Litoestratigrafía y evolución paleogeográfica del Mioceno del borde NE de la Cuenca de Madrid (Prov. Guadalajara)

Abstract

Miocene deposits of the NE area of the Madrid Basin are studied in this paper. Difierent stratigraphic units are defined and a model of paleogeographic evolution of the NE area of the Madrid Basin is proposed. The three Units previously defined in the Neogene deposits of the Madrid Basin are recognized in this area. These Units, which are bounded by sedimentary discontinuities, have been called: Lower, Intermediate and Upper Miocene Units. Age of these units can be assesed to upper Agenian to middle Aragonian for the Lower Unit; middle Aragonian to 10wer Vallesian for the Intermediate one and lower Aragonian to Turolian for the Upper Unit. Vertical succesions into each of the Units are formed by one single fining-thinning sequence in the Lower and Upper Units and by two fining-thinning sequences in the Intermediate one. Each of the sequences show the progressive retreat of the alluvial systems and later developmet of shallow lacustrine environments. Sedimentation of Lower and Intermediate Units took place in a elosed basin in which tectonic activity events in the margins of the basin resulted in the progradation of the alluvial fan systems and in the retreat of the shallow lacustrine environments. Two different progradation events have been detected. The first corresponds to the bottom of the Intermediate Unit and the other corresponds to the middle part of this Unit. Both events can be recognized in the marginal deposits (sudden increase in grain size) as well as in the more distal ones (detrital deposits are overlying carbonate facies). Location of the different alluvial fan systems is controlled by the paleomorphology and structurallineations of the margin of the basin (Central System and Iberian Range). These alluvial fan systems evolved laterally to wide f100d plains in which shallow lacustrine environments were developed. These lacustrine environments had their greater development in the top of the Intermediate Unit.