CHRONOSTRATIGRAPHIC FRAMEWORK OF THE EXTERNAL LIGURIAN UNITS (LATE CRETACEOUS, NORTHERN APENNINES, ITALY) BASED ON CALCAREOUS NANNOFOSSILS

The study of calcareous nannofossil assemblages recovered from the External Ligurian Units allows us (1) to reconstruct the distribution patterns of selected Late Cretaceous taxa, (2) to identify the biohorizons helpful in recognizing and characterizing the standard zones of Sissingh (1977), some of which have been grouped, and (3) to propose a synthesis of the ages achieved until now for the External Ligurian Units. According to the available dataset, rooted on published and unpublished data, the here proposed biostratigraphic scheme is based on 24 age-indicative taxa and 16 first occurrences, and its biostratigraphic resolution is comparable with the resolution of the scheme of Sissingh (1977), only considering FOs. Calcareous nannofossils are hence a fossil group useful to furnish a new and more complete chronostratigraphic framework of the main External Ligurian Units, helpful to better constrain the tectono-sedimentary and the geodynamic evolution of the Western Tethys Domain.