EARLY TERTIARY PALEOGEOGRAPHY, LANDFORM EVOLUTION, AND PALEOCLIMATES OF THE SOUTHERN MONARO, NSW, AUSTRALIA

The age of the southern highlands of Australia has long been controversial. Recent field investigations around Bombala in southern New South Wales have shed some light on this as well as on the early Tertiary palaeoclimates in southern Australia. Late Palaeocene basalts were extruded on a landscape with a relief of at least 400 m, and possibly as much as 800 m, showing that the region had a substantial relief by the beginning of the Tertiary. Fluvial and lacustrine sediments deposited on the earlier or prebasaltic landscape have been preserved by the basalt and contain palynofloras and fossil wood, as do sediments deposited between basalt flows in the lower parts of the basalt pile. The palynomorphs are representative of the Lygistepollenites balmei Zone in the Upper late Paleocene (ca. 58-60 Ma). The pollen and fossil wood indicate the region was covered by cool temperate rainforest. Podocarps and araucarian conifers were significant components of these forests in addition to Nothofagus; ferns were prominent in some localities. The fossil wood is dominated by gymnosperms. Comparison of the palynofloras with bioclimatic data of a number of descendant extant species has shown that most belong to the mesotherm response category with mean annual temperatures in the range 14-20°C. There is little evidence that frosts were significant. Data from tree rings support this and show that climates were markedly seasonal. The annual rings are very thin suggesting cool climates. Their uniformity shows that conditions varied little from year to year. © 1990.