Sedimentología de las facies detríticas de la Unidad Intermedia del Mioceno al sur y este de Madrid

Abstract

Micaceous sandstone beds form a characteristic lithofacies of the Middle Miocene deposits in the north-eastern side of the Madrid Basin. They are arranged in a transitional position between arkosic marginal deposits and central lutite-carbonate sediments in the basin.
Biotite mica grains account for more than half of the total number grains in most of the sandstone beds, Also, mica grains commonly reach up 20-30 percent of the sample weight. Micaceous sandstones occur in two different depositional systems. They were deposited as sheet floods and moderately sinuous streams in the Alcalá-Torrejón area (medial to distal sequences of an alluvial-playa complex coming from the NE). Near Madrid and to the south of the city (Pinto-Esquivias area), micaceous sandstones occur as channel fills, sheet-flood deposits and small deltaic sequences, They were derived from arkosic alluvial fans.
Some considerations about the peculiarities of the micaceous sandstones have been made in order to envisage corrections on grain-size distributions. Presumed corrections are derived from high mica contents and flattened shapes of these grains.