The summit erosion surfaces of the inner Betic Cordillera: Their value as tools for reconstructing the chronology of topographic growth in southern Spain
Résumé
Erosion surfaces at the top of mountain ranges have suggested to geomorphologists that the Earth's crust can undergo rapid pulses of uplift during which rates of denudation fail to balance with rates of crustal uplift, thereby preserving much of the initial plateau topography as it rises to greater elevations. Here we analyze a regionally extensive population of mappable planar surfaces, which crown several major, tectonically active sierras of the inner south-eastern Betic Cordillera, SE Spain. Based on a synthesis of long-term landscape evolution involving landform reconnaissance, DEM-based morphometric analysis, structural geology, sediment provenance analysis, and field stratigraphy, we conclude that the summit surfaces are a mosaic of discrete, post-orogenic erosion surfaces that each developed in relation to Mediterranean marine base levels at a time when the sierras formed a series of low-elevation islands. They are not, therefore, fragments of a once regionally continuous paleoplain. The summit surfaces were partly the result of shallow-angle detachment faulting during the middle Miocene in response to lithospheric slab detachment. Where evidence exists that the resulting low-relief topography was reworked by marine abrasion during the Tortonian sea-level rise, the terminal age of the surfaces is latest Miocene. Age-bracketing based on stratigraphic correlations among the many depocentres of the region and on published thermochronological data indicates that some erosion surfaces locally formed in less than 3 million years (~ 8 Ma–5.7 Ma). They were subsequently uplifted to their current elevations (1.7 to > 2 km) by Pliocene to Quaternary neotectonics in at least two major pulses.