Paleosuelos de sepiolita en el neógeno de la cuenca de Madrid
DOI:
https://doi.org/10.3989/egeol.89455-6500Keywords:
sepiolite, paleosoils, silicification, diagenesis, Madrid basinAbstract
The mineralogical composition from sepiolite bearing clays allows us to stablish remarkable variations among this mineral: smectite, illite, detrital grains (quartz and feldspar) and carbonates (calcite and dolomite) according to bed thickness. Sepiolite formation is related to silicification processes which control textural features, crystallinity degree (sharpness) and sepiolite aggregate size as a function of the SiO2/MgO ratio. Silicification is favoured by CaCO3 and an oscillating water table with dissolution-precipitation mechanisms which give rise to hydromorphic paleosoils in the shallower zones. In these paleosoils sepiolite develops mainly on saponite bearing green clays, with glomerulae and laminated textures. In deeper zones, sepiolite appears with massive textures (grid-type) on clays, cementing when there is a high content of terrigenous minerals, both are diagenetic in origin.
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