Publication: La edad de las ilitas en areniscas
pérmicas y triásicas de la Cordillera Ibérica
mediante el método K/Ar: Implicaciones
en la historia diagenética y evolución
de la cuenca
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Publication Date
1996
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Universidad Complutense de Madrid. Departamento de Estratigraf�a
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Abstract
Las areniscas pérmicas y triásicas de un sondeo de casi mil metros, localizado en Sigüenza (SS-44-3), Cordillera Ibérica, con una composición de sublitoarenitas-grauvacas y arcosas-subarcosas, respectivamente, tienen cementos de ilita formados en varias etapas de su historia diagenética, como demuestran su morfología y composición, las reacciones diagenéticas entre estos componentes y otros minerales no arcillosos y la secuencia general de cementacion. Las edades absolutas determinadas por el método K/Ar indican asímismo que las ilitas autigénicas se han formado entre 202,8 ± 44 M.a. y 153,8 ± 3,4 M.a., es decir, entre el Hettangiense-Sinemuriense y el Callovíense-Tithoniense. Estas edades coinciden con el periodo en que la tectónica extensional fue más intensa en el Aulacógeno Ibérico, con el desarrollo de numerosas manifestaciones volcánicas. La elevación de los flujos caloríficos basales y el movimiento convectivo de los fluidos dieron lugar a la neoformación de las ilitas fibrosas. Las temperaturas para su neoformación, deducidas a partir de la reflectividad de la vitrinita, estarían comprendidas entre 134,8 y 159ºC, con profundidades de enterramiento entre 3.800 y 4.500 m. Estos valores implican la existencia de gradientes geotérmicos muy superiores a los que se pueden deducir de la potencia de sedimentos de la cuenca.
A K/Ar study of the fine-grained authigenic illite in the Permian and Triassic sandstones of the Iberian Range from a Sigüenza well 44-3 core (near 1000 m depth) was performed. The composition of the sandstones range from sublitharenites to greywackes in the Permian and from arkoses to subarkoses in the Buntsandstein. These sandstones show pervasive authigenic illite which occurred during at least three episodes of cementation during the burial history. This is indicated by the compositional and morphological characteristics of the illite and also by the general sequence of cementation. K/Ar age determinations indicate that the episode of illitization range between 202.8±4.4 M.a. to 153.8±3.4 M.a. during Hettangian-Sincmurian to the Callovian-Tithonian. These ages coincide with the period of the most intensive extensional tectonics in the basin coeval with volcanic events. Upward flow of hot fluids from the basement and the convective fluids mouvement produced the fibrous illite growth. Constraints placed by vitrinite reflectance deduced temperatures from the associated organic matter which suggest that the diagenetic illite formed at temperatures between 134.8 and 159.5 ºC from 3 800 to 4500 m in depth. These estimates imply geothermal gradients significantly greater than those that could have been deduced from the burial history reconstruction of the Permo-Triassic basin.
A K/Ar study of the fine-grained authigenic illite in the Permian and Triassic sandstones of the Iberian Range from a Sigüenza well 44-3 core (near 1000 m depth) was performed. The composition of the sandstones range from sublitharenites to greywackes in the Permian and from arkoses to subarkoses in the Buntsandstein. These sandstones show pervasive authigenic illite which occurred during at least three episodes of cementation during the burial history. This is indicated by the compositional and morphological characteristics of the illite and also by the general sequence of cementation. K/Ar age determinations indicate that the episode of illitization range between 202.8±4.4 M.a. to 153.8±3.4 M.a. during Hettangian-Sincmurian to the Callovian-Tithonian. These ages coincide with the period of the most intensive extensional tectonics in the basin coeval with volcanic events. Upward flow of hot fluids from the basement and the convective fluids mouvement produced the fibrous illite growth. Constraints placed by vitrinite reflectance deduced temperatures from the associated organic matter which suggest that the diagenetic illite formed at temperatures between 134.8 and 159.5 ºC from 3 800 to 4500 m in depth. These estimates imply geothermal gradients significantly greater than those that could have been deduced from the burial history reconstruction of the Permo-Triassic basin.