Mesozoic palaeogeographic evolution of the External Zones of the Betic Cordillera

Abstract

The main events characterizing the Mesozoic palaeogeographic evolution of the External Zones of the Betic Cordillera are outlined. The Triassic sediments show a 'germanic' type facies over the entire region. ending with Late Triassic evaporites and variegated clays of Keuper facies. At the beginning of the Jurassic a transgression takes place, and a broad shallow-marine carbonate-platform environment appears. During the Carixian (180) Ma) the carbonate platform breaks down leading to the differentiation of two large palaeogeographic units: the Prebetic Zone where shallow-water environments prevailed throughout the Mesozoic, and the Subbetic Zone where the sediments alc clearly pelagic. Within the Prebetic Zone, two palaeogeographic rearlms are differentiated: the External Prebetic showing important stratigraphic gaps in the Jurassic and Early Cretaceous sequence, and the lnternal Prebetic with a thicker and more continuous stratigraphic sequence. Between the Prebetic and Subbetic Zones. a palaeogeographic realm is distinguished (lntermediate units) where turtbeditic and pelagic materials were deposited. This zone corresponds approximately to a slope environment during most of Mesozoic times. In the Subbetic Zone a marked differential subsidence occurs during the Jurassic, leading to trough (Median Subbetic) and swells (External and Internal Subbetic). In the Median Subbetic, the deposits consist mainly of marls, pelagic limestones. radiolarites and calcareous turbidites, with mafic volcanic and subvolcanic rocks. During the Cretaceous pelagic marls and marly limestones were laid down. Mesozoic sedimentation took place along the southern margin of the European plate, in an Atlantic-type continental margin underlain by continental crust. Three-dimentional schemes, explaining the main palaeogeographic events are included.