Calcareous nannofossil biostratigraphy and paleoenvironmental interpretation of the mediterranean pliocene

Abstract

The accuracy of the traditional calcareous nannofossil biostratigraphy of the Mediterranean Pliocene is low, because most of the zonal boundaries are defined on the presence or absence of the very rare species of the Ceratolithids and the Discoasterids. Coccolith floras of the Noelaerhabdaceae, the most common group of Neogene calcareous nannofossils, yield useful alternative markers for biostratigraphy and give a good framework for paleoenvironmental interpretatIOn. On the basis of biometrical analysis of samples from the Pliocene and Lower Pleistocene of sections on Crete and in southern Italy, five taxa of Reticulo/enestra, two taxa of Gephyrocapsa and one taxon of Emiliania are distinguished. Their quantitative record shows 12 major changes (biohorizons) in our sequences. Quantitative analysis of the Discoasterid associations resulted in distinguishing another 12 biohorizons, which are easily correlatable from Crete to South Italy; the Upper Pliocene ones are recognized in the record of deep-sea cores in the North Atlantic Ocean as well. A detailed zonal scheme of 13 Pliocene subzones is presented, based on selected Noelaerhabdaceaean and Discoasterid biohorizons. . The composition of the calcareous nannofloras in the Mediterranean Pliocene is interpreted in terms of an alternating predominance of subtropical, transitional and subpolar floral assemblages. From the pattern of change, short-term fluctuations in surface water temperature and seasonal contrast are inferred, which were superimposed on the overall climatic deterioration in the course of the Pliocene.