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 mayaroensis Zone p. p., Pseudotextularia deformis Zone, Guembelitria cretacea Zone, Parvularugoglobigerina eugubina Zone, Eoglobigerina eobulloides Subzone, and Parasubbotina pseudobulloides Zone 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' minutula and `Globigerina' fringa) appear just above the `boundary clay'; Parvularuglobigerina eugubina occurs a few centimeters above. A marked increase in abundance and diversity in the Tertiary planktonic foraminiferal population occurs at the base of the Eoglobigerina eobulloides Subzone.
Planktonic foraminifera turnover across the Cretaceous/Tertiary boundary in the Vajont Valley (southern Alps, Italy).
LUCIANI, Valeria
1997
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 mayaroensis Zone p. p., Pseudotextularia deformis Zone, Guembelitria cretacea Zone, Parvularugoglobigerina eugubina Zone, Eoglobigerina eobulloides Subzone, and Parasubbotina pseudobulloides Zone 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' minutula and `Globigerina' fringa) appear just above the `boundary clay'; Parvularuglobigerina eugubina occurs a few centimeters above. A marked increase in abundance and diversity in the Tertiary planktonic foraminiferal population occurs at the base of the Eoglobigerina eobulloides Subzone.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
