The northeastern sector of the Madrid Basin shows a substantial succession of miocene materials that
culminate with the so-called «páramo limestones». The purpose of this study is the identification and
characterization of the deposits that compose the Lower and Intermediate Units, aged Aragonian, in the
left bank of the Henares valley. In addition, the boundary of both units has been reviewed. The findings
show that in the margin of the basin, this boundary is defined by an angular discordance between the
Lower and the Intermediate Units, whereas along the valley it is recognized by disconformities represented
by a change in the sequence evolution