Accuracy in correlation and ecological aspects of the planktonic foraminiferal zonation of the mediterranean pliocene

Abstract

Pliocene planktonic foraminiferal assoclatlOns from Cretan, Sicilian and Calabrian sections have been studied qualitatively and quantitatively in order to evaluate the Pliocene biozonation for the Mediterranean. Six zones can be clearly distinguished and in the middle part of the Pliocene a further division into subzones is possible. However, it is often difficult to assign individual samples to one particular subzone. An investigation into the nature of the datum levels in the Mediterranean biostratigraphic scheme had to include a study of Atlantic material. It was found that all the datum levels in the Mediterranean are related with migrations of the bioprovinces in the Atlantic. Within the Mediterranean these bioevents are more or less synchronous but many of their Atlantic counterparts are not. A large climatic deterioration during the middle part of the Pliocene must have been responsible for numerous migrations in the Atlantic and indirectly for the datum levels in the Mediterranean. However, the water temperature in the Mediterranean, as can be constructed from the Orbulina diameter, was not affected by this climatic deterioration until a certain moment corresponding to a level in the upper part of the Pliocene. Laminated sapropelitic and diatomaceous sediments are regularly present in our sections. The fauna associations from these sediments indicate that stagnant conditions, which led to laminite-formation, were due to good stratification of the water column. A process of periodically increased run-off is thought to be responsible for this condition during the Pliocene.