Journal of the Royal Society of New Zealand abstracts
An aeolian sediment pulse at c. 28 kyr BP in southern Tasmania
P. D. McIntosh1
K. Kiernan2
D. M. Price3
1Forest Practices Board, 30
Patrick Street, Hobart, TAS 7000, Australia.
2School of
Geography and Environmental Studies, University of Tasmania, Hobart,
Australia.
3School of
Earth and Environmental Sciences, University of Wollongong, NSW 2522,
Australia.
Abstract Thick aeolian deposits are uncommon in
Tasmania but a 7-m-thick aeolian deposit containing two stratigraphic
breaks, including one palaeosol, occurs as a gully infill at Cradoc
Hill, 5 km east of the lower Huon River floodplain in southern
Tasmania. The deposit was sampled at six depths for dating by
thermoluminescence (TL) techniques. The entire deposit gave TL ages in
the range 25–32 kyr BP (mean 28 kyr BP). One date of 41.4 kyr BP was
discounted as being probably erroneous. In contrast to loess deposits
of similar thickness in New Zealand, which have been dated and
correlated with entire glacial periods, the Cradoc Hill aeolian
sediments are interpreted to have been deposited in two stages over a
relatively short time. As the prevailing winds in the region are
westerly, the aeolian material is presumed to be derived from the Huon
River floodplain in the vicinity of Egg Island, when the floodplain was
occupied by a braided river; some of the sand component may also have
been derived from locally outcropping sandstone rocks. Aeolian
sediments of this age have not previously been recognised in Tasmania.
A significant climate event that might explain a short and intense
period of river aggradation and aeolian sediment supply has not been
noted in either the pollen or δ18O record. An alternative
explanation for the erosion and subsequent aeolian deposition is that
it resulted from natural or human-lit fires. Aboriginal settlement of
Tasmania began around 35 kyr BP and the earliest recorded human
settlement in the Huon catchment occurred at 28–29 kyr BP. A major
erosion event in the mid-Huon Valley also occurred at about this time
(27–29 kyr BP). Thus, Aboriginal settlement in the Huon catchment,
erosion in the mid-Huon Valley, and deposition at Cradoc Hill are
approximately contemporaneous. As older aeolian deposits are not
present at Cradoc Hill, it is suggested that Aboriginal burning of
vegetation rather than climatic influences may have caused both the
middle Huon erosion event and aggradation downstream at about 28 kyr
BP, providing a source of silt and fine sand which accumulated
downwind, together with sand from local sources, as gully-infill
sediments. We therefore suggest that as Aboriginal people reached
southern inland Tasmania they may have had an influence on landscape
stability, river morphology, and aeolian dust supply. This suggestion
requires corroboration from other sites.
Keywords aeolian deposits; loess; erosion; Last
Glacial; Aboriginal burning; Huon Valley, Tasmania; thermoluminescence;
dating
R04003; Received 24 March 2004; accepted 15 October 2004; Online
publication date 6 December 2004
Journal of the Royal Society of New
Zealand Volume 34, Number 4, December, 2004, pp 369–379
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