Journal of the Royal Society of Western Australia, 86(2), June 2003 
Provenance. Granitic rock fragments and fresh feldspar 
within the muddy sand and gravelly muddy sand facies 
indicate major contributions from fresh granite, with 
Mulline Formation pisolitic duricrust also contributing 
significantly to the gravelly muddy sand facies. A 
decrease in feldspar and granitic rock fragments with 
depth within the palaeovalleys may simply reflect 
increased post-depositional weathering with time. 
Alternatively, it may reflect the progressive stripping of 
weathered granite (from upper saprolite to saprock) 
associated with tectonic uplift and incision of the 
palaeovalleys. The Gibson Formation is also likely to 
have been an important source for the Nuendah 
Formation, particularly after Pleistocene arid phases 
when Gibson Formation sand-sheets would have been 
more widespread. 
Age. The landsurface component of the Nuendah 
Formation is largely of latest Quaternary (Holocene) age, 
having been deposited under present conditions of fairly 
high rainfall and seasonal drainage. The maximum age 
of the Nuendah Formation is more difficult to establish. 
However, an early Quaternary age for the base of the 
Nuendah Formation seems likely on the basis of having 
interfingering contacts with the Gibson Formation 
(interpreted as Pleistocene), and that it fills narrow 
palaeovalleys cut within broader valleys probably 
formed by epeirogenic uplift of the Great Plateau in the 
late Tertiary (?Pliocene; Jutson 1934; Bettenay & Mulcahy 
1972). 
Discussion 
Using a non-genetic lithostratigraphic approach, the 
regolith cover at East Yornaning has been subdivided 
into six major units, (1) weathered granite (mainly white 
quartz sandy kaolinitic clay with remnant granitic fabric), 
(2) weathered dolerite (mainly white slightly quartz 
sandy kaolinitic clay with remnant interstitial and 
granophyric fabric), (3) Westonia Formation (mainly light 
red clayey quartz sand becoming nodular and incipiently 
pisolitic in uppermost sections), (4) Mulline Formation 
(mainly red pisolitic sandy aluminous duricrust), (5) 
Gibson Formation (mainly light grey bimodal quartz 
sand), and (6) Nuendah Formation (mainly white muddy 
quartzo-feldspathic sand). Apart from providing a 
stratigraphic framework for future geological 
investigations of regolith within the south-western 
Yilgarn Craton, the results of this study have a number 
of important implications. 
In the absence of clear evidence of transport (cross¬ 
stratification, peat beds, basal conglomerate, truncated 
igneous structures, rounded quartz pebbles etc), it may 
be very difficult to distinguish detrital sediments from 
weathered crystalline basement. This is because regolith 
sedimentary strata are typically massive, chemically 
mature (contain only secondary or ultrastable primary 
minerals) and texturally immature (have a clay-rich 
matrix with angular and poorly sorted framework 
grains), which is very similar to weathered crystalline 
basement rock. A potential consequence of this similarity 
is for the sedimentary component of regolith to be 
underestimated. 
The sequence of Gibson Formation sand overlying 
Mulline Formation pisolitic duricrust overlying Westonia 
clayey sand, which characterises the interfluve zones at 
East Yornaning, can readily be mistaken for the sequence 
of zones produced by the in situ chemical weathering of 
Precambrian granite (Gilkes et al. 1973; Sadlier & Gilkes 
1976). This error appears to have been made by 
McArthur et al. (1977) in their mapping of the regolith in 
the East Yornaning and broader Murray River 
catchments. 
Given that the sequence of regolith strata 
(including pisolitic duricrust) situated along 
interfluve zones at East Yornaning is largely of 
sedimentary origin, it seems highly unlikely that a 
plain underlain by a "laterite" profile formed by the 
in situ weathering of Precambrian basement ("Old 
Plateau" of Jutson 1934) extended throughout the 
region, and that the present system of valleys were 
carved from it. Conceptual models of regolith- 
landscape development, based on the variable 
stripping of a regionally contiguous duricrust-capped 
weathering mantle (Woolnough 1918; Jutson 1934; 
Mulcahy 1959; Finkl & Churchward 1973; McArthur 
et al. 1977; Mabbutt 1980) are therefore not supported, 
at least within the East Yornaning area. 
As demonstrated by the distribution of the Nuendah 
Formation, water-laid sediments can be deposited along 
gently inclined valley side-slopes as well as valley floors. 
There is therefore no a priori need to invoke landscape 
inversion ( e.g. Pain & Ollier 1995) to account for ancient 
fluvial sediments, such as the basal clayey sand facies of 
the Westonia Formation, that currently occupy upper 
landscape positions. 
The regolith at East Yornaning is polygenetic, 
containing lithofacies or lithofacies components formed 
by a variety of processes {e.g. alluvial and aeolian 
deposition, in situ chemical weathering, additions and 
translocation of fines, bleaching of yellow sands by 
organic acids) that have operated at different times, 
principally under the influence of climatic and tectonic 
controls. The sedimentary regolith lithofacies are also 
largely polycyclic, having been recycled at least in part 
from pre-existing sedimentary strata. The rounded coarse 
sand-sized quartz grains at East Yornaning, for example, 
are likely to have undergone many episodes of erosion, 
transport, deposition and pedogenesis before being 
deposited in their present locations. 
Acknoivledgments: Field and initial laboratory work for this study were 
completed whilst the author was in receipt of a grant from the Rural 
Industries Research and Development Corporation (RIRDC) whilst at the 
West Australian Department of Agriculture. SEM analysis was 
undertaken at the Research School of Biological Sciences, Australian 
National University, Canberra. D K Glassford is thanked for improving 
on the quality of an early draft of this paper, and S A Wilde, C R Twidale 
and two other referees are also thanked for their many constructive 
comments. 
References 
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Regolith (ed R A Eggleton). Geological Society of Australia, 
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