Pliocene–Pleistocene Boundary in a South Pacific Deep-Sea Core

Abstract

THE purpose of this letter is to describe the biostratigraphy of a deep-sea core of late Pliocene to early Pleistocene age from a middle latitude area. This core contains a succession of Globorotalia tosaensis Takayanagi and Saito and Globorotalia truncatulinoides (d'Orbigny) distinctly different from that reported from tropical deep-sea sediments where it has been used to delineate the Pliocene–Pleistocene boundary. Banner and Blow^1,2 use the appearance of Globorotalia truncatulinoides in the definition of their zone N22 and state that this zone occurs in the lower part of the stratotype Calabrian. Bayliss³, however, found G. truncatulinoides to be rather rare in the type section, occurring for the first time 135 m above the base of the exposed section and 30 m above the marker designated as the base of the Calabrian by Gignoux⁴. Based on the assumption that G. truncatulinoides does in fact appear for the first time within the Calabrian, its first appearance in tropical deep-sea sediments has been taken to represent the Pliocene–Pleistocene boundary^5–7. This conclusion received support in the discovery by Berggren⁷ of a possible phylogenetic transition between Globorotalia tosaensis and G. truncatulinoides in a tropical Atlantic deep-sea core. Magnetic stratigraphy in this core indicated the age of a stratigraphically defined Pleistocene to be close to 2 million years.