Messinian pre-evaporite sapropels and procession-induced oscillations in western Mediterranean climate

Cyclical fluctuations in planktic foraminiferal assemblages have been recog nized in the pre-evaporitic Messinian in a marginal basin of the western Me diterranean. The fluctuations coincide with a dominantly precession-control led sedimentary cyclicity (sapropels). During sapropel deposition, high pla nktic foraminiferal diversities are indicative of relatively stable marine conditions, while during homogeneous marl deposition low diversities seem t o indicate the presence of unfavourable, more saline surface water conditio ns. The dominance of a precession-related signal indicates that regional cl imate oscillations rather than (obliquity-related) glacio-eustatically cont rolled influxes of Atlantic and/or Mediterranean waters are responsible for the faunal fluctuations and sedimentary cyclicity. Our scenario links the persistence of normal marine conditions during sapropel formation with incr eased rainfall and run-off along the western Mediterranean at times that pe rihelion occurred in Northern Hemisphere summer. Less favourable, highly sa line surface water conditions prevailed during periods of drier climate ind uced by opposite precessional extremes. The cyclical oceanographic fluctuat ions could also have governed periodic reef growth along the margins. (C) 1 999 Elsevier Science B.V. All rights reserved.