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Slope Deposits in the Snowy Mountains, South-Eastern Australia

Published online by Cambridge University Press:  20 January 2017

A. B. Costin  and
H. A. Polach
A. B. Costin
Affiliation:
CSIRO Division of Plant Industry, Canberra, and Visiting Fellow, Department of Biogeography and Geomorphology, Research School of Pacific Studies, Australian National University, Canberra
H. A. Polach
Affiliation:
Radiocarbon Dating Laboratory, Department of Geophysics and Geochemistry, Research School of Physical Sciences, Australian National University, Canberra, Australia
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Abstract

Slope deposits in the Snowy Mountains of south-eastern Australia have a wide distribution above 1000 m elevation on slopes between approximately 5° and 25° which are well stabilized by the existing forest vegetation. The present environment is not severe enough to initiate slope instability.

The slope deposits consist of fines with gravel and angular stones showing preferred downslope orientation, overlying a generally smooth substrate of weathered bedrock. Pockets and lenses of relatively stone-free organomineral soil containing fragments of carbonized wood sometimes occur near the interface between the slope deposits and the weathered bedrock. Fragments of the carbonized wood carefully selected from three sites in different catchment areas several kilometers apart have similar radiometric ages of between 31,000 and 34,000 years.

The properties of the slope deposits and the context of the site and climatic conditions in which they now occur point to an origin under periglacial conditions commencing 31,000–34,000 years ago, associated with deep seasonal freezing and thawing although not necessarily with permafrost. It is estimated that a substantially lower mean annual temperature, at least 8–10°C less than the present, would have been necessary to produce periglacial conditions down to 1000 m in the Snowy Mountains. On the evidence of similar slope deposits elsewhere in south-eastern Australia, this major cold period was evidently widespread.

Climatic conditions prior to the onset of the cold period appear to have been generally similar to those of today, except perhaps for rather moister and cooler summers.

Type
Original Articles
Information
Quaternary Research , Volume 1 , Issue 2 , April 1971 , pp. 228 - 235
Copyright
University of Washington

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