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

Abstract

Core M 25/4-12, a long piston core (12.20 m) recovered in the Ionian Sea during 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 the last 330 ka. This paper presents the results of an integrated study based on quantitative biostratigraphic analyses, performed on both calcareous nannofossils and planktonic foraminifera, coupled with the δ 18O record. A decrease in Syracosphaera? sp. 1 and an increase in the abundance of the genus Rhabdosphaera and of Helicosphaera carteri, Florisphaera profunda and 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 Globigerinoides ruber (var. alba and rosea) and Neogloboquadrina dutertrei. The δ 18O record of Globigerinoides ruber and Globigerina bulloides allows recognition of isotope stages 1 to 9 and shows a negative fluctuation that corresponds to the sapropel layers. These features support the idea of increased productivity coupled to the presence of reduced salinity surface waters that caused the deposition of the sapropels. However, the need for a good understanding of the ecological requirements of modern assemblages is stressed. This is necessary to correctly interpret fossil assemblages. This in turn will allow a better understanding of the palaeoceanographic conditions leading to sapropel deposition.