Contraintes magnétostratigraphiques concernant la durée de l'interruption des communications marines en Méditerrannée occidentale pendant le Messinien supérieur

An upper Messinian stratigraphic section, about 72 m thick, and composed mainly of fine-grained sandstones and of blue marls, has been sampled near the Bouzghaïa village (Chelif basin, Algeria). A magnetic study conducted on 51 samples shows, according to the samples, one or two components of magnetization carried either by pyrrhotite and/or magnetite. Four normal polarity zones were isolated. The base of the section is composed of a normal polarity zone disturbed by mixed components of magnetization. The Messinian-Zanclian limit is characterized by a long normal polarity zone (about 210 Ka), followed by a reversed polarity zone. The top of the section constituted by blue marls of the "Trubi" Formation is characteristic of the lower Pliocene. This study allowed to precise the Messinian-Pliocene limit and the duration of the marine communications interruption in the Western Mediterranean during the upper Messinian which is here around 700 Ka. In the section the sedimentation rate is close to 4 cm/Ka.