Facies tsunamigénica en el límite marino transicional de la Fm Horcón, evidencia de paleoterremoto inducido por la subducción del JFR a los 33°S, Valparaíso, Chile
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Fecha
2022
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Facultad/escuela
Idioma
es
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Universidad Andrés Bello
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Licencia CC
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Las secuencias mio-pliocenas pertenecientes a la Formación Horcón, mantienen diversas interpretaciones en cuanto al proceso y dinámica que originó sus contrastantes condiciones de depositación marino-transicionales y progresiva somerización de las secuencias, A esta formación se atribuyen variaciones climáticas y eventos de erosión y alzamiento de la cordillera, sin embargo poco se considera respecto al impacto de la progresiva subducción de la dorsal de Juan Fernández (JFR) en la geometría de las cuencas, así como en el control estructural, evolución de las secuencias y el brusco cambio de ambiente marino a transicional entre los miembros inferior y superior. En el presente estudio, se delimitan y definen por primera vez, los depósitos de tsunamitas y sismitas identificados a lo largo del borde costero comprendido entre caleta Horcón y Maitencillo. Estos depósitos fueron caracterizados a través de columnas estratigráficas, definición de litofacies, asociaciones de facies y obtención de datos estructurales de la costa y del margen continental para su posterior análisis. La integración de los antecedentes permitió inferir que el depósito tsunamigénico marca el abrupto cambio de ambiente deposicional de las secuencias que limitan el miembro inferior y superior de la columna, representando facies asociadas a un evento de gran energía, como un paleoterremoto tsunamigénico, evidenciado en las facies de tsunamitas y sismitas.
La facies de sismitas se localizan en la base de la secuencia (miembro inferior), caracterizada por una superficie de deslizamiento definida por una brecha intraformacional, sobre la cual se identifican estructuras de slumps con vergencia al norte. Esta superficie se asocia a una falla normal NS/40°W, limitada o sellada por el depósito de tsunamita. Las facies de tsunamita, se caracterizan de base a techo por, una capa de conglomerados y brechas tamaño bloques, sobreyacida por areniscas conglomerádicas con variada proporción de Turritellas (10% a 80%). Además, las direcciones principales de fallas tipo normales de la zona sumergida y emergida presentarían similitudes al tener rumbos NE-SW, NS y NW, lo que indicaría que la subducción del JFR habría sido la responsable de generar el paleoterremoto ya que generaría espacios de acomodación, erosión por subducción, alzamiento tectónico, fallas normales que eventualmente generarían terremotos tsunamigénicos.
The Mio-Pliocene sequences belonging to the Horcón Formation, maintain diverse interpretations regarding the process and dynamics that originated its contrasting conditions of marine-transitional deposition and progressive shallowing of the sequences. Climatic variations and erosion and uplift events are conditioned to this formation. of the mountain range, however, little is considered regarding the impact of the progressive subduction of the Juan Fernández Ridge (JFR) on the geometry of the basins, as well as on the structural control, evolution of the sequences and the abrupt change in the marine environment a transitional between the lower and upper limbs. In the present study, the tsunami and seismic deposits identified along the integrated coastline between Caleta Horcón and Maitencillo are delimited and defined for the first time. These deposits were characterized through stratigraphic columns, definition of lithofacies, facies associations and obtaining structural data from the coast and the continental margin for further analysis. The integration of the antecedents allowed us to infer that the tsunamigenic deposit marks the abrupt change in the depositional environment of the sequences that limit the lower and upper members of the column, representing facies associated with a high-energy event, such as a tsunamigenic paleoearthquake, evidenced in the tsunami and earthquake facies. The seismic facies are located at the base of the sequence (lower member), characterized by a slip surface defined by an intraformational breccia, on which north-verging slump structures are identified. This surface is associated with a NS/40°W normal fault, limited or sealed by the tsunami deposit. Tsunamita facies are characterized from base to top by a layer of conglomerates and size block breccias, overlain by conglomerate sandstones with a varying proportion of Turritellas (10% to 80%). In addition, the main directions of normal type faults in the submerged and emerged zone would present similarities as they have NE-SW, NS and NW courses, which would indicate that the subduction of the JFR would have been responsible for generating the paleoearthquake since it would generate accommodation spaces., subduction erosion, tectonic uplift, normal faulting that would eventually generate tsunamigenic earthquakes.
The Mio-Pliocene sequences belonging to the Horcón Formation, maintain diverse interpretations regarding the process and dynamics that originated its contrasting conditions of marine-transitional deposition and progressive shallowing of the sequences. Climatic variations and erosion and uplift events are conditioned to this formation. of the mountain range, however, little is considered regarding the impact of the progressive subduction of the Juan Fernández Ridge (JFR) on the geometry of the basins, as well as on the structural control, evolution of the sequences and the abrupt change in the marine environment a transitional between the lower and upper limbs. In the present study, the tsunami and seismic deposits identified along the integrated coastline between Caleta Horcón and Maitencillo are delimited and defined for the first time. These deposits were characterized through stratigraphic columns, definition of lithofacies, facies associations and obtaining structural data from the coast and the continental margin for further analysis. The integration of the antecedents allowed us to infer that the tsunamigenic deposit marks the abrupt change in the depositional environment of the sequences that limit the lower and upper members of the column, representing facies associated with a high-energy event, such as a tsunamigenic paleoearthquake, evidenced in the tsunami and earthquake facies. The seismic facies are located at the base of the sequence (lower member), characterized by a slip surface defined by an intraformational breccia, on which north-verging slump structures are identified. This surface is associated with a NS/40°W normal fault, limited or sealed by the tsunami deposit. Tsunamita facies are characterized from base to top by a layer of conglomerates and size block breccias, overlain by conglomerate sandstones with a varying proportion of Turritellas (10% to 80%). In addition, the main directions of normal type faults in the submerged and emerged zone would present similarities as they have NE-SW, NS and NW courses, which would indicate that the subduction of the JFR would have been responsible for generating the paleoearthquake since it would generate accommodation spaces., subduction erosion, tectonic uplift, normal faulting that would eventually generate tsunamigenic earthquakes.
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Tesis (Geólogo)
Palabras clave
Zonas de Subducción, Sedimentos Marinos, Variaciones climáticas, Chile, Chile, Valparaíso