Calcareous nannofossils, planktonic foraminifera and oxygen isotopes in the late Quaternary sapropels of the Ionian Sea

Core M 25/4-12, a long piston core (12.20 m) recovered in the Ionian Sea du ring cruise M25/4 of the R/V Meteor (summer 1993) at a water depth of 2467 m, shows an almost complete sequence of sapropels (S-1, S-3 to S-10) over t he last 330 ka. This paper presents the results of an integrated study base d on quantitative biostratigraphic analyses, performed on both calcareous n annofossils and planktonic foraminifera, coupled with the delta(18)O record . A decrease in Syracosphaera? sp. 1 and an increase in the abundance of th e genus Rhabdosphaera and of Helicosphaera carteri, Florisphaera profunda a nd of the reworked specimens, has been found in the calcareous nannofossil assemblage within the sapropels. The planktonic foraminiferal assemblage of the sapropels is characterized by a peak in the frequency of Globigerinoid es ruber (var. alba and rosea) and Neogloboquadrina dutertrei. The delta(18 )O record of Globigerinoides ruber and Globigerina bulloides allows recogni tion of isotope stages 1 to 9 and shows a negative fluctuation that corresp onds to the sapropel layers. These features support the idea of increased p roductivity coupled to the presence of reduced salinity surface waters that caused the deposition of the sapropels. However, the need for a good under standing of the ecological requirements of modern assemblages is stressed. This is necessary to correctly interpret fossil assemblages. This in turn w ill allow a better understanding of the palaeoceanographic conditions leadi ng to sapropel deposition. (C) 1999 Elsevier Science B.V. All rights reserv ed.