Proveniencia y dinámica de aguas e implicancias paleoambientales de carbonatos del sistema kárstico del seno Barros Luco, Isla Madre de Dios, Patagonia, Chile
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2018
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es
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Universidad Andrés Bello
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En este trabajo se presentan los primeros antecedentes hidrogeológicos del sistema kárstico que alberga la isla Madre de Dios, junto con nuevos datos isotópicos de las rocas que forman parte de la unidad Calizas Tarlton (CT), en la Patagonia chilena. Se determina la dinámica de las aguas del sistema kárstico del Seno Barros Luco y se establece la interacción existente entre éstas con las rocas carbonatadas de la unidad Caliza Tarlton, a partir de la cual se identifica su potencial en la interpretación de paleo-ambientes. El estudio se enmarca en la Expedición Última Patagonia 2017, desarrollada por la asociación francesa Centre Terre en el sector comprendido entre el canal Trinidad y el seno Barros Luco en la isla Madre de Dios.
Las texturas deposicionales, en su mayoría reconocidas como mudstone, y la ausencia de evidencias de recristalización y/o deformación, así como los rangos de composición isotópica de δ13C de las rocas constituyentes de las CT, que incrementan con la altura en la columna, evidencian la existencia de una transgresión marina durante su formación (Pensilvaniano medio-Pérmico temprano), en un ambiente deposicional marino (3.7‰ δ13CVPDB promedio) de aguas tranquilas, probablemente asociado a una plataforma carbonatada similar a un arrecife.
Las composiciones isotópicas de δ18O y δ2H de las muestras de agua junto con las mediciones de salinidad de estas (mediante la conductividad eléctrica) revelan un significativo control de las aguas meteóricas, existiendo una rápida recarga del sistema, el cual en su evolución incorpora humedad externa, reflejado en un incremento de los valores de exceso de deuterio, y una mayor interacción agua-roca en profundidad, evidenciado en el aumento de valores de conductividad eléctrica. Las aguas meteóricas caídas en el período medido, entre el 4 y 24 de febrero, entrega una primera aproximación a la Línea de Aguas Meteóricas Local de la isla Madre de Dios dada por la relación δ2H = 7,58 * δ18O + 3,37 (R² = 0,95; N=16), cuyas masas de aire transportadoras de la humedad provienen principalmente desde el SO (60°S). Se aprecia el efecto altitudinal en las aguas de la isla, lo que determina la existencia de dos marcados grupos caracterizados por composiciones isotópicas más o menos empobrecidas, para las muestras colectadas a mayor o menor altura, respectivamente.
De esta manera, queda demostrado el potencial como indicador paleo-ambiental de las rocas carbonatadas de la unidad Calizas Tarlton. Sin embargo, un trabajo más amplio es necesario para una interpretación íntegra acerca de las condiciones de formación de la unidad, así como de la dinámica del sistema kárstico comparando y modelando la interacción de las aguas con el carbonato, complementando el análisis con otros trazadores.
In this work the first hydrogeological antecedents of the karstic system that shelters the Madre de Dios Island are presented, together with new isotopical data from the rocks parts of the Calizas Tarlton (CT) unit, in the Chilean Patagonia. The dynamics and interaction of the karst system waters of Seno Barros Luco were determined and the existing interaction between them with the carbonate rock of the CT is established, from which its potential in the interpretation of paleo-enviroments is identified. The study is part of the expedition Ultima Patagonia 2017, developed by the french association Centre Terre in the sector comprised by the Trinidad channel and the Barros Luco fjord on the Madre de Dios Island. The depositional textures, mostly identified as mudstones, and the absence of evidence of recrystallization and/or deformation, as well as the δ 13C values of the rocks part of the CT, that increase through the column, show the existence of a marine transgression during its formation (middle Pennsylvanian-early Permian), in a marine depositional enviroment (mean 3.7‰ δ 13CVPDB) of calm waters, probably associated to a carbonate platform similar to a reef. The δ 18O and δ2H isotopic compositions of the water samples together with its salinity measurements (by the electrical conductivity) reveal a significant control of the meteoric waters, there being a rapid recharge of the system, which in its evolution incorporates external moisture reflected in an increase in deuterium excess values, and a greater water-rock interaction in depth, evidenced in the increase of the electrical conductivity values. The meteoric waters dropped in the measured period, between February 4th and 24th , gives a first approximation to the Local Meteoric Water Line of the Madre de Dios Island given by the equation: δ 2H = 7,58 * δ18O + 3,37 (R² = 0,95; N=16), whose aire masses transport moisture mainly come from the SW (60°S). It is verified the altitudinal effect in the waters of the Island, which determines the existence of two marked groups characterized by more or less enriched isotopic composition, respectively. Consequently, the potential as a paleo-enviroment indicator of the carbonate rocks of the CT unit its demostrated. However a broader work is necessary for a full interpretation of the formation conditions of the unit, as well as the dynamics of the karst system comparing and modeling the interaction of water with carbonate, complementing the anlysis with others tracers.
In this work the first hydrogeological antecedents of the karstic system that shelters the Madre de Dios Island are presented, together with new isotopical data from the rocks parts of the Calizas Tarlton (CT) unit, in the Chilean Patagonia. The dynamics and interaction of the karst system waters of Seno Barros Luco were determined and the existing interaction between them with the carbonate rock of the CT is established, from which its potential in the interpretation of paleo-enviroments is identified. The study is part of the expedition Ultima Patagonia 2017, developed by the french association Centre Terre in the sector comprised by the Trinidad channel and the Barros Luco fjord on the Madre de Dios Island. The depositional textures, mostly identified as mudstones, and the absence of evidence of recrystallization and/or deformation, as well as the δ 13C values of the rocks part of the CT, that increase through the column, show the existence of a marine transgression during its formation (middle Pennsylvanian-early Permian), in a marine depositional enviroment (mean 3.7‰ δ 13CVPDB) of calm waters, probably associated to a carbonate platform similar to a reef. The δ 18O and δ2H isotopic compositions of the water samples together with its salinity measurements (by the electrical conductivity) reveal a significant control of the meteoric waters, there being a rapid recharge of the system, which in its evolution incorporates external moisture reflected in an increase in deuterium excess values, and a greater water-rock interaction in depth, evidenced in the increase of the electrical conductivity values. The meteoric waters dropped in the measured period, between February 4th and 24th , gives a first approximation to the Local Meteoric Water Line of the Madre de Dios Island given by the equation: δ 2H = 7,58 * δ18O + 3,37 (R² = 0,95; N=16), whose aire masses transport moisture mainly come from the SW (60°S). It is verified the altitudinal effect in the waters of the Island, which determines the existence of two marked groups characterized by more or less enriched isotopic composition, respectively. Consequently, the potential as a paleo-enviroment indicator of the carbonate rocks of the CT unit its demostrated. However a broader work is necessary for a full interpretation of the formation conditions of the unit, as well as the dynamics of the karst system comparing and modeling the interaction of water with carbonate, complementing the anlysis with others tracers.
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Tesis (Geólogo)
Palabras clave
Rocas, Hidrogeología, Geología Ambiental, Patagonia, Exploraciones y Descubrimientos, Chile, Región de Aysén, Chile