The evolution of Thirlmere lakes: a long-term sedimentary record of climate and fire dynamics in the Sydney Basin

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Australasian Quaternary Association Inc.
The Thirlmere lakes are located 40 km from the coast and are at ~300 m elevation and fall within the Greater Blue Mountains World Heritage area. The series of five lakes sit within a narrow and sinuous former river valley within the Hawkesbury sandstone with surrounding dry sclerophyll forest. Recent declines in water levels have prompted the NSW Office of Environment and Heritage to fund research about the history of Thirlmere lakes, the sub-surface characteristics and the potential frequency of past drying. This research builds on some existing work and has highlighted the extraordinary potential for the region for a long-term archive for palaeoenvironmental research.To date we have taken multiple vibracores across three lakes to depths of 7 m and we have supplemented this with some preliminary deep drilling to depths of 14 m. Our initial chronology is based on radiocarbon and OSL and we have employed a raft of geochemical and palaeoecological techniques to investigate changes through time. The lakes contain excellent organic preservation with deposition of the ‘modern’ peat environments commencing ~11 ka across two of the lakes investigated. This phase is represented by the upper 2 -3 m of organic rich peat (50% TOC). The underlying sediments are a mix of weakly bedded organic clays and oxidised clay facies that represent lake-wide drying intervals, a sequence that is repeated down profile. All five lakes are separated by alluvial sills that are comprised of medium to well-sorted sands, interbedded with organic ‘marker’ horizons that indicate these separate lakes were once joined, prior to the Last Glacial Maximum. The sandy sills that separate the lakes are derived from tributary alluvial fans accumulating progressively over the Holocene and effectively blocking and separating the lakes into their current configuration. This paper provides a preliminary overview of the chrono-stratigraphic history of Thirlmere lakes. © The Authors
Lakes, New South Wales, Australia, Evolution, Mountains, Valleys, Watersheds, Sandstones, Financing, Drill cores
Cohen, T., Marx, S., Barber, E., Forbes, M., Gadd, P., Tyler, J., Haines, H., Woodward, C., Zamora, A., Mooney, S., & Constantine, M. (2018). The evolution of Thirlmere lakes: a long-term sedimentary record of climate and fire dynamics in the Sydney Basin. Paper presented at the AQUA Biennial Conference, Canberra, 10-14 December 2018. (pp. 71).