Sedimentología y petrología de los abanicos aluviales y facies adyacentes en el Neogeno de Paracuellos de Jarama (Madrid)

Abstract

Lateral and vertical variations of middle Miocene lithofacies (Lower and Intermediate Units of the Miocene of the Madrid Basin) have been analyzed in the Paracuellos de Jarama area, near Madrid. A complete transition from medial to distal alluvial fan facies and palustrinelshaltow 1acustrine deposits can be observed. This sedimentary evolution is inferred from the detailed sedimentological. analysis carried out in each of the previously defined lithostratigraphic units: a₁) Green shale and dolomite Unit, a₂) Brown clays, arkosic and carbonate Unit; these two units are linked together into a Lower Group. b) Coarse Arkosic Unit (Upper Group). Facies relationsbips within the Lower Group show a lateral change pattern between alluvial fan deposits, and palustrine deposits. Also the former ones gradually prograde over the palustrine deposits, as deduced from vertical evolution in the southernmost parts of the area. Upper Group represents a sudden progradation of the alluvial fan systems, that extensively overlie the distal facies observed in the Lower Group.
Wide development of calcretes, sepiolite deposits, and nodular chert is an outstanding feature in the most distal parts of the alluvial fan bodies. They are studied in some detail provided the scarcity of well described examples of facies relationships in the kinds of deposits.