University of Parma, Italy

Benthic foraminiferal data are presented of the Ceara Rise, ODP Leg 154, Site 926 in the western Equatorial Atlantic Ocean. The data cover part of the Middle Miocene: the time span between approximately 14.4 and approximately 8.8 Ma. During this period the Ceara Rise was, just as today, located at bathyal to abyssal water depths. Using benthic foraminiferal and geochemical data in combination with the preliminary benthic stable oxygen isotope data of Shackleton & Hall (1997) we reconstructed paleoceanographic changes and perturbations in the bottom-water environments. The abundance patterns of benthic foraminifera, notably Nuttallides umbonifera, Cibicides wuellerstorfi and Astrononion pusillum indicate cooling of the deep waters, and may constitute evidence of water masses of northern and southern provenance reaching the Ceara Rise in discrete periods during the course of the Middle Miocene. A series of oxygen isotopic excursions was reported during the Middle Miocene: so-called Mi-events, related to expansion of the Antarctic ice sheets. Of these Mi-events, we find the expression of Mi5 (astronomically calibrated at approximately 11.8-11.3 Ma in the Mediterranean) in our data as a period of perturbations of longer-lasting trends in the deep-water evolution. This period marks a prominent lithological transition at the Ceara Rise.