PLANKTONIC FORAMINIFERAL PALEOCLIMATIC IMPLICATIONS ACROSS THE OLIGOCENE-MIOCENE TRANSITION IN THE OCEANIC RECORD (ATLANTIC, INDIAN AND SOUTH-PACIFIC)

A detailed paleoclimatic investigation was performed on planktonic for aminiferal assemblages spanning the interval from Zone P21a (late Olig ocene) to Zone N5 (early Miocene) in pelagic sequences recovered in DS DP and ODP holes in the Atlantic, South Pacific and Indian Oceans. The often rich and well preserved assemblages show that faunas fluctuate in abundance and species richness throughout the sequences. From the p ercent abundances of single taxa at different latitudes, biogeographic indices were identified. Planktonic foraminiferal distribution trends are roughly consistent with the Recent; species richness is, however, higher in upper Oligocene and lower Miocene sequence than it is today . Northern and southern Atlantic bioprovinces were delimited; the latt er is characterized by cooler climate and by species previously descri bed as endemic to New Zealand. On the basis of single species or group ed species abundance at low, middle and high latitudes, and on isotope data reported in the literature, paleoclimatic indices are identified : (1) warmer indices include Guembelitria columbiana and Gallitellia? and the Globigerinoides, Cassigerinella, Dentoglobigerina altispira, ' 'Globigerina'' ciperoensis, Globorotalia s.s. groups; (2) cooler indic es include the Globorotaloides, Catapsydrax and the Globigerina s.s. g roups and tenuitellids; (3) warm-temperate indices include the Paraglo borotalia siakensis, Paragloborotalia mayeri, Tenuitellinata angustium bilicata and Globoquadrina tripartita, Dentoglobigerina baroemoenensis , ''Sphaeroidinellopsis'' disjuncta, ''Praeglobigerinoides'' and ''Glo bigerina'' ottnangiensis groups; and (4) cool-temperate indices includ e Paragloborotalia nana, Paragloborotalia pseudocontinuosa, Globigerin a aff. praebulloides and the Zeaglobigerina woodi group. Climatic curv es were constructed for each hole. The identified positive and negativ e peaks in the climatic curves are sometimes correlative from hole to hole. General paleoclimatic trends can be summarized as follow: coolin g in Subzone P21a (late Oligocene); warming in Subzone P21b to upper Z one P22 (late Oligocene) followed by a cooling and strong climatic ins tability from the uppermost Zone P22 through Zone N4 (probably respons ible for the discrepancies in distributions of some taxa reported in t he literature across the Oligocene/Miocene boundary); and renewed warm ing from the upper part of Zone N4b into Zone N5 (early Miocene). Base d on their abundance in the upwelling zones, Paragloborotalia kugleri, Globorotaloides hexagonus, Globorotaloides stainforthi, and protentel lids were identified as upwelling indices. High abundances of these sp ecies associated with radiolarians, diatoms, and sponge spicules, allo wed identification of a major upwelling pulse in the lower part of Zon e N4.