CALCAREOUS NANNOFOSSIL BIOSTRATIGRAPHYOF UPPER CALLOVIAN-LOWER BERRIASIAN SUCCESSIONSFROM THE SOUTHERN ALPS, NORTH ITALY

摘要

Calcareous nannofossil biostratigraphy was investi-gated in uppermost Callovian-lower Berriasian sections from South-ern Alps, previously detected through magnetostratigraphy, in order to achieve an integrated stratigraphic framework valid at low latitudes. Nannofossil investigations were carried out on smear slides and ultra-thin sections, revealing generally scarce to common abundances and poor-moderate preservation of nannofloras. An exhaustive taxonomic revision was performed to unambiguously separate forms which arc transitional between two species and better delineate rapidly evolving groups. Four new species have been described: Zeugrhabdotus fluxes, Nannoconus peer, Nannoconus erbae, Hexalithus geometricus. Particular attention was paid to taxonomical aspects of primitive nannoconids, appearing and evolving across the early-late Tithonian transition and the Tithonian/Berriasian boundary intervals; the revision was also verified at DSDP Site 534A from Atlantic Ocean.