Planktonic foraminiferal turnover across the Cretaceous-Tertiary boundary in the Vajont valley (Southern Alps, northern Italy)

Abstract

Planktonic foraminiferal analysis of the Erto section in the Vajont valley (Southern Alps, northern Italy) reveals a relatively complete succession across the Cretaceous–Tertiary (K–T) boundary. The turnover of planktonic foraminiferal fauna was studied for a stratigraphic interval spanning the Abathomphalus mayaroensisZone p.p., Pseudotextularia deformisZone, Guembelitria cretaceaZone, Parvularugoglobigerina eugubinaZone, Eglobigerina eobullioidesSubzone, and Parasubbotina pseudobulloidesZone p. p.The extinction of most large, ornate, late Maastrichtian species occurs below a black ‘boundary clay’ (2–4 cm thick); however, part of the Late Cretaceous species, mainly heterohelicidids and hedbergellids, were found over an interval of more than 100 cm above the boundary. Although a relatively high number of species occur for the last time in the main extinction phase, the abundance of these outgoing species is less than 20% of the total population; unkeeled or weakly keeled, simple-shaped forms (heterohelicids, globotruncanellids, hedbergellids) constitute the bulk of the planktonic foraminiferal population both in uppermost Maastrichtian and lowermost Danian beds. The first Tertiary species (‘ Globigerina’ minutulaand ‘ Globigerina’ fringa) appear just above the ‘boundary clay’; Parvularuglobigerina eugubinaoccurs a few centimeters above. A marked increase in abundance and diversity in the Tertiary planktonic foraminiferal population occurs at the base of the Eoglobigerina eobulloidesSubzone.