El límite Unidad Inferior-Unidad Intermedia de la Cuenca de Madrid en el valle del Henares (Provincia de Guadalajara)

Abstract

The aim of this study is reviewing the stratigraphy of the Neogene alluvial deposits in the north border of the Madrid Basin with relation to the activity of the south border of the Central System, specifically in the left bank of the Henares river (Guadalajara province). A detailed cartography and a stratigraphic analysis of the sediments that constitute the Lower and Intermediate Units were carried out. In addition, four stratigraphic series and two synthetic sections were completed in order to establish a correlation of the limit between them and to delimit both units alongside the left bank of the Henares river in a north-south direction. The results indicate that in the southern areas, this limit is represented by a change in the evolution of the sequences, which is defined by a conglomeratic level over a paleosoil or clay deposits. However, in the northern areas, the limit has been recognized by an angular discordance between the Intermediate Unit (practically horizontal) and the Lower Unit (dipping 15º to the south). This onlap would represent a slow down in the tectonic activity. These findings, contrary to previous works, indicate that the initiation of the Intermediate Unit deposition is not caused by tectonic reactivation.