bio e geoindicadores permitiu reconstituir parte da história de evolução sedimentar holocênica da área. Para isso a análise foi fundamentada sob o ponto de vista da biogeografia, envolvendo a interpretação e correlação entre as variáveis: sedimentológicas, espongológica, foraminíferos, palinológicas e isótopos de 13C. Antes de 7.300 anos cal AP as características sedimentológicas evidenciam o início da sedimentação da planície de inundação onde foi depositado espículas de esponjas continentais de O. navicella, é provável que o aporte de água doce na área de estudo tenha causado o desaparecimento de espécies de foraminíferos, tecamebas e ostracodes pela dissolução das carapaças em águas com pH ácidos, o mesmo aporte que pode ter lixiviado o material polínico, pois os sedimentos são arenosos. Os elementos isotópicos com valores de -27,6 evidenciam que a matéria orgânica é de origem fluvial. Por volta de 7.300 anos AP (fácies 430 cm) o NRM cruzou o zero pela primeira vez no Holoceno. Essa interpretação é corroborada pela chegada de espículas de origem marinha nos sedimentos. Além disso, no nível de 430 cm observa-se redução da concentração de esponjas de água doce. Os valores de 13C - 25,9 indicam que a origem da matéria orgânica é mista. Entre 7.200 e 6.430 anos cal AP ocorreu novamente uma rápida regressão do NRM verificado pela presença frequente de esponjas continentais e raríssima presença de espículas marinhas. A área era colonizada por plantas típicas de ambientes sob influência marinha e fluvial como Asteraceae, Poaceae, Araceae, Begoniaceae, Ulmaceae, Arecaceae Bactris sp. (encontrada em áreas alagadas e/ou FPa). Antes de 6.430 anos cal AP ocorre o início da segunda e mais duradoura fase de transgressão marinha caracterizada pela espongofácies marinha e pela queda nas porcentagens de todos os táxons polínicos. O pico da transgressão ocorre antes de 5.124 anos cal AP nesse momento foi depositado material espicular marinho e continental evidenciando o ambiente estuarino, onde plantas herbáceas adaptadas a esse ambiente ainda colonizavam essa área com concentrações como Amaranthaceae. Posteriormente, o NRM decai lentamente chegando ao nível zero atual, aqui as porcentagens de espículas marinhas decaem paulatinamente até a profundidade de 225 cm. Por volta de 3.200 anos cal AP (médias das idades de 145 cm) o ambiente já se comportava como um pântano, há aumento na concentração de Bignoneaceae (Tabebuia), Cluseaceae (Clusia) e novamente Amaranthaceae sugerem a colonização de FPa. Plantas do gênero Tabebuia sp. destacam-se por se agruparem em áreas alagadas. Posteriormente, o aumento significativo nas concentrações polínicas de todos os táxons, principalmente dos indicadores de FPaT, indicam o desenvolvimento dessa formação vegetal. Devido à complexidade desse ambiente por causa de sua morfodinâmica há necessidade de cuidados na interpretação dos resultados, pois os registros de mega-eventos podem ser confundidos, mascarar ou levar as interpretações paleoambientais inadequadas. Por isso, o uso de multiindicadores e o conhecimento dos processos mostraram-se fundamentais e foi possível obter uma excelente resposta. / This study was developed in a peat bog located on the lower course of Ribeira river, South Coast of Sao Paulo, in order to reconstruct the paleoenvironments and possible environmental changes occurred in the area through analysis of palynomorphs and the characteristics of the sediments drill core depth of 520 cm. The analysis of bio and geoindicators allowed to reconstruct a part of the history of the Holocene sedimentary evolution of the area. The analysis was based on the point of view of Biogeography, involving the interpretation and correlation between variables: sedimentological, belong sponge, foraminifera, pollen and 13C isotopes. Before 7300 cal years BP the sediment characteristics show the beginning of sedimentation of the floodplain where it was deposited spicules of sponges continental O. navicella, it is likely that the freshwater inflow in the study area has caused the disappearance of species of foraminifera, ostracods and thecamoebian by dissolving the shells in waters with acidic pH, the same approach that may have leached the pollen material, because the sediments are sandy. The isotopic elements with values of -27.6 show that the organic matter is of fluvial origin. Around 7300 years BP (430 cm depth) NRM crossed zero for the first time in the Holocene. This interpretation is corroborated by the presence of spicules in the sediments of marine origin. Furthermore, at the level of 430 cm was observed a reduction of the concentration of freshwater sponges. 13C values of -25.9 indicate that the source of the organic matter is mixed. From 7200 until 6430 years cal AP occurred a rapid regression of NRM verified by the frequent presence of continental sponges and extremely rare presence of marine spicules. The area was colonized by plants typical of marine and fluvial environments under influence like Asteraceae, Poaceae, Araceae, Begoniaceae, Ulmaceae, Arecaceae Bactris sp. (found in flooded and / or FPa areas). Before 6430 years cal AP occurred the beginning of the second and more lasting phase of marine transgression characterized by marine espongofácies and for the decreased in percentages of all pollen taxa. The peak transgression occurs before 5124 years cal AP, when was deposited marine and continental espicular materials evidencing the estuarine environment, where herbaceous plants adapted to this environment yet colonized this area with concentrations as Amaranthaceae. Subsequently, the NRM decays slowly coming to the current zero level. Here the percentages of marine spicules decay gradually to a depth of 225 cm. Around 3200 cal years BP (mean ages of 145 cm) the environment has behaved like a swamp, there is an increase in the concentration of Bignoneaceae (Tabebuia), Cluseaceae (Clusia) and again Amaranthaceae suggest colonization of FPa. The genus Tabebuia sp. stands out for getting together in wetlands. Later, the significant increase in the pollen concentrations of all taxa, especially indicators of WPF, indicates the development of this plant formation. Due to the complexity of this environment because of their morphodynamics, caution is necessary in interpreting of the results because the records of megaevents can be confused, to mask or take inadequate paleoenvironmental interpretations. Therefore, the use of multi-indicators and the knowledge of the process were essentials and it was possible to obtain excellent response.

Effusive volcanic eruptions repave landscapes rapidly with lava flows, resetting the underlying landscape and ecosystem. The unique physical properties of lava pose interesting challenges for recovery, as lava flows can be highly permeable while lava itself is dense, sterile, and generally inhospitable towards life. This dissertation examines two aspects of landscape recovery following lava flow emplacement: (1) hydrologic adaptation of surface and groundwater to recent volcanism and (2) plant colonization of young lava flows. I examine two sites in the central Oregon Cascades: the c. 3 ka Sand Mountain volcanic field (SMVF), located in the headwaters of the McKenzie River, a critical water resource for the state of Oregon, and the c. 1.5 ka Collier Cone lava flow, originating on the north flanks of North Sister volcano. My investigation of the SMVF and upper McKenzie River watershed reveals a complex volcanic history with profound impacts on the configuration and short-term discharge of the McKenzie River: lava flows from the SMVF and other Holocene vents have buried, dammed, and altered the path of the McKenzie River. Moreover, given the large groundwater contribution from the SMVF to the McKenzie River, I estimate that SMVF activity caused McKenzie River discharge in present-day Eugene, Oregon to decrease by up to 20% for days to months at a time; future regional mafic volcanic activity could have a similar impact. The SMVF and the Collier Cone lava flow are notable for the juxtaposition of barren exposed lava and mature forests on the same or similarly aged lava flows. I use a combination of LiDAR analysis, field observations, and soil characterization to examine soil and vegetation at these two sites and find that the presence of an external soil source greatly facilitates plant establishment, growth, and survival. Here, external soil sources are syn- or post-eruptive tephra (SMVF) or flood-borne deposits (Collier Cone lava flow). External soil appears to provide a substrate for plants to grow in along with key nutrients and sufficient moisture; overall, external soil sources are key for the initial recovery following an effusive volcanic disturbance. This dissertation includes co-authored material submitted for publication.

Cette thèse propose de reconstituer l'histoire environnementale holocène du plateau du Béage en Ardèche (massif duMézenc, Massif Central, France). Ce travail repose sur l'étude des sédiments issus des tourbières de La Narce du Béage et de Pialeloup, mais aussi du marais de Pré-du-Bois et des séquences de la moyenne vallée du Gage. Notre approche vise (1) à caractériser le contenu paléoécologique des sédiments (macro-restes et palynologie), (2) à appréhender les évolutions du bassin versant via une analyse multi-proxies (susceptibilité magnétique, granulométrie,taux de matière organique, géochimie) et (3) à confronter ces éléments aux données locales et régionales disponibles.Durant !'Holocène ancien et moyen, des fluctuations locales d'humidité paraissent concomitantes de changements climatiques majeurs dans l'hémisphère nord (épisodes humides: 10400-10000, 9600-9100, 7900-7400, 6400-6000,5400-5000 cal. BP; secs: 10900-10500, 9900-9600 cal. BP; contrasté: 8500-8150 cal. BP). Cette analyse montre des impacts agro-pastoraux entre 6900 et 6450 cal. BP (Néolithique ancien), entre 5700 et 5200cal. BP (Néolithique moyen 2/récent) puis vers 4800 - 4100 cal. BP (Néolithique final). La pression anthropique s'intensifie entre 2400 et 1250 cal. BP (IVème s. av. J.-C.-Vlème s. apr. J.-C.). Le développement agricole médiéval s'opère à partir de 1050 cal. BP (Xème s.) : culture du seigle, cheptel ovin et bovin, productions de noix et de châtaignes à partir des XIIIème et XIVème s. L'érosion des versants semble aussi stimulée par la péjoration du Petit Âge Glaciaire (Xlllème-XVIIIème s.).Aux XIXème et XXème siècles, les activités d'élevage bovin perdurent mais la céréaliculture finit par disparaître. / This PhD thesis has resulted in the reconstruction of the holocene environmental history of the Béage plateau in Ardèche (massif du Mézenc, Massif Central, France). It focussed on the study of organic sediments from the La Narce du Béage and Pialeloup peatlands. Two complementary sites were also considered: the Pré-du-Bois swamp and the alluvial stratigraphies from the middle Gage valley. Our approach aimed (1) to perform a palaeoecological study of these sites (macrofossils and palynology); (2) to better understand watershed evolution thanks to multi-proxies analyses (magnetic susceptibility, grain size, organic matter content, geochemistry); (3) to compare these results with other local to regional data. During the Barly and the Middle Holocene, local humidity variations occuned concurrently with rapid climate changes(RCCs) recorded in the Northern Hemisphere (dry episodes: 10,900-10,500; 9,900-9,600; moist: 10,400-10,000;9,600-9,100; 7,900-7,400; 6,400-6,000 and 5,400-5,000 cal. BP; contrasted: 8,500-8,150 cal. BP). This study also allowed to identify agro-pastoral impacts around 6,900-6,450 cal. BP (Barly Neolithic), around 5, 700-5,000 cal. BP (Middle to Recent Neolithic) and close to 4,800-4,100 cal. BP (Final Neolithic). Anthropogenic impact got stronger between 2,400 and 1,250 cal. BP (IV'h century BC-Vlth century AD). A new stage of landscape management was recorded after 1,050 cal. BP (Xth century AD), involving rye cultivation, extensive livestock grazing(sheep and cattle) and fruit tree farming (walnut and chestnut: XIIIth-XIV'h centuries). Severe soil erosion occurred, alsodriven by the Little Ice Age deterioration (from the XIIlth to the XVth century AD). Finally, during the X!Xth and theXXth centuries cattle grazing remained strong, but cultivation ended due to demographic exodus during the xxth century.

The northern slopes of the Uinta Mountains, Utah were previously glaciated and contain many landslides. The Tokewanna Landslide is very large and lacks Quaternary faults. Presumably, increased moisture was the failure trigger. A Quaternary climate record from a cored fen, developed in a small basin between hummocks, was reconstructed using sediment pyrolysis, biomass balance, and magnetic susceptibility. Pyrolysis is used to define Hydrogen Indices that are used to delineate wetter and drier conditions based on the kerogen type - Type III being drier, and Type II wetter. The data were matched to a time/depth curve and compared to other Uinta Mountains climate studies. Pyrolysis, biomass balance, and magnetic susceptibility results indicate drier to wetter conditions from ~11,027 to ~8,800 cal yr BP. This was followed by an increase in precipitation, peaking ~8,060 cal yr BP, and then decreasing. Drying conditions ensued after ~4,800 cal yr BP, and from ~1,700 cal yr BP to modern. Regional studies suggest mid-Holocene Epoch warming; some also indicate increased precipitation during those periods. A study at nearby Little Lyman Lake (Tingstad et al., 2011) displays a plankton percent record similar to the wetness record of the study fen. The fen core record does not indicate wet conditions at its base as expected. The record begins ~11,000 cal yr BP and likely represents an incomplete history of this Holocene fen, as the base of the wetland deposits was not reached.