Neogene stratigraphy of the Western Guadalquivir basin (Southern Spain)

Abstract

In the Neogene sediments of the western part of the Guadalquivir Basin eight formations have been distinguished. The planktonic foraminifera in five of these formations have been attributed to seven separate planktonic faunal associations. With these lithostratigraphic and biostratigraphic data the depositional and tectonic history of the basin during the Neogene can be reconstructed. Part of the basin filling appears to be allochthonous. There is ample evidence of a marly sedimentation in the south in a bathyal environment during Late Miocene time; sedimentation may have started in the Early Miocene already. Simultaneously older Tertiary sediment masses slided into this part of the basin from the south. Early Pliocene clayey sediments in the centre and north testify of a much shallower sea depth by their lithology and foraminiferal fauna. The chaotic structure of the bathyal marl and their actual position on top of the younger clay is explained by the assumption of a northward translation of these marls, the gypsiferous Mesozoic sediments that are present below the Tertiary strata facilitating the movement. Middle Pliocene sediments, deposited over both the Late Miocene marl and the Early Pliocene clay testify of a further shallowing of the basin. In search of a section that could be considered a marine equivalent of the Upper Miocene Messinian, PERCONIGproposed the section near Carmona as stratotype for the Andalusian Stage, coeval with the Messinian stratotype and Stage. This is not substantiated by his evidence. A study of the planktonic foraminifera from the Andalusian stratotype indicates that they are homotaxial with those of the stratotypes of the Tabianian and Piacenzian Stages, of Early and Middle Pliocene Age, thus refuting its parallelisation to the Messinian, of Late 1viiocene Age.