Geomorfología del sector meridional de la cuenca del Guadiana

Abstract

A geological and geomorphological study in the southern sector of the Guadiana Basin has allowed us to establish an approach to the sequence of morphogenetic events and stratigraphic record during the Tertiary and Quaternary eras. The planation surface generated in pre-Tertiary times was block faulted by a tectonic activity that gave rise to a smooth basin in this part of the Hercynian Massif. At once the soil and weathering pro files located at topside of landforms were eroded and the resulting products laid down the basin. Two detrital formations have been distinguished in the Oligo-Miocene deposits. At the lower part, lacustrine clays (Lobon formation) with very variable thickness (less than 80 m) lay on weathered and smoothed basement. After that, fluvial sands and gravels (Almendralejo and Badajoz facies) are deposited with a expansive way, together with a tectonic deformation with N120ºE and N40ºE fault trends. Upper Miocene sedimentation is represented by a thin limestone (2 m), like calcrete facies, deposited on swamps with periodic oscillations of the water level and semiarid climatic conditions. The top plain of the Neo gene succession connects with a pediment on outcropping basement. During Pliocene both surfaces were tilted to the NW and Plio-Quaternary deposits (Raña) were produced.