FORAMINIFERAL PALEOECOLOGY AT THE TORTONIAN-MESSINIAN BOUNDARY, ATLANTIC COAST OF NORTHWESTERN MOROCCO

The Bou Regreg composite section at the western end of the Rifian Seaw ay (Atlantic side of NW Morocco) is an important reference section for the upper Miocene (Tortonian-Messinian) and Pliocene deposits of the Northeast Atlantic and the Mediterranean region because it is a contin uous, deep-marine section close to the Mediterranean, but unaffected b y the Messinian salinity crisis. The Oued Akrech section includes the lower part of this continuous marry succession, contains the Tortonian /Messinian boundary, and continues up to the time interval immediately prior to the late Messinian Mediterranean desiccation, From this sect ion, 272 taxa of foraminifera belonging to 90 genera in 17 samples hav e been identified and their ranges determined. Benthic foraminifera su pport a paleodepth estimate in the lower part of the upper bathyal zon e throughout the section. The microfaunal assemblage composition, howe ver, appears to have been significantly influenced by the Messinian co oling and by changes in the water mass structure so that differences e xist between the Bou Regreg microfaunas and Mediterranean coeval and i sobathyal assemblages. Analyses on various size fractions of the benth ic foraminiferal assemblages suggest that bed load transport mechanism s alone cannot explain the distribution patterns, and it may be assume d that either environmental pressures, such as nutrient levels, or pal eobathymetry and microhabitat preferences controlled the development o f size in at least some commonly occurring benthic species, such as An omalinoides flinti, A. helicinus, Cibicidoides mundulus, C. pachyderma , and Siphonina reticulata.