José Ángel González Delgado

Late neogene molluscan faunasfrom the Northeast Atlantic (Portugal, Spain, Morocco)

Abstract The age of the main Neogene molluscan deposits from Lisboa, Algarve (Portugal), Sevilla, Huelva (Guadalquivir Basin, SW of Spain) to Dar bel Amri (South Rifian Basin, NW of Morocco) has been established and correlated with the global sea level changes on the basis of micropaleontological event-stratigraphic evidence. The time period ranges from the Early Tortonian to the Late Zanclean. The deposits consist of sands with levels of concentration of molluscs that are generally shell-supported, with a variable morphology and arrangement. They deposited in infralittoral environments, and are included in Transgressive Systems tracts or in Highstand Systems tracts. The taphonomic, sedimentologic and paleogeographic characteristics of most of the deposits suggest they originated by discontinuous processes of winnowing and bypassing of sediment, probably due to the action of storms in shallow waters (mainly in bay environments). From the paleoecologic point of view, a greater richness in the molluscan diversity is seen in the Pliocene outcrops with respect to the Tortonian ones. Also, there is a difference in the abundance of specimens from several families: Turritellidae and Veneridae are more abundant in Tortonian outcrops, whereas Naticidae, Nassariidae and Lucinidae are in Pliocene ones. In the Miocene deposits the filter feeding molluscs are dominant, while in the Pliocene the carnivorous, sedimentivores and scavengers are abundant as well. These changes in the trophic structure are probably related to changes in substratum, hydrodynamics, and climatic conditions from the Tortonian to the Pliocene.