Tectonic control on the palaeogeographic evolution of thrust-top basins at the active margin of the Guadalquivir Basin (central Betic Cordillera, S Spain)

Abstract

The Guadalquivir Basin is the foreland basin of the Betic Cordillera (S Spain). Closest to the orogen, several thrust-top basins evolved during the Late Miocene in the central part of the cordillera. Here, we study the Upper Miocene deposits in five of these satellite basins: Montefrío, Iznájar-Cuevas de San Marcos, Antequera, Bobadilla Estación and Teba, in order to (1) update the stratigraphic framework, (2) infer a depositional model, (3) establish the relationship between sedimentary record and tectonic context and (4) reconstruct the palaeogeography of the area during the Late Miocene. Upper Miocene sediments mostly consist of mixed carbonate-terrigenous deposits. Facies characterization allows inferring a sedimentary model corresponding to a ramp with foreshore deposits changing to a shoal belt offshore in the inner ramp. Swaley and hummocky cross-stratified deposits formed in the transition to the middle ramp, and plane parallel carbonate beds in the distal middle-outer ramp. Factory facies, dominated by rhodoliths and bryozoans, also occur in the middle-outer ramp environments. Silts and marls formed in the deepest outer ramp and basin settings respectively. Breccias accumulated at the toe of palaeocliffs and conglomerates and massive coarse sands were deposited in fluvio-deltaic systems. Conglomerates and sands were also reworked as gravity flows and redeposited offshore. Local facies include rudstones-grainstones displaying large-scale trough-cross bedding formed in a strait in Montefrío, and marls with chalky carbonates deposited in a shallow marine, sheltered lagoon with hydromorphic soils in Bobadilla Estación. The study basins evolved in an N-S compressive tectonic context responsible of the emersion of the main Betic reliefs. Concomitantly, E-W and ESE-WNW extension originated the main depocentres. The influence of the tectonic activity on the sedimentary infills is indicated by the presence of synsedimentary deformations and several diachronic unconformities, which are younger westward. Tectonism, in turn, also controlled the palaeogeographic evolution during the late Tortonian-early Messinian interval.