Determinación de la geometría y relaciones de contacto de un paleoseep de metano emergido en la costa de Navidad (33°56’28,09" S - 71°51’11,10" W)
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2021
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es
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Universidad Andrés Bello
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Licencia CC
Licencia CC
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Los sistemas de cold seeps constituyen emisiones de metano y otros gases de hidrocarburos desde el subsuelo marino hacia la columna de agua y a la atmosfera. Existen registro de cold seeps fósiles o “paleoseeps” desde el Devónico al Cuaternario, en márgenes tectónicos pasivos y activos. Estos se encuentran principalmente como cuerpos carbonatados, con variadas morfologías, atravesando secuencias estratigráficas de cuencas silicoclásticas. El objeto de estudio es un paleoseep de metano emergido en la costa de Navidad (PSN), siendo el propósito de esta investigación, detectar evidencias de filtraciones de metano fósiles a través de métodos geofísicos, su distribución, dimensiones, geometría y su extensión en profundidad, para dilucidar las relaciones de contacto del PSN con la Formación Navidad. Para abordar esta problemática se utilizaron métodos magnéticos, sísmicos y radiométricos con la finalidad de identificar los cuerpos, la susceptibilidad magnética, las discontinuidades en sub-superficie, las velocidades de propagación de ondas de los carbonatos y las concentraciones de radionucleidos al PSN, considerando su procedencia para evaluar la potencialidad como método de exploración de estos sistemas en profundidad. Los resultados de este trabajo mostraron que los cuerpos carbonáticos eran discordantes con la estratigrafía. Las anomalías magnéticas negativas se distribuyeron en cuatro zonas y tuvieron valores entre -10 nT y -70 nT. A partir de la anomalía magnética se realizó un modelamiento magnético, el cual indicó que la susceptibilidad magnética era de 0,0021 y se distribuyó como una capa con protuberancias. La tomografía sísmica corroboró la distribución del PSN en sub-superficie, también evidenció una continuidad lateral con una extensión de 120 m que representó un nivel estratigráfico más denso que las demás rocas, con al menos dos protuberancias verticales registradas y una sin registro que se ubicó 30 m al SW y que alcanzó profundidades de entre 5 m y 11 m. Adicionalmente las concentraciones de torio variaron entre 4 ppm y 6 ppm y las de potasio de 1,4% 0,75%, estos valores fueron elevadas respecto a los carbonatos no quimiosintéticos y se relacionaron a procesos tectónicos y de transporte en el fondo marino. Por lo tanto, el PSN es un sistema que se desarrolló con una extensión de al menos 120 m de longitud NE-SW por 50 m de ancho NW-SE y se encuentra sepultado por los depósitos litorales y tiene una expresión discordante con la estratigrafía.
Cold seep systems constitute emissions of methane and other hydrocarbon gases from the seabed to the water column and to the atmosphere. There are records of cold fossil seeps or "paleoseeps" from the Devonian to the Quaternary, in passive and active tectonic margins. These are mainly found as carbonate bodies, with varied morphologies, crossing stratigraphic sequences of silicoclastic basins. The object of study is a methane paleoseep emerged on the Christmas coast (PSN), the purpose of this research being to detect evidence of fossil methane seepage through geophysical methods, its distribution, dimensions, geometry and its depth in subsurface, to elucidate the contact relationships of the PSN with Formation Navidad. To respond this problem, magnetic, seismic and radiometric methods were used in order to identify bodies, magnetic susceptibility, subsurface discontinuities, wave propagation speeds of carbonates and concentrations of radionuclides to the PSN, considering their provenance to evaluate the potential as a method of exploration of these systems in depth. The results of this work showed that the carbonate bodies were discordant with the stratigraphy. The negative magnetic anomalies were distributed in four zones and had values between -10 nT and -70 nT. From the magnetic anomaly, a magnetic mode was performed, which indicates that the magnetic susceptibility was 0.0021 and it was distributed as a layer with bumps. The seismic tomography corroborated the distribution of the PSN on the subsurface, it also showed a lateral continuity with an extension of 120 m that represented a stratigraphic level most dense than the other rocks, with at least two vertical protrusions registered and one without registration that was located 30 m to the SW and reached depths of between 5 m and 11 m. In addition, thorium concentrations varied between 4 ppm and 6 ppm and those of potassium from 1.4% to 0.75%, these values were high with respect to non-chemosynthetic carbonates and were related to tectonic and transport processes on the seabed. Therefore, the PSN is a system that was developed with an extension of at least 120 m in length NE-SW by 50 m in width NW-SE and is buried by littoral deposits and has a discordant expression with the stratigraphy.
Cold seep systems constitute emissions of methane and other hydrocarbon gases from the seabed to the water column and to the atmosphere. There are records of cold fossil seeps or "paleoseeps" from the Devonian to the Quaternary, in passive and active tectonic margins. These are mainly found as carbonate bodies, with varied morphologies, crossing stratigraphic sequences of silicoclastic basins. The object of study is a methane paleoseep emerged on the Christmas coast (PSN), the purpose of this research being to detect evidence of fossil methane seepage through geophysical methods, its distribution, dimensions, geometry and its depth in subsurface, to elucidate the contact relationships of the PSN with Formation Navidad. To respond this problem, magnetic, seismic and radiometric methods were used in order to identify bodies, magnetic susceptibility, subsurface discontinuities, wave propagation speeds of carbonates and concentrations of radionuclides to the PSN, considering their provenance to evaluate the potential as a method of exploration of these systems in depth. The results of this work showed that the carbonate bodies were discordant with the stratigraphy. The negative magnetic anomalies were distributed in four zones and had values between -10 nT and -70 nT. From the magnetic anomaly, a magnetic mode was performed, which indicates that the magnetic susceptibility was 0.0021 and it was distributed as a layer with bumps. The seismic tomography corroborated the distribution of the PSN on the subsurface, it also showed a lateral continuity with an extension of 120 m that represented a stratigraphic level most dense than the other rocks, with at least two vertical protrusions registered and one without registration that was located 30 m to the SW and reached depths of between 5 m and 11 m. In addition, thorium concentrations varied between 4 ppm and 6 ppm and those of potassium from 1.4% to 0.75%, these values were high with respect to non-chemosynthetic carbonates and were related to tectonic and transport processes on the seabed. Therefore, the PSN is a system that was developed with an extension of at least 120 m in length NE-SW by 50 m in width NW-SE and is buried by littoral deposits and has a discordant expression with the stratigraphy.
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Tesis (Geólogo)
Palabras clave
Costas de Chile, Suelos Salinos, Estructuras Sedimentarias, Subsuelos, Metano, Análisis