Late Miocene stratigraphy and palaeogeographic evolution of the intramontane Guadix Basin (Central Betic Cordillera, Spain): implications for an Atlantic–Mediterranean connection

The Guadix Basin is an intramontane basin located in the central sector of the Betic Cordillera. Its Late Miocene stratigraphic record is divided into three depositional sequences limited by unconformities representing tectonic and/or eustatic events. Depositional sequence I (late Tortonian) is composed by two systems tracts. The lower marks the beginning of marine sedimentation in the basin, and comprises three retrograding lithological complexes or depositional systems (coastal, shallow platform and pelagic basin), and is interpreted as a transgressive systems tract. The upper systems tract consists of a shallow shelf prograding into a pelagic basin. This systems tract exhibits a typically regressive pattern and was deposited during high sea level, and is therefore interpreted as a highstand systems tract. Depositional sequence II (late Tortonian) is composed of both continental (alluvial cones) and shallow marine (Gilbert-type delta, shallow shelf, and reef) depositional systems. The deposits of this sequence record a significant fall in sea level and are interpreted as a lowstand systems tract. Depositional sequence III (late Turolian–Ventian or late Tortonian–Messinian) was formed of solely retrograding continental depositional systems (alluvial fan, lacustrine fan delta, mud flat, and lacustrine). With this sequence begins the continental sedimentation in Guadix Basin in an endorheic context. The palaeogeographic evolution of the Guadix Basin during the Late Miocene can thus be divided into three stages. The first corresponds to depositional sequence I and is characterised by the development of shallow marine environments on the basin margins and deep water deposits in its centre. During this stage the basin was connected to the west with the Atlantic Ocean via the Granada and Guadalquivir basins and toward the east with the Mediterranean Sea through the Almanzora and Campo Coy basins. In the second stage, represented by depositional sequence II, most of the basin was occupied by shallow marine environments. During this stage the connection with the Atlantic and Mediterranean was only open through the Guadalquivir and Campo Coy basins, respectively. Finally, the third and last stage, corresponding to depositional sequence III, is characterised by the development of continental environments throughout the basin. This stage records the definitive closing of the connections with the Atlantic Ocean and the Mediterranean Sea.