Plio-Pleistocene drainage development in an inverted sedimentary basin: Vera basin, Betic Cordillera, SE Spain

Abstract

The Vera basin is one of a series of interconnected Neogene–Quaternary sedimentary basins located within the Internal Zone of the Betic Cordillera (southeast Spain). Since the Pliocene the Vera basin has been subjected to low uplift rates (11–21 m Ma − 1 ) and inverted via compressive tectonics that are related to the ongoing oblique collision between the African and Iberian plates. Within this paper the sedimentary and geomorphic response to basin inversion is explored. Sedimentary processes and environments are established for key stratigraphic units of the Pliocene/Plio-Pleistocene basin fill and Pleistocene dissectional landscape. These data are subsequently utilised to reconstruct an evolving basin palaeogeography. Fault and uplift data are employed to discuss the role of tectonically driven basin inversion for controlling the resultant palaeogeographic changes and associated patterns of drainage development. During the Early-Mid Pliocene the Vera basin was characterised by shallow marine shelf conditions (Cuevas Formation). A major palaeogeographic reorganisation occurred during the Mid-Late Pliocene. Strike-slip movement along the eastern basin margin, coupled with uplift and basin emergence created a protected, partially enclosed marine embayment that was conducive for Gilbert-type fan-delta sedimentation from fluvial inputs along the northern and eastern basin margins (Espíritu Santo Formation). The Vera basin then became fully continental and internally drained through the development of a consequent drainage network that formed following the withdrawal of marine conditions during the Late Pliocene to Early Pleistocene. Alluvial fans developed along the northern and western basin margins, grading to a bajada and terminating in a playa lake in central basin areas (Salmerón Formation). During the Early-Mid Pleistocene a switch from basin infilling to dissection took place, recorded by alluvial fan incision, a switch to braided river sedimentation and fluvial incision into the underlying basin fill sediments and basin margin mountainous topography. Fluvial incision, headwards erosion, expansion and modification of the consequent drainage network is documented within a series of up to four major inset river terrace levels and associated landforms. Fluvial incision and drainage network expansion are attributed to differential uplift and the creation of regional gradients between adjacent basins. The relatively low Plio-Pleistocene uplift rate of the Vera basin (11–21 m Ma − 1 ) in comparison to adjacent basins (Sorbas: 80–160 m Ma − 1 ; Huercal–Overa: > 50 m Ma − 1 ) resulted in a switch from internal to external basin drainage. Ancestral forms of the principal drainage systems within the Vera basin: the Ríos Almanzora, Aguas and Antas, captured basins and mountain catchment areas to the north (Huercal–Overa basin), southwest (Sorbas basin) and west (Sierra de los Filabres range). The switch from basin infilling to fluvial dissection is coincident with a phase of Early-Mid Pleistocene compressional tectonics, expressed by extensional faulting. This deformation is probably linked to accelerated strike-slip movement along the Palomares Fault Zone. The faulting is superimposed onto the longer term pattern of Plio-Pleistocene uplift and basin inversion.