Loess Records - Mineral Dust: A Key Player in the Earth System - page 422

16.8.4 Australia and New Zealand

Despite the proximity of the two countries, the understanding and characterization
of loess in Australia and New Zealand are vastly different, due to differences in
landscape processes, paleo- and contemporary climatic regimes, and sedimentolog-
ical nomenclature. Whereas in the generally cooler, wetter New Zealand, loess is
widespread and very well described, in Australia there is a scarcity of published
work describing “loess” and a general view that soil derived from fine-grained
aeolian sediment is quite restricted in distribution. Undoubtedly, the dominance of
the cold-climate loess paradigm throughout the twentieth century entrenched the
view that loess was largely absent from the Australian continent. But over the past
two decades, a counterview has emerged that the hitherto described “parna” (Butler
1956 ) should be regarded as clayey, hot-climate loess (Dare-Edwards 1984 ; Hesse
and McTainsh 2003 ; Haberlah 2007 ). In this chapter, parna will be regarded as fine-
grained loess.
At present on the Australian continent, there are two major wind paths emanating
from the arid interior. One of these extends in an east-southeasterly direction across
the eastern states to the Tasman Sea, and the other extends in a northwesterly
direction across Western Australia to the Indian Ocean (Fig. 16.5 a). It is along the
so-called southeastern dust path that the majority of the identified Australian loess
deposits exist. In particular, southern New South Wales and northern Victoria have
prominent areas of red, clayey, and often calcareous soil derived from clayey loess
(parna) deposits.
The fine-grained material that dominates Australian loess deposits is character-
ized by a relatively high clay content; the presence of coarse, silt-sized quartz; a
strong red to yellow color; and a variable presence of calcium carbonate. Indeed,
it is the combination of these attributes in soil profiles over a variety of lithologies
that first led Butler ( 1956 ) to identify and popularize the concept of “parna” on
the Riverine Plain. Mineralogically, these clayey loess deposits are dominated by
kaolinite, illite, and quartz (Beattie 1970 ), with inclusions of calcium carbonate
being more prevalent at the arid-semiarid western end of the deposition zone.
The current understanding of the genesis of Australian parna is that during arid
and windy glacial periods of the Quaternary, fine-grained materials were winnowed
from the sand hills, playas, and floodplains of what are now western New South
Wales, northwestern Victoria, and eastern South Australia and deposited 300-
500 km downwind as a blanket of sediment. A central tenet of this model is that
while the transported material contained considerable clay-sized particles, it was
transported in the form of silt-sized pellets accompanied by quartz companion
grains. Unfortunately, there is a dearth of reliable age estimates for loess deposits in
eastern Australia.
In New Zealand, loess mantles are widely distributed across both the North
and South Islands, with McCraw ( 1975 ) estimating that 10 % of the country's
land mass ( 26,000 km 2 ) is covered by loess at least a meter thick (Fig. 16.5 b).

The range of loess mantle thickness is 0.5-6.0 m (Eden and Hammond 2003 ), but