%0 Journal Article
%A Fesharaki, Omid
%A García Romero, Emilia
%A Cuevas González, Jaime
%A López Martínez, María Nieves
%T Clay mineral genesis and chemicalevolution in the Miocene sediments ofSomosaguas, Madrid Basin, Spain
%D 2007
%@ 0009-8558
%U https://hdl.handle.net/20.500.14352/50682
%X A mineralogical and microtextural study of Somosaguas Miocene deposits, locatedin the Madrid Basin (western Madrid, Spain), was carried out using X-ray diffraction, scanningelectron microscopy, transmission electron microscopy and optical microscopy, whereas crystalchemistry data were obtained by analytical electron microscopy-transmission electron microscopyand electron icroprobe analysis. Four stratigraphic sections were studied, compising detrital rocksrepresenting intermediate and distal facies from alluvial fan deposits. The predominant source area ofthese sediments was the granitic rocks of the Spanish Central System with a lesser contribution ofmetamorphic rocks. Clayey arkoses are the most abundant rocks of these sections, typical of granitealteration under warm, semi-arid climates. The mineralogy is characterized by phyllosilicates,followed by feldspars and quartz. The data obtained reveal mineral mixtures of detrital (quartz,feldspars, kaolinite, micas and chlorite), transformed (illite and beidellite) and neoformed(montmorillonite) origin. Clay minerals resulted from interactions between detrital minerals andmeteoric waters. Two trends of degradation of micas are detected. The first shows a transition frommuscovites and dioctahedral illites, to beidellites. The other trend is defined by the biotitedegradation to beidellites with different layer charge and octahedral Fe content. Montmorilloniteswere neoformed from the hydrolysis and weathering of primary minerals (feldspars and muscovite).Magnesian clay minerals such as sepiolite, palygorskite and trioctahedral smectites, extremelyabundant in the centre of the basin, were not detected in Somosaguas sediments.
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