Late Neogene planktonic foraminiferal biostratigraphy, Suva, Fiji

Abstract

Rich planktonic foraminiferal assemblages have been examined from about 10 samples from the well-known late Neogene marine sediments in the Suva district of Fiji. Material has been analyzed from the upper part of the late Miocene Veisari Sandstone, the early Pliocene Lami Limestone and the early to middle Pliocene Suva Marl. The planktonic foraminiferal assemblages of the upper part of the Veisari Sandstone are placed in the Globorotalia plesiotumida Zone (late Miocene). The upper part of the Lami Limestone contains Globorotalia margaritae, Globorotalia tumida tumida and rare Sphaeroidinella dehiscens immatura, an assemblage indicative of the Globorotalia margaritae Zone (early Pliocene). It is possible that the lower part of the Lami Limestone may be referable to the Globorotalia tumida tumida Zone (late Miocene) but insufficient samples did not allow this determination. The Miocene-Pliocene boundary, therefore, probably lies in the lower part of the Lami Limestone. The entire Suva Marl at least up to 50 m above the "Purple Marker" belongs to the G. margaritae Zone (early Pliocene). The early Pliocene assemblages clearly are tropical in character, while the assemblages from the upper part of the Veisari Sandstone (latest Miocene) are distinctly of cooler water affinities. The presence of cooler water assemblages at such low latitudes is probably due to upwelling of cool waters resulting from increased oceanic turnover. This is more likely related to late Miocene global cooling than to migration of cool surface waters to tropical Pacific latitudes.