Recent fault-controlled glacis deformation and its role in the fluvial capture of the Guadix-Baza basin (Betic Cordillera, southern Spain)

Abstract

This work is focussed on the geomorphological changes related to the Pleistocene capture of the formerly endorheic Guadix-Baza basin (Betic Cordillera). We explore the possible tectonic controls in the basin opening through a combined geomorphological and structural study. For this, we have selected a study area that includes the connecting zone between the former endorheic basin and the capture channel (Guadiana Menor River). This zone also includes the SE end of the so-called Tíscar Fault Zone (TFZ) that has been active during the Upper Miocene and onwards. We use the glacis surface that marks the end of the endorheic sedimentation (Middle-Upper Pleistocene), as the main reference surface to identify recent deformation structures. Our results indicate that the main channel crossing the Pozo Alcón glacis (Guadalentín River) shows evidence of high levels of fluvial incision and that some anomalies in the stream longitudinal profile could be correlated to the presence of pre-glacis faults linked to the TFZ. Conversely, abrupt changes in the stream orientation seems to be related to post-glacis downthrow faults. We have identified that the dextral strike-slip Tíscar Fault (the northern boundary of the TFZ) propagates towards the SE as far as the Guadalentín River, giving rise to a deformation band with oblique slip that descends the SW block down to 250 m and affects the glacis surface. Additionally, the Pozo Alcón glacis has undergone distributed deformation mainly achieved by N-S to NE-SW downthrow faults and subordinate WNW faults. The roughly E-W extension within the Pozo Alcón glacis can be interpreted as developed in the extensional lobe at the tip of a dextral strike-slip fault (the Tíscar Fault). According to the orientation (WNW-ESE) and location of the Guadiana Menor River (following the southern boundary of the TFZ), and the relief attenuation and tilting produced by the extensional systems in the Pozo Alcón glacis, we interpret that the later stages of TFZ activity probably controlled and favoured the localisation of the basin capture.