Person:
Fernández Barrenechea, José María

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First Name
José María
Last Name
Fernández Barrenechea
URI
https://hdl.handle.net/20.500.14352/75219
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Geológicas
Department
Mineralogía y Petrología
Area
Cristalografía y Mineralogía
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1997 - 19993
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    Natural fluid-deposited graphite: mineralogical characteristics and mechanisms of formation
    (American journal of science, 1998) Luque Del Villar, Francisco Javier; Pasteris, Jill D.; Wopenka, Brigitte; Rodas González, Magdalena; Fernández Barrenechea, José María
    This paper focuses on the similarities and differences between metamorphic graphite (formed in situ from organic matter) and fluid-deposited graphite. We discuss the formation of fluid-deposited graphite in terms of the source of carbon, the characteristics of the C-bearing fluids (the C-O-H system), the mechanisms of carbon mobilization, and the mechanisms of carbon precipitation. New and existing analytical data are compiled on the physical and chemical characteristics of fluid-deposited graphite olitained by the following techniques: optical microscopy, differential ilierrilal analysis, thermogravimetry, X-ray diffraction, Raman spectroscopy, and stable isotope mass spectrometry. Our discussions focus on major, that is, volumetrically significant, worldwide concentrations of graphite
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    Palaeogeographical significance of clay mineral assemblages in the Permian and Triassic sediments of the SE Iberian Ranges, eastern Spain
    (Palaeogeography, palaeoclimatology, palaeoecology, 1997) Alonso Azcárate, Jacinto; Arche, Alfredo; Fernández Barrenechea, José María; López Gómez, José; Luque Del Villar, Francisco Javier; Rodas González, Magdalena
    The evolution of the palaeogeography of the SE Iberian Basin during the Permian and Triassic represents a general evolution from continental to marine environments. It has been recently studied from the sedimentological, stratigraphical, tectonic and palaeontological points of view. In spite of these results, many aspects of this palaeogeography are still a matter of discussion. In this study, clay mineralogy analysis complements previous studies representing a new aspect for understanding the evolution of the sedimentary environment and the palaeogeography of the Iberian Basin during the periods in question and thus of the palaeogeography and the location of the major high areas in the westernmost border of the Tethys sea. In spite of late diagenetic transformations the original clay mineral associations of the Permian-Triassic sediments of the SE Iberian Ranges can be reconstructed. Seventy-seven samples of siliciclastic and carbonate sediments of these ages have been studied (SEM and XRD), revealing six new aspects that help to precise the palaeogeographical interpretation of the area: (1) Two major mineral assemblages have been found: illite+ kaolinite +pyrophyllite in the continental facies and illite + chlorite + vermiculite + mixed-layer clays in the marine facies. (2) The Mg-rich clay minerals are here considered to be of marine origin. (3) Active phases of basin boundary faults are marked in the sediments by the presence of pyrophyllite, derived directly from the Palaeozoic metamorphic basement. (4) Unconformities separating major depositional sequences also separate formations with different clay mineralogy. (5) Different groups of clay minerals can be separated clearly coinciding with the different palaeogeographical stages also distinguished in the westernmost border of the Tethys sea. (6) The clay mineral associations back up the data of a previous hypothesis of a humid climate for the end of the Permian in the study area just prior to the first incursion of the Tethys sea.
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    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)
    (Revista de la Sociedad Geológica de España, 1999) Alonso Azcárate, Jacinto; Rodas González, Magdalena; Fernández Barrenechea, José María; Mas Mayoral, José Ramón
    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