Tectonic geomorphology of an active slow-moving, intrabasinal fault: the Galera Fault (Guadix-Baza Basin, central Betic Cordillera, southern Spain)

Abstract

In this work, we prove the usefulness of morphometric analyses, typically applied to basin-border faults, to define the tectonic geomorphology of a slow-moving, intrabasinal structure: the Galera Fault (Guadix-Baza Basin, southern Spain). The Galera Fault is a 30 km-long, oblique-slip fault with major left-lateral and minor vertical slip components. Through geological and structural analyses, we define for the first time the detailed surface geometry of the fault, which is characterized by features typical of left-lateral strike-slip faults. The morphometric analysis indicates that a combination of slow slip rates and the high erodibility of the juxtaposed basin infill deposits favours a rapid landscape response to fault activity that erases many landscape effects related to active tectonics. This masking is more effective on features generated by strike-slip displacement, leaving only subtle evidence, such as local stream deflections and upstream widening of catchments. In contrast, geomorphic effects related to vertical displacement are better preserved, including the control of the geometry of the main rivers and morphological differences in the drainage network between the two fault blocks. On the upthrown fault block, streams are generally shorter and steeper and have greater valley incision, leading to the development of a badland landscape. Moreover, the vertical deformation of a Middle Pleistocene glacis surface (ca. 90 m) demonstrates the important role of this slow-moving intrabasinal fault in the generation of relief in the Betic Cordillera during recent Quaternary time. Although the impact of this fault on relief building is very low in comparison with oblique-slip, basin-border faults in the mountain range, it has a key control on the Quaternary landscape evolution.