The distribution patterns of stratigraphically important calcareous nannofossils have been established in the Pliocene- Pleistocene of Site 653 sequence (Tyrrhenian Sea, Western Mediterranean). Semiquantitative and quantitative methods have been used to verify and improve biostratigraphic reliability of the nannofossil datums. Over twenty calcareous nannofossil events are considered reliable'for biostratigraphic correlations based on the results of this study. Many of these events are not used in the existing zonal schemes, which rely, for the early Pliocene, upon events not easily detectable in the Mediterranean record. The need for a local zonal scheme is stressed for attaining a reproducible and highly resolved biostratigraphic classification. The zonal scheme we suggest provides an average time resolution of about 0.5 m.y. in the Pliocene and of about 0.2 m.y. in the Pleistocene
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