Macroforaminifera and paleoenvironments near the Middle-Upper Eocene boundary in the Mossano section (Berici Mts., Vicenza, northern Italy)

The macroforaminiferal assemblages (mostly Nummulitidae, Discocyclinidae and Orbitoclypeidae) from the Middle-Upper Eocene boundary at Mossano (Berici Mts., Veneto, Italy) are investigated in detail. The paleoecological approach, mainly based on microfacies analysis, allowed the reconstruction of the paleoenvironments at different times.During the late Middle Eocene, the studied area was on the southeastern margin of the Lessini Shelf. In the latest Middle Eocene the sea depth was reduced to a few meters, probably during a lowstand, allowing deposition of carbonate sands with large nummulites (mainly Nummulites biedai). The global regressive event of about 39.5 Ma B.P. is therefore also recognized in this region. The sea level shallowed until the very end of the Middle Eocene, followed by a sudden deepening at the base of the Upper Eocene.A correlation between the first marls of Mossano and the transgressive sediments of the lowermost part of the Priabona stratotype is proposed. According to the recommendations of the International Stratigraphic Guide, the Middle-Upper Eocene boundary is therefore placed at the lithologic transition from limestones to marls. The terminal part of the Middle Eocene contains a low-diversity fauna, which lacks the larger nummulites and is dominated by Nummulites variolarius/incrassatus; it also includes N. chavannesi, N. ex gr. fabianii, N. stellatus, Operculina ex gr. alpina, Heterostegina reticulata. This residual fauna is composed of survivors of the late Middle Eocene biological crisis and it is not easily distinguishable from the Upper Eocene fauna.