The Ethiopian Plateau is one of the few tectonically-active regions on Earth that is situated in continental rift zones. About 1.6 km deep gorge of the Nile was carved by the Blue Nile River on the Ethiopian Plateau, as the plateau has been experiencing continuous uplift and exhumation in the Cenozoic. Here, we used quantitative analysis of longitudinal rive-profile forms and parameters (knickpoint and normalized steepness-index ksn) of the Blue Nile tributaries to tease out regional tectonic signals. 244 knickpoints were examined in the tributaries, majority (>80%) of which are unassociated with lithology or geological structures. Knickpoint distribution throughout the plateau reveals three incision phases. The novel approach of correlation of ksn with mantle tomography suggests that higher and lower ksn values occur above low-velocity and high-velocity zones, respectively, indicating that thermal upwelling beneath the plateau linked to Afar mantle plume largely controls the uplift thus incision of the plateau.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18083号 / 理博第3961号 / 新制||理||1571(附属図書館) / 30941 / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 千木良 雅弘, 教授 釜井 俊孝, 准教授 松四 雄騎 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

The lower Da-An River in western Taiwan was uplifted ~10 during the 1999 Mw 7.6 Chi-Chi earthquake, resulting in a 20- to 30-m-deep bedrock gorge. However, the amount of coseismic displacement along the channel bed does not fully explain the resulting bedrock channel incision. Using a series of aerial photographs, digital terrain models (DEM), and real-time kinematic global positioning system (RTK GPS) surveys, we characterized knickpoint retreat and fluvial incision in the Da-An River gorge. We also analyzed discharge and precipitation data and collected measurements of rock strength and joint plane orientations to understand the climatic, lithological, and structural influence on the evolution of the actively incising gorge. Two stages of fluvial incision and knickpoint migration are identified in the gorge following surface uplift during the Chi-Chi earthquake. From 1999 to 2004, 3 to 5 m of alluvium was removed from the channel bed, followed by 3 to 4 m of bedrock channel incision. The knickpoint generated immediately after the earthquake stayed where the uplift occurred at this time. Since 2005, the channel bed has lowered rapidly with local incision rate as high as 15 m/yr in terms of knickpoint migration. The average knickpoint migration rate over the period 2005 to 2009 was 238 m/yr; total upstream migration from the location of knickpoint formation was 1190 m. While tectonic uplift formed the knickpoint and set the stage for channel incision, climate played a critical role in accelerating the fluvial response to coseismic displacement. More than 20 m of bedrock channel incision and 1180 m knickpoint migration occurred during the post-2004 typhoon seasons (May-October). Based on repeat surveys of the Da-An River longitudinal profile and analysis of precipitation and discharge data, we suggest that a discharge threshold of 1200 to 2600 m³/s is required to initiate upstream knickpoint migration. However, once the threshold is exceeded, bedding dip becomes the primary control on rates and patterns of knickpoint propagation. Rotation occurred in a hinge zone where the bedding dips change from horizontal to upstream-dipping, while replacement was observed in the strata dipping upstream. The highest knickpoint migration rates (> 300 m/yr) were recorded in flat-lying, horizontal strata (< 10º) where parallel retreat was the dominate process. Overall, the knickpoint propagation followed the process of replacement behavior, in which the height of knickpoint decreases while migrating upstream. Thus, while tectonic processes set the initial conditions for knickpoint propagation in the Da-An River, the response time of the fluvial system to this forcing is strongly dependent on climate and local structure.

Fundação Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro / O Rio do Paraíba do Sul está encaixado sobre rochas neoproterozóicas do Brasiliano possuindo uma direção principal ENE-WSW que companha o strike das camadas geológicas. Próximo à cidade de Sapucaia-RJ o vale deste rio apresenta um estrangulamento denominado aqui de Estreito de Sapucaia. Através da análise de mapa hipsométrico, de perfis topográficos e do perfil longitudinal do Rio Paraíba do Sul, foi constatado que a feição morfológica do Estreito de Sapucaia é um divisor de drenagem regional de direção NNW-SSE e um nível de base regional que dita o trabalho erosivo realizado pelo Paraíba do Sul e de parte de seus afluentes na área estudada. O mapa hidrológico apresenta canais com mudanças abruptas de direção, indicativos de capturas de drenagem, sendo que muitas vezes essa mesma direção continua nos canais de bacias hidrográficas contíguas formando lineamentos de vales separados por um divisor. Estas capturas de drenagem acontecem em afluentes do Rio Paraíba do Sul que possuem direções contrárias a ele, assim como o Rio Calçado que flui por cerca de 20 km na direção oposta até mudar de direção próximo a sua foz no próprio Rio Paraíba do Sul. Estes canais de direção contrária ao rio principal sugerem a existência de uma antiga direção principal para oeste, que foi modificada por capturas de drenagem originadas a partir do rebaixamento de um paleo-divisor que existia no local onde hoje é o Estreito de Sapucaia e que dividia o Paraíba do Sul em dois segmentos de direções distintas, ENE e WSW. Acredita-se que este fato ocorreu durante a reativação tectônica rúptil na transição Mesozóico/Cenozóico quando foram geradas estruturas que se sobrepuseram às antigas estruturas até então existentes, reorganizando, assim, a distribuição dos fluxos hidrológicos. A inversão da direção do fluxo hidrológico para ENE aumentou a área de influência do Paraíba do Sul incrementando a quantidade de sedimentos disponíveis para o preenchimento da Bacia de Campos. Desta forma, acredita-se que esta captura de drenagem teve como data o Meso-Eoceno que marca o momento em que a Bacia de Campos deixa de estar faminta para receber um grande aporte sedimentar / The Paraíba do Sul River flows over.Neoproterozoic rocks of Brasiliano, with preference direction ENE-WSW the same of the strike of geologic layers. In the Sapucaia-RJ city the valley of Paraíba do Sul river is strangle. This feature is called here Sapucaia Strait. Throught the analysis of the Hipsometric Map, the topographies profiles and the longitudinal profile of the Paraíba do Sul River, was verified that this morphological feature is a regional drainage divided with NNW-SSE direction and a regional Knickpoint thats commands the erosion realized by the Paraíba do Sul River and his tributaries. The Hidrologic Map shows streams with abrupt changing of direction. Sometimes this direction continuous in streams of hidrological basins contiguous, originating relief lineaments, indicating stream capture. These stream captures happen in the tributaries of the Paraíba do Sul River with different direction of him, like the Calçado River that flows 20 km in the opposite direction up to his outfall in the property Paraíba do Sul River. These channels with opposite direction of the leading river suggest the existence of archaic mainly direction to West, thats being modified by the streams captures originated by the degrade of one paleo-divider that exists in the place where today is the Sapucaia Strait and divided the Paraíba do Sul River in two segments, ENE e WSW. This research, believes that this fact occurred at the Mesozoic/Cenozoic tectonic when was created structures that overlapped the olds structures that exists, reorganizing the distribution of the hydrologic flows. The inversion of the hydrologic flows increased the area of the Paraíba do Sul River enlarging the quantity of sediments that fills the Campos Basin. We expect, that this stream capture occurred in Meso-Eoceno when the Campos Basin stop to be starving and passes to receive a lot of sediments

Fundação Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro / O Rio do Paraíba do Sul está encaixado sobre rochas neoproterozóicas do Brasiliano possuindo uma direção principal ENE-WSW que companha o strike das camadas geológicas. Próximo à cidade de Sapucaia-RJ o vale deste rio apresenta um estrangulamento denominado aqui de Estreito de Sapucaia. Através da análise de mapa hipsométrico, de perfis topográficos e do perfil longitudinal do Rio Paraíba do Sul, foi constatado que a feição morfológica do Estreito de Sapucaia é um divisor de drenagem regional de direção NNW-SSE e um nível de base regional que dita o trabalho erosivo realizado pelo Paraíba do Sul e de parte de seus afluentes na área estudada. O mapa hidrológico apresenta canais com mudanças abruptas de direção, indicativos de capturas de drenagem, sendo que muitas vezes essa mesma direção continua nos canais de bacias hidrográficas contíguas formando lineamentos de vales separados por um divisor. Estas capturas de drenagem acontecem em afluentes do Rio Paraíba do Sul que possuem direções contrárias a ele, assim como o Rio Calçado que flui por cerca de 20 km na direção oposta até mudar de direção próximo a sua foz no próprio Rio Paraíba do Sul. Estes canais de direção contrária ao rio principal sugerem a existência de uma antiga direção principal para oeste, que foi modificada por capturas de drenagem originadas a partir do rebaixamento de um paleo-divisor que existia no local onde hoje é o Estreito de Sapucaia e que dividia o Paraíba do Sul em dois segmentos de direções distintas, ENE e WSW. Acredita-se que este fato ocorreu durante a reativação tectônica rúptil na transição Mesozóico/Cenozóico quando foram geradas estruturas que se sobrepuseram às antigas estruturas até então existentes, reorganizando, assim, a distribuição dos fluxos hidrológicos. A inversão da direção do fluxo hidrológico para ENE aumentou a área de influência do Paraíba do Sul incrementando a quantidade de sedimentos disponíveis para o preenchimento da Bacia de Campos. Desta forma, acredita-se que esta captura de drenagem teve como data o Meso-Eoceno que marca o momento em que a Bacia de Campos deixa de estar faminta para receber um grande aporte sedimentar / The Paraíba do Sul River flows over.Neoproterozoic rocks of Brasiliano, with preference direction ENE-WSW the same of the strike of geologic layers. In the Sapucaia-RJ city the valley of Paraíba do Sul river is strangle. This feature is called here Sapucaia Strait. Throught the analysis of the Hipsometric Map, the topographies profiles and the longitudinal profile of the Paraíba do Sul River, was verified that this morphological feature is a regional drainage divided with NNW-SSE direction and a regional Knickpoint thats commands the erosion realized by the Paraíba do Sul River and his tributaries. The Hidrologic Map shows streams with abrupt changing of direction. Sometimes this direction continuous in streams of hidrological basins contiguous, originating relief lineaments, indicating stream capture. These stream captures happen in the tributaries of the Paraíba do Sul River with different direction of him, like the Calçado River that flows 20 km in the opposite direction up to his outfall in the property Paraíba do Sul River. These channels with opposite direction of the leading river suggest the existence of archaic mainly direction to West, thats being modified by the streams captures originated by the degrade of one paleo-divider that exists in the place where today is the Sapucaia Strait and divided the Paraíba do Sul River in two segments, ENE e WSW. This research, believes that this fact occurred at the Mesozoic/Cenozoic tectonic when was created structures that overlapped the olds structures that exists, reorganizing the distribution of the hydrologic flows. The inversion of the hydrologic flows increased the area of the Paraíba do Sul River enlarging the quantity of sediments that fills the Campos Basin. We expect, that this stream capture occurred in Meso-Eoceno when the Campos Basin stop to be starving and passes to receive a lot of sediments

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第21577号 / 理博第4484号 / 新制||理||1644(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)教授 千木良 雅弘, 教授 釜井 俊孝, 准教授 松四 雄騎 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Deep-marine sandstones containing significant (> 10%) detrital mud (silt and clay) matrix have become increasingly recognized, but mostly in drill core or poorly exposed outcrops where details of their vertical and lateral variability are poorly captured. Exceptional vertical and along-strike exposures of matrix-rich and associated matrix-poor deposits in deep-marine strata of the passive margin Neoproterozoic Windermere Supergroup and foreland basin Ordovician Cloridorme Formation, provide an unparalleled opportunity to document such characteristics. In both study areas, strata form a 100s m long depositional continuum that at its upflow end consists of thick-bedded matrix-poor sandstone (<20% matrix) that transforms progressively downflow to medium- to thick-bedded muddy sandstone (20 – 50% matrix) to medium-bedded bipartite facies with a basal sandy (30 – 60% matrix) part overlain sharply by a muddier part (40 – 80% matrix), and then to thin-bedded sandy mudstone (50 – 90% matrix). This depositional continuum is then overlain everywhere by a thin- to very thin-bedded traction-structured sandstone and/or silty mudstone cap. This consistent lithofacies change is interpreted to reflect particle settling in a rapidly but systematically evolving, negligibly-sheared sand-mud suspension developed along the margins (Windermere) and downflow terminus (Cloridorme) of a high-energy, mud-enriched avulsion jet. Stratigraphically upward, beds of similar lithofacies type succeed one another vertically and transform to the next facies in the depositional continuum at about the same along-strike position, forming stratal units 2–9 beds thick whose grain-size distribution gradually decreases upward. This spatial and temporal regularity is interpreted to be caused by multiple surges of a single, progressively waning turbidity current, with sufficient lag between successive surges for the deposition of a traction-structured sandstone overlain by mudstone cap. Furthermore, the systematic backstepping or side-stepping recognized at the stratal unit scale in both the Windermere and Cloridorme is interpreted to be driven by a combination of knickpoint migration and local topographic steering of the flows, which continued until the supply of mud from local seafloor erosion became exhausted, the main channel avulsed elsewhere, or a new stratal element developed.