CENOZOIC PLANKTONIC FORAMINIFERAL ZONATIONS OF SOUTHERN AUSTRALIA AND NEW ZEALAND

Abstract

BIOSTRATIGRAPHIC DOCUMENTATION of fossil species of planktonic foraminifera has played a major role in correlating marine Cenozoic rocks because of their relatively high diversity, abundance, rapid evolution and wide geographic distribution. A major step was undertaken in Trinidad in 1945 with the division of the Oligocene-Miocene rocks into three zones based on planktonic foraminifera and with the intensive oil-search on the island, there began an equally intensive research programme and rapid development in the study.

Two research projects, independent of each other, were initiated in Gippsland. Victoria in the 1950s which resulted in publications: (1) from surface samples, a faunal unit system was devised for the Upper Eocene-Miocene. and (2) 11 named planktonic foraminiferal zones were established in a four-foot sampled Oligocene-Miocene sequence of the Lakes Entrance oil shaft. The latter scheme was tested and expanded for 3 years during oil exploration on the East Coast of New Zealand during 1959-1962 and a further four years was spent thoroughly testing, and expanding it into 21 zones sub-dividing the whole Cenozoic time of 67my. The zones can be identified in both surface and sub-surface sections and used for direct, accurate correlations of marine rock sequences thus providing the geologist with essential data for the construction of maps and subsurface control.

The zonal scheme was re-exported back to South Australia, later to Gippsland and used there with minor local changes in the off-shore oil exploration; in 1973 the zonal scheme was further tested during the Deep Sea Drilling Project Leg 29 in the area south of New Zealand and Australia.

Studies of planktonic foraminifera and allied microfossils has resulted in the cheapest and most reliable method for rapid age determinations of Cenozoic marine rocks; in perspective it plays a minor, but essential role in oil-search. The zonal scheme is a dynamic model subject to change and improvement.