Publication: Factores que controlan la evolución de los parámetros cristaloquímicos y asociaciones minerales en las rocas sedimentarias del Grupo Enciso (Cretácico Inferior), Cuenca de Cameros, La Rioja (Norte de España)
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Publication Date
1999
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Sociedad Geológica de España
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Abstract
Los materiales del Grupo Enciso pertenecen a la secuencia deposicional 5 (Barremiense superior - Aptiense inferior) de la Cuenca de Cameros. Esta cuenca presenta una potente serie de materiales de origen continental (hasta 9000 m) y el sector E de la misma fue afectado por un metamorfismo de origen hidrotermal. Los sedimentos del Grupo Enciso fueron depositados en sistemas lacustres de tipo rampa de baja energía y bajo gradiente, estando constituidos fundamentalmente por una alternancia de lutitas, margas, calizas y areniscas en proporciones variables. La mineralogía global de los sedimentos pelíticos está constituida por filosilicatos, carbonatos (calcita y dolomita), cuarzo y feldespatos alcalinos. La mineralogía de arcillas está compuesta principalmente por ilita y clorita en todo el rango de condiciones metamórficas estudiadas. Esporádicamente existen también pequeñas cantidades de caolinita, esmectita, pirofilita y diferentes tipos de minerales interestratificados. Existe un descenso de las condiciones metamórficas desde las zonas depocentrales hacia las zonas marginales de la cuenca, aunque no se observa una tendencia clara de evolución en la vertical de los diferentes parámetros cristaloquímicos en función de los cuales se realizan las estimaciones del grado metamórfico
alcanzado, aún siendo series muy potentes. Esto es debido a que los principales factores que condicionan el grado metamórfico de estos sedimentos son la composición global de las muestras y la permeabilidad de los materiales, que controla la circulación de fluidos durante el metamorfismo. Así, los efectos del metamorfismo hidrotermal estarían sobreimpuestos a la diagénesis de enterramiento que sufrieron estos materiales
Sedimentary rocks from Enciso Group belong to the Depositional Sequence 5 (upper Barremian -lowef Aptian) of the Cameros Basin. The basin has a thick sedimentary pile of continental materials (up to 9000 m) and the eastern sector of the Basin was affected by a hydrothermal metamorphic event. These materials were deposited in a low energy and low gradient lacustrine depositional system, and are mainly made up by an alternance of lutites, marlstones, limestones and sandstones. The bulk mineralogy of the pelitic sediments is formed by phyllosilicates, carbonates (calcite and dolomite), quartz and feldspar. The clay mineralogy is mainly formed by illite and chlorite in all the range of studied conditions. Occasionally small amounts of kaolinte, smectite, pyrophyllite and different types of mixed layered minerals are found. A decrease in the metamorphic conditions from the depocentral to the marginal areas of the basin is observed, although for a given profile, no vertical trend in the crystalchemical parameters used to estimate the metamorphic conditions is observed. This is due to factors such as bulk chemical composition and permeability, which limit the fluid flow during metamorphism, and exert an important control in the metamorphism. Therefore, the effect of the hydrothermal metamorphism would be superimposed to the deep burial diagenesis that affected these sediments
Sedimentary rocks from Enciso Group belong to the Depositional Sequence 5 (upper Barremian -lowef Aptian) of the Cameros Basin. The basin has a thick sedimentary pile of continental materials (up to 9000 m) and the eastern sector of the Basin was affected by a hydrothermal metamorphic event. These materials were deposited in a low energy and low gradient lacustrine depositional system, and are mainly made up by an alternance of lutites, marlstones, limestones and sandstones. The bulk mineralogy of the pelitic sediments is formed by phyllosilicates, carbonates (calcite and dolomite), quartz and feldspar. The clay mineralogy is mainly formed by illite and chlorite in all the range of studied conditions. Occasionally small amounts of kaolinte, smectite, pyrophyllite and different types of mixed layered minerals are found. A decrease in the metamorphic conditions from the depocentral to the marginal areas of the basin is observed, although for a given profile, no vertical trend in the crystalchemical parameters used to estimate the metamorphic conditions is observed. This is due to factors such as bulk chemical composition and permeability, which limit the fluid flow during metamorphism, and exert an important control in the metamorphism. Therefore, the effect of the hydrothermal metamorphism would be superimposed to the deep burial diagenesis that affected these sediments