The evolution of Thirlmere lakes: a long-term sedimentary record of climate and fire dynamics in the Sydney Basin
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Date
2018-12-10
Journal Title
Journal ISSN
Volume Title
Publisher
Australasian Quaternary Association Inc.
Abstract
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
Description
Keywords
Lakes, New South Wales, Australia, Evolution, Mountains, Valleys, Watersheds, Sandstones, Financing, Drill cores
Citation
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). https://aqua.org.au/wp-content/uploads/2019/10/AQUA-2018-Program.pdf