LATE NEOGENE MOLLUSCAN FAUNAS FROM THE NORTHEAST ATLANTIC (PORTUGAL, SPAIN, MOROCCO)

The age oi the main Neogene molluscan deposits from Lisboa, Algarve (P ortugal), Sevilla, Huelva (Guadalquivir Basin, SW of Spain) to Dar bel Amri (South Rifian Basin, NW of Morocco) has been established and cor related with the global sea level changes on the basis of micropaleont ological event-stratigraphic evidence. The time period ranges from the Early Tortonian to the Late Zanclean. The deposits consist of sands w ith levels of concentration of molluscs that are generally shell-suppo rted, with a variable morphology and arrangement. They deposited in in fralittoral environments, and are included in Transgressive Systems tr acts or in Highstand Systems tracts. The taphonomic, sedimentologic an d paleogeographic characteristics of most of the deposits suggest they originated by discontinuous processes of winnoning and bypassing of s ediment, probably due to the action of storms in shallow waters (mainl y in bay environments). From the paleoecologic point of view, a greate r richness in the molluscan diversity is seen in the Pliocene outcrops with respect to the Tortonian ones. Also, there is a difference in th e abundance of specimens from several families: Turritellidae and Vene ridae are more abundant in Tortonian outcrops, whereas Naticidae, Nass ariidae and Lucinidae are in Pliocene ones. In the Miocene deposits th e filter feeding molluscs are dominant, while in the Pliocene the carn ivorous, sedimentivores and scavengers are abundant as well. These cha nges in the trophic structure are probably related to changes in subst ratum, hydrodynamics, and climatic conditions from the Tortonian to th e Pliocene.