abstract: For this dissertation, three separate papers explore the study areas of the western Grand Canyon, the Grand Staircase (as related to Grand Canyon) and Desolation Canyon on the Green River in Utah. In western Grand Canyon, I use comparative geomorphology between the Grand Canyon and the Grand Wash Cliffs (GWC). We propose the onset of erosion of the GWC is caused by slip on the Grand Wash Fault that formed between 18 and 12 million years ago. Hillslope angle and channel steepness are higher in Grand Canyon than along the Grand Wash Cliffs despite similar rock types, climate and base level fall magnitude. These experimental controls allow inference that the Grand Canyon is younger and eroding at a faster rate than the Grand Wash Cliffs. The Grand Staircase is the headwaters of some of the streams that flow into Grand Canyon. A space-for-time substitution of erosion rates, supported by landscape simulations, implies that the Grand Canyon is the result of an increase in base level fall rate, with the older, slower base level fall rate preserved in the Grand Staircase. Our data and analyses also support a younger, ~6-million-year estimate of the age of Grand Canyon that is likely related to the integration of the Colorado River from the Colorado Plateau to the Basin and Range. Complicated cliff-band erosion and its effect on cosmogenic erosion rates are also explored, guiding interpretation of isotopic data in landscapes with stratigraphic variation in quartz and rock strength. Several hypotheses for the erosion of Desolation Canyon are tested and refuted, leaving one plausible conclusion. I infer that the Uinta Basin north of Desolation Canyon is eroding slowly and that its form represents a slow, stable base level fall rate. Downstream of Desolation Canyon, the Colorado River is inferred to have established itself in the exhumed region of Canyonlands and to have incised to near modern depths prior to the integration of the Green River and the production of relief in Desolation Canyon. Analysis of incision and erosion rates in the region suggests integration is relatively recent. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2016

Les modalités d’évolution d’une côte rocheuse granitique en contexte de marge passive restent encore mal connues à ce jour, du fait de leur évolution lente. L’objectif de l’étude du littoral granitique du sud-Finistère vise à mieux comprendre son développement et sa dynamique érosive sur une échelle de temps variant entre le Cénozoïque et le Quaternaire. Une cartographie Terre-Mer de détail a permis d’identifier plusieurs objets morphologiques : une rasa (≈15m), une terrasse marine (≈7m), une plateforme littorale (0-5m) et une plateforme rocheuse sous-marine (-70 à 0m). Ces objets témoignent de la variabilité spatiale et temporelle des processus tectoniques vs. eustatiques sur le littoral breton. L’architecture 3D de la zone révèle une plateforme rocheuse sous-marine très fracturée avec de grands accidents délimitant plusieurs micro-blocs et fonctionnant au Cénozoïque (compression pyrénéenne éocène, puis ouverture Atlantique Oligocène et extension au post-Oligocène avec l’ouverture continentale des grabens du Rhin). La Pointe SO de la zone d’étude se stabilise durant le tardi-Cénozoïque, révélant que les figures d’érosion aériennes (rasa et terrasse marine) ont été générées lors de plusieurs paléo-haut niveau marin. Les larges surfaces des objets terrestres s’expliquent par l’action combinée des purges eustatiques sur un matériel granitique très altéré. Il a été démontré que la morphologie de la zone littorale granitique a été façonnée a minima par deux épisodes de purges eustatiques durant le MIS 5 (120ka) et l’Holocène (10ka). Les taux d'érosions verticaux obtenus pour la terrasse marine et la plateforme littorale varient entre 3.35 ±0.32 m.Ma-1 et 6.20 ± 0.80 m.Ma-1. / The granitic rocky coast evolution, in passive margin context, is still not completely understood as its evolution is lower. The aim of the South-Finistère shore zone studying is to better understand its development and erosive dynamic on a time scale ranging between Cenozoic and Quaternary. A detailed onshore/offshore mapping has been realized, highlighting several erosional features. From land seaward, a rasa (≈15m-high), a marine terrace (≈7m-high), a shore platform (0-5 m-high) and a rocky marine platform (-70 à 0m) have been emphasized. These objects evidence temporal variations in the response of the tectonic or eustatic processes. The 3D architecture of rocky marine platform demonstrates a highly fractured domain with major faults bounding several micro-blocks, reactivated between the Eocene (Pyrenean compression) and Late / Post-Oligocene (Rhine continental transform zone activation). The quantitative geomorphology applied on the western part of studying zone reveals none late-Cenozoic uplift. Consequently, the rasa and marine terrace have been shaped during a high paleo-sea level. The granitic surface’s erosion produces horizontal joint planes, as a result of weathering processes. The combination between planar and horizontal granitic jointing and the marine eustatic purge explains the large width of granitic eroded surfaces.Two eustatic purges (MIS 5 and Holocene) have been shaped the granitic shore zone and the vertical erosion, rate obtained for various lateritic horizon in onshore and shore domains, is ranging between 3.35 ±0.32 m.Ma-1 and 6.20 ± 0.80 m.Ma-1.

Idades de soterramento de grãos de quartzo pelos isótopos cosmogênicos \'ANTPOT.26 Al\' e \'ANTPOT.10 Be\' foram obtidas em depósitos sedimentares que assorearam os sistemas de cavernas associados aos vales cegos dos riachos das Almas e Água de Rega, região de Iraquara (BA). Os resultados também incluem a caracterização faciológica e uma abordagem preliminar sobre a arquitetura dos depósitos, além do mapeamento em campo do contexto geomórfico dos sistemas de condutos e seu preenchimento sedimentar. Coberturas terciárias assentadas sobre todas as unidades pré-cambrianas testemunham que a superfície cárstica e os sistemas de condutosfazem parte de uma longa história de evolução, envolvendo episódios de exposição, soterramento e exumação. Durante os dois últimos milhões de anos, a drenagem superficial e os sistemas de cavernas estavam plenamente articulados na condução de água e sedimentos, com rotas de fluxo subterrâneas que incluíam ainda trechos labirínticos pré-existentes, que serviam de repositório de sedimentos durante os eventos de inundação, proporcionando também, rotas alternativas ao canal,na medida em que o sistema agradava. A sucessiva migração do canal por estas redes labirínticas originou o padrão distributário observado na Lapa Doce e na Gruta da Torrinha. Os depósitos sedimentares estudados nas cavernas dividem-se em dois grupos: fluviais e de água estagnada. Osdepósitos fluviais ocorrem na base e são constituídos por fácies de canal e fácies de inundação. As idades de soterramento de grãos de quartzo destes sedimentos apontam para um período de assoreamento fluvial compreendido entre 1,91±0,12 e 0,36±0,08 milhões de anos para o sistema Lapa Doce-Torrinha (riacho Água de Rega) e 1,37±0,15 e 0,87±0,17 milhões de anos para o sistema Cão-Talhão (riacho das Almas). No sistema Lapa Doce-Torrinha as idades de soterramento concentram-se no intervalo compreendido por dois períodos úmidos (350-450 Ka e 900-1000 Ka), registrados em estudos anteriores através do crescimento de tufas calcárias no semiárido baiano.Tal fato sugere que a agradação fluvial verificada, tanto nos rios quanto nas cavernas, esteja associada a fatores climáticos, particularmente o aumento da carga dos rios derivado da diminuição na estabilidade dos grãos nas vertentes exercida por uma vegetação arbustiva esparsa ou ausente. No topo, os depósitos de água estagnada, preferencialmente compostos por lamas, não possuem estruturas trativas ou de corrente e são associados a uma sedimentação em ambiente freático,para o qual é necessário considerar a subida do nível de base. Gretas de contração, além de relações estratigráficas e erosivas destes depósitos com crostas calcíticas evidenciam que eles não foram depositados em um evento único. Idades U/Th obtidas nas crostas calcíticas apontam para uma deposição durante o Pleistoceno Tardio. Interpreta-se que as lamas foram depositadas durante períodos de elevação do nível de base devido aos eventos úmidos abruptos de escala milenar que ocorreram no nordeste brasileiro ao longo dos últimos 210 ka. / \'ANTPOT.26 Al\' and \'ANTPOT.10 Be\' burial ages have been obtained from quartz grains sampled in extensive sedimentary deposits that fill cave systems associated with Das Almas and Agua de Rega creeks blind valleys, Iraquara region, Bahia (Brazil). The geomorphic context of the caves and their sedimentary record is presented, as well a facies analyses and a preliminary architecture approach for subterranean deposits. Tertiary covers deposited over all Precambrian geological units give evidence that karstic surface and conduit systems are features of a long term evolving landscape, sculpted during episodes of exposure, burial and exhumation. In the last two million years, surface drainage and cave systems were full connected in terms of water and sediment transport.Conduit systems still connected with preexisting passage networks, working as sediment repositories during floods and offering alternative routes to the channels as the systems aggraded. Sucessive channel migration led to the distributary pattern observed in the caves Lapa Doce and Gruta da Torrinha. The cave sedimentary record can be divided into two major categories: alluvial and slackwater deposits. At the bottom of the sediments, channel and flood facies were recognized in alluvial deposits. Quartz simple burial ages point to fluvial aggradation between 1,91±0,12 and 0,36±0,08 My in Lapa Doce-Torrinha cave system (Água de Rega creek) and between 1,37±0,15 and 0,87±0,17 million years in Cão-Talhão cave system (Das Almas creek). Burial ages from Lapa Doce-Torrinha samples group in between two past humid periods (350-450 Ky and 900-1000 Ky) recorded in previous studies from travertines growth in arid regions of Bahia State. This fact suggests that valley and cave aggradation is associated with climate factors, particularly an increase in river load derived from decreased stabilization of hillslopes due to a sparse or absent forest vegetation. At the top of sedimentary pile slackwater deposits are ordinarily muddy without tractive or current sedimentary structures. They are assigned to be deposited in a phreatic environment which, in turn, necessarily requires the base level to rise longer than seasonal floods. Mud cracks, erosive surfaces and stratigraphic relations to calcite crusts and flowstones prove that they were not deposited in a single event. U/Th ages from interstratal calcite crusts point to mud deposition during the Late Pleistocene. Slackwater deposits are interpreted to be a result of sedimentation during successive abrupt wet events defined on millennial time scale for the Brazilian northeast during the last 210ky.

Ongoing retreat of Antarctica’s marine-based glaciers is associated with warm (~2° C) modified Circumpolar Deep Water intrusion onto the continental shelf, suggesting that Southern Ocean temperatures may influence Antarctic ice sheet stability. Understanding past cryosphere response to environmental forcing is crucial to modeling future ice sheet behavior. Of particular interest is the response of the East Antarctic Ice Sheet (EAIS), which stands to contribute ~20 m to global sea level. However, marine sediment sequences recording timing and variability of EAIS fluctuations through the last major climate shift, the Last Glacial Maximum (LGM), are either missing from the margin or have poor chronological control. Here we present three marine sediment cores that contain a record of pre-LGM fluctuations of the marine-based Lambert Glacier-Amery Ice Shelf (LG-AIS) system into Prydz Channel, East Antarctica. Analyses of core lithology, physical properties, cosmogenic nuclide concentration and diatom assemblage demonstrate that Prydz Channel was characterized by alternating open-marine and sub-shelf deposition, implying repeated LG-AIS fluctuations through the LGM. Our radiocarbon chronology demonstrates that LG-AIS fluctuations occurred on millennial timescales. Our record corroborates regional marine and terrestrial records, which demonstrate millennial scale variability in Antarctic Circumpolar Current strength, ice-rafted debris deposition, sea ice extent, Antarctic atmospheric temperature, and Southern Ocean sea surface temperature. This evidence suggests that the EAIS was sensitive to sub-orbital climate forcing in the past, and has implications for modeling future EAIS behavior.

Le flux de météorites vers la Terre peut être déterminé en observant des bolides, ou en étudiant des collections de météorites. Pour estimer l’intensité et la composition du flux, nous avons collecté et classifié une collection de 213 météorites issues du désert de l’Atacama (Chili). Nous avons développé un protocole chimique afin d’extraire des nucléides cosmogéniques de chondrites ordinaires. La fraction métallique est d’abord séparée de la météorite. Les échantillons sont ensuite dissouts dans l’acide, et les éléments utiles sont extraits et purifiés grâce à des résines échangeuses d’ions et des précipitations contrôlées. Après la mesure par SMA, les concentrations de nucléides cosmogéniques nous permettent de calculer l’âge terrestre, le rayon pré-atmosphérique et la profondeur dans le météoroide, en utilisant l'approche développée par Leya & Masarik (2009). En combinant le nombre de météorites par unité de surface et les spectres d’âge terrestre, nous pouvons déterminer un flux de 218 météorites>10g/Ma/km2 sur une période de 700 ka avec la méthode 41Ca.Dans le cadre d’une collaboration avec l’Université de Bern (Suisse), nous avons aussi mesuré les concentrations en gaz rares dans certaines de ces météorites. Les concentrations en gaz rares et en nucléides radiogéniques ont ensuite été étudiées avec le modèle développé par Ammon et al. (2009), afin de déterminer le temps d’exposition dans l’espace, l’âge terrestre, le rayon pré-atmosphérique et la profondeur dans le météoroide. / Meteorite flux to the Earth can be determined using observations of fireballs or studying meteorites collections. To estimate the intensity and the composition of the flux, we collected and classified a 213 samples collection from the Atacama desert (Chile). We developed a mathematical model to help pairing of meteorites, and hence get a reliable number of falls per unit of surface. A chemical procedure to extract the cosmogenic nuclides 10Be, 26Al, 36Cl and 41Ca from ordinary chondrites was developed. The metallic fraction was extracted from the bulk meteorite. Samples were dissolved into acid and the elements of interest were extracted and purified using ion-exchange resins and pH controlled precipitation. After measurements using the Accelerator Mass Spectrometry (AMS) technique, the cosmogenic nuclides concentrations enable us to calculate terrestrial age, pre-atmospheric radius and shielding depth, using the Leya & Masarik (2009) model. Combining the number of meteorites per km2 and the terrestrial ages spectrum, we determine a flux of 218 meteorites > 10g/Ma/km2 over 700 ka with the 41Ca calculation method. Applying the same procedure as described above, we studied a selection of iron meteorites in which noble gases (He, Ne and Ar isotopes) concentrations were measured in collaboration with the University of Bern (Switzerland). Stable and radiogenic nuclides concentration results were then used according to the Ammon et al. (2009) model to determine Cosmic Ray Exposure (CRE) ages, terrestrial ages, pre-atmospheric radii and shielding depths.

Thesis advisor: Jeremy D. Shakun / Glaciers in the tropics have undergone significant retreat in the past several decades, but the magnitude of this retreat in the long-term context of the Holocene has mostly been qualitatively assessed. This study produces a quantitative reconstruction of Holocene glacier extent relative to today from the Quelccaya Ice Cap, Peru, and the Rwenzori Mountains of east Africa. I use measurements of in situ 14C and 10Be from bedrock that was recently exposed by glacier retreat to constrain possible bedrock exposure and erosion histories at each site. The results are strikingly similar in both areas, and suggest that ice was generally smaller than today during the first half of the Holocene and larger than today for most, if not all, of the last several millennia. These findings give evidence toward a coherent Holocene expansion of glaciers across the tropics, and suggest that recent retreat is unusual in a multi-millennial context. / Thesis (MS) — Boston College, 2018. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22264号 / 理博第4578号 / 新制||理||1657(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)准教授 松四 雄騎, 教授 千木良 雅弘, 教授 岩田 知孝 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Antarctic debris-covered glaciers are potential archives of long-term climate change. However, the geomorphic response of these systems to climate forcing is not well understood. To address this concern, I conducted a series of field-based and numerical modeling studies in the McMurdo Dry Valleys of Antarctica (MDV), with a focus on Mullins and Friedman glaciers. I used data and results from geophysical surveys, ice-core collection and analysis, geomorphic mapping, micro-meteorological stations, and numerical-process models to (1) determine the precise origin and distribution of englacial and supraglacial debris within these buried-ice systems, (2) quantify the fundamental processes and feedbacks that govern interactions among englacial and supraglacial debris, (3) establish a process-based model to quantify the inventory of cosmogenic nuclides within englacial and supraglacial debris, and (4) isolate the governing relationships between the evolution of englacial /supraglacial debris and regional climate forcing. Results from 93 field excavations, 21 ice cores, and 24 km of ground-penetrating radar data show that Mullins and Friedman glaciers contain vast areas of clean glacier ice interspersed with inclined layers of concentrated debris. The similarity in the pattern of englacial debris bands across both glaciers, along with model results that call for negligible basal entrainment, is best explained by episodic environmental change at valley headwalls. To constrain better the timing of debris-band formation, I developed a modeling framework that tracks the accumulation of cosmogenic 3He in englacial and supraglacial debris. Results imply that ice within Mullins Glacier increases in age non-linearly from 12 ka to ~220 ka in areas of active flow (up to >> 1.6 Ma in areas of slow-moving-to-stagnant ice) and that englacial debris bands originate with a periodicity of ~41 ka. Modeling studies suggest that debris bands originate in synchronicity with changes in obliquity-paced, total integrated summer insolation. The implication is that the englacial structure and surface morphology of some cold-based, debris-covered glaciers can preserve high-resolution climate archives that exceed the typical resolution of Antarctic terrestrial deposits and moraine records.

Indiana University-Purdue University Indianapolis (IUPUI) / Subglacial chemical processes in Antarctica are potentially significant contributors to global geochemical cycles, but current understanding of their scale and nature is limited. A sequential chemical extraction procedure was developed and tested to investigate the utility of meteoric 10Be as a tracer for chemical weathering processes beneath the East Antarctic Ice Sheet. Subglacial meltwater is widely available under the Antarctic Ice Sheet and chemical constituents within it have the potential to drive geochemical weathering processes in the subglacial environment. Meteoric 10Be is a cosmogenic nuclide with a half-life of 1.39×106 years that is incorporated into glacier ice, therefore its abundance in the subglacial environment in Antarctica is meltwater dependent. It is known to adsorb to fine-grained particles in aqueous solution, precipitate with amorphous oxides, and/or be incorporated into authigenic clay structures during chemical weathering. The presence of 10Be in weathering products derived from beneath the ice therefore indicates chemical weathering processes in the subglacial environment. Freshly emerging subglacial sediments from the Mt. Achernar blue ice moraine were subject to chemical extractions where these weathering phases were isolated and 10Be concentrations therein quantified. Optimization of the phase isolation was developed by examining the effects of each extraction on the sample mineralogy and chemical composition. Experiments on 10Be desorption revealed that pH 3.2-3.5 was optimal for the extraction of adsorbed 10Be. Vigorous disaggregation of the samples before grain size separations and acid extractions is crucial due to the preferential fractionation of the nuclide with clay-sized particles. 10Be concentrations of 2-22×107 atoms g-1 measured in oxides and clay minerals in freshly emerging sediments strongly indicate subglacial chemical weathering in the catchment of the Mt. Achernar moraine. Sediment-meltwater contact in the system was calculated to be on the order of thousands of years, based on total 10Be sample concentrations, local basal melt rates, and 10Be ice concentrations. Strong correlation (R = 0.96) between 10Be and smectite abundance in the sediments indicate authigenic clay formation in the subglacial environment. This study shows that meteoric 10Be is a useful tool to characterize subglacial geochemical weathering processes under the Antarctic Ice Sheet.

No description available.