Early Pliocene closing of the Indonesian Seaway: evidence from North-East Indian Ocean and Tropical Pacific deep sea cores

Abstract

Deep sea cores from sites 214 and 758 A (Ninetyeast Ridge, north-east Indian Ocean), 761 B (Wombat Plateau, north-east Indian Ocean) and 586 B (Ontong Java Plateau, Tropical Pacific) are ideally located for comparison of late Neogene planktic foraminiferal biogeography and paleoceanographic records of tropical Indian and Pacific oceans to infer the timing of closing of the Indonesian Seaway. A consistent stratigraphy was developed between sites 214 and 586 B using graphic correlation and was integrated with the paleomagnetic time scale of Berggren et al. (1985) to provide an accurate chronology to compare interocean stratigraphic ranges of late Neogene planktic foraminifera. Tropical planktic foraminifera occur throughout each sequence at all sites. At each site the Miocene-Pliocene boundary is defined by the first appearance of Globorotalia tumida (5.2 Ma), the early/late Pliocene boundary by the first appearance of Globigerinoides fistulosus (3.2 Ma) and the Pliocene-Pleistocene boundary by the last appearance of G. fistulosus (1.6 Ma). Neogene planktic foraminiferal assemblages at sites 214, 758A, 761 B and 586B are generally similar until the beginning of the Pliocene (5.2 Ma) when the faunal record indicates divergence. A notable difference is complete absence of early Pliocene taxon Pulleniatina spectabilis from all the Indian Ocean sites. This difference suggests that the Indonesian Seaway became an effective biogeographic barrier to planktic foraminifera at the beginning of the Pliocene. However, there is still exchange of surface waters through this Seaway. Earlier studies suggested a Middle to Late Miocene occurrence for this biogeographic barrier. P. spectabilis evolved from P. primalis in the equatorial Pacific at about 5.2 Ma. It is a short-ranging early Pliocene species spanning about 1.3 my and occurred only in Pacific, unlike earlier suggestions of a broader distribution into the Indian Ocean.