Glacis geometry as a geomorphic marker of recent tectonics: The Guadix–Baza basin (South Spain)

Abstract

The Guadix–Baza basin occupies 4000 km 2, and constitutes the largest intramontane basin of the Betic Cordillera (Southern Spain). It has a well preserved geomorphic surface, a glacis, which started to be eroded when the basin conditions changed from endorheic to exorheic. Taking into account its large preserved surface area (more than 1200 km 2) and its pre-deformational geometry, this geomorphic surface is a useful marker of recent deformation. Combining geological and geomorphological data and high resolution DEM, topographic profiles of the glacis have been produced to estimate vertical displacements caused by active compression and extension structures. These structures have produced relative vertical displacements of up to 100 m from the late middle Pleistocene to the present. Assuming an age for the glacis of between 205 and 600 ka, it has been possible to estimate long-term minimum and maximum vertical rates of the activity of normal faults and folds using this geomorphic surface as a marker. Vertical slip rates range from 0.07 to 0.49 mm/year for the main active normal faults and vertical folding rates range from 0.05 to 0.17 mm/year for several active folds. These long-term vertical slip and folding rates are in accordance with other values previously estimated in other sectors of the Betic Cordillera. When present, detailed geomorphic study of recent glacis is an excellent tool for evaluating active tectonics over large regions.