ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

stern Australia. Earlier workers using air photos and Tm
have mapped contemporary drainage lines, extensive colluvial
plains, and eroding outcrops of ferruginous and saprolitic
materials. The Aem, which was flown for this
study, reveals considerable and previously unsuspected
character in the subsurface. A palaeodrainage system discordant
with the contemporary drainage is identifiable,
and the data are sufficiently detailed to enable reconstruction
of the geometry and flow direction associated with the
major palaeochannels. The margins of some of these palaeochannels
can be seen to be associated with breakaways
formed by ferruginous duricrusts.
Our interpretation of the available data supports the suggestion
that landscape evolution in Yilgarn has been dominated
by the impact of local scale relief inversion, facilitated
by the cementing of toeslope and valley floor materials
with iron. As relief inversion proceeds valley floor ferricretes
may become duricrusts and form breakaways in the
landscape. Whilst the relief inversion process may operate
in a similar fashion throughout the landscape over long periods
of time, and very probably continues to the present
day, the process is likely to be local and non-uniform in its
application. The ramifications of these findings for gold
exploration in the local area will be discussed.
JANET S. WRIGHT
«Desert» loess versus «glacial» loess;
quartz silt formation, source areas and sediment
pathways in the formation of loess deposits
Geography Division, Staffordshire University, Stoke-on-Trent,
Staffordshire, ST4 2DF, UK
Loess and loess-like deposits cover large parts of the
earth's land surface. It is now widely accepted that these
deposits are aeolian. However there is still some debate
about the production of quartz silt particles which are the
single most important constituent of both loess deposits
and contemporary dusts. Quartz is very common in
igneous and metamorphic rocks, but it occurs in these
rocks at a much greater mean size than in dusts and loess
deposits, for example the mean size of quartz in gneisses
and massive igneous rocks is approximately 700Mm. Therefore
the quartz component of dusts and loess deposits
has experienced a considerable reduction in size since it's
release from bedrock. It is generally assumed that the subglacial
environment is the only environment where conditions
are sufficiently energetic to comminute sand sized
and larger grains into the size range characteristic of loess
on the scale large necessary for the formation of loess deposits.
However, it is now apparent that the Sahara has
produced considerable quantities of quartz silt and results
from a series of laboratory experiments have demonstrated
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that a range of geomorphic mechanisms may be capable of
reducing sand-sized quartz to silt-sized particles. The mechanisms
investigated were aeolian abrasion, fluvial comminution'
glacial grinding, salt weathering and frost
weathering. The findings from this laboratory work indicate
that glacial grinding may not be as effective in comminuting
sound unstressed sand sized quartz particles to silt sized
particles as has generally been presumed.
Using these findings hypothetical pathways that show the
sequence of events involved in the formation of aeolian dust
particles and dust deposits will be presented. The purpose
of these will be to illustrate the potential contribution
of the geomorphic mechanisms investigated experimentally
to the production of quartz silt and hence to the formation
of loess deposits. In order to assess the feasibility of
these geomorphic mechanisms as contributors to global silt
production these hypothetical sequences of events will be
applied to a range of dust source regions and loess and silt
deposits from the natural environment. In doing this probable
event sequences for these dusts and dust deposits
will be constructed using information obtained primarily
from published sources. In the construction of these sequences
the following factors will be considered; (1) particle
characteristics of various loess and silt deposits, (2) particle
characteristic of present day dusts and contemporary
dust deposits (3) the geology of source areas, receiving
areas and the areas through which material is transported,
(4) climatic and palaeoclimatic conditions of source areas,
(5) characteristics of current subglacial debris. These sequences
will allow some conclusions to be drawn about the
role of glacial grinding, fluvial comminution, aeolian abrasion,
salt weathering and frost weathering in the production
of total global silt. This research suggests that if the
term «desert» loess is replaced by the term «non-glacial»
loess the search for a desert or non-glacial source for loess
deposits is not misguided. Limitations of this work and
suggestions for future research into the «desert» loess versus
«glacial» loess controversy will also be discussed.
KEGANG Wu
Runoff and sediment response of badland gully
to rainfall, Southern China
Department of Geography, University of Liverpool, Liverpool,
p.o. box 147, UK
Badland gully is not uncommon in the deeply weathered
saprolite that has a wide distribution in Southern China. In
Deqine County of Guangdong Province, out of 378 km 2
area effected by soil erosion (16.8 % of the total area) there
are 150.2 km 2 effected by gully erosion and 65.6 km 2 by
badland gully. There are 23,293 badland gullies in the area
effected by soil erosion, 61 gullies per km 2 on average. For-