Influence of plate tectonics on the distribution of late Palaeogene to early neogene larger foraminiferids in the Australasian region

Abstract

The distribution of late Palaeogene to early Neogene larger Foraminiferida in the Australian—Pacific region is related to climate and the interaction of tectonic plates. Biostratigraphic studies suggest that Cycloclypeus, Miogypsina and Lepidocyclina (Nephrolepidina) invaded the region during the Middle Oligocene. At this time the northern margin of Australia (New Guinea) was close enough to the Indonesian region and was warm enough to permit the larger foraminiferids to invade the Australian, New Zealand and the Solomon—Fiji Islands chain. Climatic and oceanic current factors had little influence on the larger foraminiferal distribution within the north Australian region, but strongly influenced the faunal distribution in Southern Australia and New Zealand. Of these three important genera Lepidocyclina (Nephrolepidina) shows the greatest amount of evolutionary differentiation; by the latest Early Miocene three distinct lineages can be recognised. The difference between the Australian and New Zealand faunas is reflected from biometric studies, although the non-biometric characteristics of the equatorial chambers indicate a close relationship. The equatorial chambers of the lineage from the Solomon—Fiji Islands chain indicate a more distant genetic relationship to the two other lineages. Plate reconstructions show that the island groups were well separated from the rest of Australasia; and that the presence of the Tasman Sea effectively isolated New Zealand stocks from the others.