Foraminiferal Micropalaeontology in Adelaide 1950–1970: Correlation and Age Determination in Post-War Mapping and Subsurface Exploration

Abstract

In the 1940s the Cenozoic molluscan record was ceding to the foraminiferal as main biostratigraphic driver. The central scientific problems for the stratigraphy of the Cenozoic Erathem in southern Australia were a patchy biostratigraphic succession, very few links with the tropical IndoPacific region and the classical sections of Europe, and a fragile sense of stratigraphic relationships within and between the various sedimentary basins in southern Australia. In more specific terms the stratigraphic problems were (or were about to emerge as) the Miocene/Pliocene hiatus, the evolution of the Orbulina bioseries and the age of the Orbulina surface, the recognition and correlation of Oligocene strata, and discovering and dating fossil assemblages below the Upper Eocene. M.F. Glaessner at the University of Adelaide’s Geology Department and N.H. Ludbrook at the Geological Survey of South Australia made and led substantial progress in these matters, and Glaessner also stimulated research in foraminiferal morphology and evolutionary taxonomy.The progress occurred in feedback with shifts in scientific style and emphasis. Glaessner brought a new rigour to the recognition of microfossil assemblages and events and the relationship of bio-zones to chrono-stages. Exploiting the superb collection by W.J. Parr, A.N. Carter laid the groundwork with a biozoning of the Upper Eocene to Middle Miocene composite succession, employing a mix of benthic and planktonic events. M. Wade developed strong insights into the internal morphology of foraminiferal shells and its taxonomic significance, the relationships between morphospecies as biological species and morphospecies as pragmatic biostratigraphic tools, and correlating across the tropical-temperate transitions through the Cenozoic. J.M. Lindsay developed subsurface stratigraphic micropalaeontology in hydrogeology and engineering geology into a fine art, sharpened the delineation of the Miocene-Pliocene unconformity, did most to solve the Oligocene problem and (with Ludbrook) strengthened the Eocene-Miocene biozonation.By ~1970 there was a perceptual shift from species’ ranges, in which implicitly imperfect records are linked, to species’ occurrences including datums. The shift clarified insights into such geohistorical phenomena as climatic shifts and transgressions and regressions. It was encouraged by the first persuasive, numerically calibrated geological time scale. Micropalaeontology continued and stratigraphic horizons expanded in both institutions but the first two decades comprise a natural phase in Adelaide.