EOCENE MONSOON FORESTS IN CENTRAL AUSTRALIA

The Australian Tertiary plant fossil record documents rainforests of a tropical to temperate character in south-eastern and south-western Au stralia for much of the Early Tertiary, and also shows the climaticall y mediated contraction of these rainforests in the mid to Late Tertiar y. The fossil record of Australian monsoon forests, that is semi-everg reen to deciduous vine forests and woodlands of the wet-dry tropics, h owever, is poorly known. Phytogeographic analyses have suggested an im migrant origin for some floral elements of present day monsoon forests in northern Australia, while other elements appear to have a common h istory with the tropical rainforests sensu stricto and/or the scleroph yllous flora. Early Tertiary macrofloras in northern South Australia m ay provide some insight into the origins of Australian tropical monsoo n forests. The Middle Eocene macrofloras of the Poole Creek palaeochan nel, and the ?Eocene-Oligocene silcrete macrofloras of Stuart Creek, b oth in the vicinity of modern Lake Eyre South, have foliar physiognomi c characteristics which distinguish them from both modern rainforest a nd Eocene-Oligocene floras from south-eastern Australia. Preliminary s ystematic work on these floras suggests the presence of: (1) elements not associated today with monsoon forests (principally 'rainforest' el ements, e.g. Gymnostoma, cf. Lophostemon, cf. Athertonia, Podocarpacea e, ?Cunoniaceae); (2) elements typical of both monsoon forests and oth er tropical plant communities (e.g. cf. Eucalyptus, cf. Syzygium, and Elaeocarpaceae); (3) elements likely to be reflecting sclerophyllous c ommunities (e.g. cf. Eucalyptus, Banksieae and other Proteaceae); and (4) elements more typically associated with, but not restricted to, mo nsoon forests (e.g. Brachychiton). The foliar physiognomic and florist ic evidence is interpreted as indicating a mosaic of gallery or riveri ne rainforests, and interfluve sclerophyllous plant communities near L ake Eyre in the Early Tertiary; deciduous forest components are not cl early indicated. Palaeoclimatic analysis of the Eocene Poole Creek flo ras suggests that rainfall was seasonal in the Lake Eyre area in the E ocene; however, whether this seasonality reflects a monsoonal airflow is not clear.