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 foraminiferal assemblages spanning the interval from Zone P21a (late Oligocene) to Zone N5 (early Miocene) in pelagic sequences recovered in DSDP 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. he percent 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 latter is characterized by cooler climate and by species previously described as endemic to New Zealand. basis of single species or grouped 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 indices include the Globorotaloides, Catapsydrax and the Globigerina s.s. groups and tenuitellids; (3) warm-temperate indices include the Paragloborotalia siakensis, Paragloborotalia mayeri, Tenuitellinata angustiumbilicata and Globoquadrina tripartita, Dentoglobigerina baroemoenensis, “Sphaeroidinellopsis” disjuncta, “Praeglobigerinoides” and “Globigerina” ottnangiensis groups; and (4) cool-temperate indices include Paragloborotalia nana, Paragloborotalia pseudocontinuosa, Globigerina aff. praebulloides and the Zeaglobigerina woodi group. ic curves were constructed for each hole. The identified positive and negative peaks in the climatic curves are sometimes correlative from hole to hole. l paleoclimatic trends can be summarized as follow: cooling in Subzone P21a (late Oligocene); warming in Subzone P21b to upper Zone P22 (late Oligocene) followed by a cooling and strong climatic instability from the uppermost Zone P22 through Zone N4 (probably responsible for the discrepancies in distributions of some taxa reported in the literature across the Oligocene/Miocene boundary); and renewed warming from the upper part of Zone N4b into Zone N5 (early Miocene). on their abundance in the upwelling zones, Paragloborotalia kugleri, Globorotaloides hexagonus, Globorotaloides stainforthi, and protentellids were identified as upwelling indices. High abundances of these species associated with radiolarians, diatoms, and sponge spicules, allowed identification of a major upwelling pulse in the lower part of Zone N4.