Benthic foraminifera as indicators of changing Mediterranean-Atlantic water exchange in the late Miocene

Benthic foraminifera and stable isotopes from homogeneous sediments in an U pper Miocene (Tortonian-lower Messinian) cyclic succession of homogeneous m arls and sapropels from the Island of Gavdos (Greece) show significant chan ges in bottom-water oxygenation, presumably related to changes in the Medit erranean-Atlantic water exchange. The benthic foraminifera prove to be exce llent indicators of variations in the oxygen contents of the bottom waters, even more so than the stable isotopes. Our data indicate a step-wise restr iction of the Mediterranean-Atlantic water exchange resulting in increasing sluggishness of deep-water circulation. The first indication of restricted circulation is seen at 8.5 Ma, which may correspond to a severe restrictio n of the external zone of the Betic Strait, A second event, which had a ver y serious influence on the fauna in the deeper Mediterranean, occurred at 7 .16 Ma. This event was presumably linked to the partial closure of the Rifi an Corridor. The restricted Mediterranean-Atlantic connection also seems to have led to a gradual salinity increase and possibly to the formation of a brine in the deepest basins, thus marking the first development towards th e Messinian Salinity Crisis. (C) 2000 Elsevier Science B.V. All rights rese rved.