Calcareous nannofossil paleoecology in the sapropel S1 of the eastern Ionian sea: paleoceanographic implications

A high-resolution study performed by means of calcareous nannofossils on tw o box cores located in the South Eastern Ionian basin allowed recognition o f fluctuations in the assemblage, which can be related to the climatic and paleoceanographic changes that occurred during the deposition of the Holoce ne Sapropel S1. This study reports a decrease of the coccolith abundance an d of the genus Reticulofenestra in the S1 sapropel interval considered as w hole with its Mn and Fe oxidized intervals. Florisphaera profunda shows an increase at the base of the dark C-org rich interval, while Helicosphaera c artceri and Rhabdosphaera claviger show an increase in abundance within the Fe enriched interval of the oxidized sapropel. Braarudosphaera bigelowii i s very rare in the interval studied as a whole, however, it shows a small b ut significant increase in abundance in the Mn enriched interval of the oxi dized sapropel. Sapropel deposition is probably related to important climat ic changes that influenced the abundance of the various nannofossil species as a function of their paleoecological preferences. Our results indicate t hat three different paleoceanographic phases exist in SI, suggesting eutrop hication at the beginning of S1 deposition, followed by an intermediate sta ge characterized by nutrient depletion and, finally, by stagnation. (C) 200 1 Elsevier Science B.V. All rights reserved.