The Pliocene was a transitional period terminating the Tertiary and preluding the Quaternary and was characterised by major plate-tectonic motions that opened or closed gateways, thereby triggering major climatic events (Wright 2001). The palaeoenvironmental setting of Australia in the Pliocene is incomplete. However, recent study of a 110 m section of lake sediment of Pliocene age from Yallalie, south-western Australia, documents a high quality laminated lake sequence (Dodson and Ramrath 2001). Numerous sections of the core contain fine laminations, assumed to be possible annual sedimentation layers. This study examines forty two samples from 7.91 cm of laminated sediment from 133.64 to 133.72 m, representing approximately 82 years around 3 million years ago.

Samples are dominated by Allocasuarina/Casuarina and Myrtaceae, primarily Eucalyptus, pollen. Restionaceae pollen is also abundant. Other consistently occurring pollen types include Araucariaceae, Cyperaceae, Dodonaea, Euphorbiaceae, Poaceae, Restionaceae and Rutaceae types. Nothofagus, Dacrydium and Podocarpus types were also noted, as was Gyrostemonaceae. Proteaceae taxa include Banksia/Dryandra type, Grevillea, Petrophileand Xylomelum. This investigation supports that the Pliocene vegetation in south-western Australia contained a mix of diverse contemporary species and the more ancient wetter rainforest species, supporting that the climate was wetter and at least as warm as today. Biodiversity was as high as then, or even higher, than today. Continuous presence of charcoal throughout the examined sediment section of the core also indicates that fire was an important component of the environment in the region around Yallalie (Atahan 2002).

References

Atahan P (2002) Mid-Pliocene fire recurrence at Palaeolake Yallalie. Honours Thesis, Department of Geography, The University of Western Australia.

Dodson JR, Ramrath A (2001) An Upper Pliocene lacustrine environmental record from south-Western Australia - preliminary results. Palaeogeography, Palaeoclimatology, Palaeoecology 167, 309-320.

Wright JD (2001) Climate change: The Indonesian valve. Nature 411, 142-143.