1. Centre for Palynology and Palaeoecology, School of Geography
and Environmental Science, Monash University, Victoria 2800,
Australia.
2. Australian Nuclear Science and Technology Organization,
PMB 1, Menai, N.S.W. 2234, Australia
3. Earth Sciences, Melbourne University, Victoria, 3010,
Australia
Caledonia Fen is an unusual high altitude site (1280 m a.s.l) contained within a small enclosed basin eroded into the side slopes of the Snowy Range by a trellised tributary of the Caledonia River. The tributary differentially eroded strata of a broad syncline in the Snowy Plains Formation, after which sediments filled the depression base. These sediments provide what is likely to be a continuous pollen record through the last glacial cycle. Details of past vegetation are provided by pollen samples analysed at 4 cm intervals through the top 12 m of an 18 m sediment core taken from the centre of the site. Dating has been problematic with age reversal of AMS radiocarbon dates below the oldest date of 21,000 years BP at 1.8 m, and Uranium/Thorium dates indicating ages of 60,000 years BP at both 7 m and 17 m with a beyond 350,000 years BP date at 17.6 m. Recent OSL dates are in accord with an AMS date of 18,000 at c. 240 cm and a Uranium/Thorium date of c. 60,000 at c. 7 m. Results of OSL dating below 7 m are awaited. Previously the record to 7 m was considered most likely to cover the whole glacial cycle, but relating the recent OSL dates to AMS and Uranium/Thorium dates makes it possible that the 7 m peat band represents early Isotope Stage 3 interstadial.
The Holocene, the inferred interstadial at c. 7 m and the basal sediments at 18 m are characterized by organic sediment. The Holocene and 7 m pollen records are derived from aquatic fen vegetation and minor bog vegetation surrounded by eucalypt forest or woodland. These periods also have significant values of the understorey woody plants Pomaderris and Dodonaea and low values of Poaceae and Chenopodiaceae with Asteraceae (blunt-spined type) virtually absent. All other periods are represented by inorganic silty clays, have low eucalypt percentages and high values of Poaceae, Asteraceae and Chenopodiaceae. This indicates substantially lower temperatures and precipitation with the treeline below the altitude of the site. There are only subtle variations within these periods except for a phase of high Tasmannia, Monotoca and Epacridaceae, and occasional exciting submillenial events of probable higher temperatures. The completion of the detailed and highly sensitive record should elucidate the dynamics of alpine and forest vegetation in relation to climate and biomass burning through almost one whole glacial/interglacial cycle.
Accurate dating of the record has major implications for the assessment of past environments in southeastern Australia as a whole. It will also provide a good test of the synchroneity of climate change in the northern and southern hemispheres as the site reveals millenial/submillenial scale oscillations previously only documented for the northern hemisphere.