A landscape history of the Wantabadgery area, N.S.W.
Date
1979
Authors
McConnell, Anne Denise
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Abstract
The landscape and soils of the Wantabadgery area lie on the western slopes of the Great Divide,
immediately to the north of the Murrumbidgee River, and provide both a landscape history of the
area and an insight into the mechanisms and effects of landscaping and pedogenic processes in
small,
granodiorite catchments in southeastern Australia.
The surficial materials at Wantabadgery are granodiorite-derived, except for minor isolated areas
of p a m a accession. On the basis of radio carbon dates, the surficial materials which form
colluvial hillslope mantles have been deposited since ca. 40,000 years BP, and the predominantly
alluvial valley terraces have been deposited in the last 10,000 years. On the basis of textural,
mineralogical, micromorphological and landscape analyses, these deposits and the soils formed
thereon, are considered to have been deposited under similar environmental conditions as exist at
present.
Variations in the surficial material and soil are attributed to intrinsic variations in geomorphic
micro-environment, different degrees of transportation and pedogenesis, and to the deposition of
materials from a range of sources within the area. The effects of weathering, transport,
deposition and pedogenesis are explained by a model of evolution of detritus. It has been found
that at all stages of the evolution of detritus, transport-
ational and depositional processes result in much greater textural and mineralogical modification
than pedogenesis, and all processes are strongly controlled by the nature of the granodiorite.
A model has also been constructed to explain the large scale land scape variations, e.g. the
formation of the different landscape units, terracing, variations in channel deposits,
discontinuous gullying, hillslope mantle variations and the lack of correlation between catchments.
The model proposes that landscaping occurs primarily through complex-responses and internal readjustments to the attainment of threshold states within the landscape system
or subsystems. External stimuli are not necessarily required to initiate change. In cases where
they are trigger mechanisms however, high magnitude, low frequency events are of equal or greater
importance than large scale regional changes.
Comparison with other southeastern Australian soil and landscape studies reveals that 1) landscapes and landscape instability are not reliable palaeo- climate indicators, 2) pedogenesis is similar to that on colluvial, granodiorite- derived deposits and alluvial deposits elsewhere in Australia, 3) granodiorite texture,
mineralogy and fabric exerts a strong control over the mode of pedogenesis and the resultant soil
type and features, and 4) the regional correlation of soil-stratigraphic units is of questionable
validity. Many of the problems encountered are considered to arise from problems inherent in
the scientific philosophies, theories and methodologies used in landscape analysis; and from the
way in which they are used.
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