Journal of the Royal Society of Western Australia, 86(2), June 2003 
Table 2 
Descriptions of lithology for breakaway exposure EY2 at East Yornaning. Note that Gibson Formation sand occurs —50 m back from 
breakaway face. See Fig 2 for location. 
DEPTH (m) 
DESCRIPTION 
ROCK UNIT 
0-0.3 
0.3-0.5 
Sand; light grey, loose, framework supported, bimodal coarse and fine sand, with framework 
particles* of poorly sorted, near-symmetrical quartz**; trace microcline feldspar in finer size 
fractions and trace rounded quartz in coarser size fractions. 
Nodular clayey sand; as above, except cemented into large, highly irregular, light red nodules by 
fine sand- to silt-sized quartz, kaolinitic clay, goethite and hematite. 
Gibson 
Formation 
0.5-0.8 
0.8-2.1 
Nodular to weakly pisolitic sandstone; reddish yellow, nodular to weakly pisolitic, indurated to 
well indurated, framework supported, weakly bimodal medium and coarse sand, with framework 
particles of poorly sorted, coarse skewed quartz in a matrix of gibbsite, silt-sized quartz, highly 
disordered kaolinitic clay and goethite; minor rounded quartz in coarser size fractions; numerous 
voids between nodules and incipient pisoliths. 
Clayey sandstone; reddish yellow, crudely horizontally stratified, indurated to well indurated, 
weakly silica cemented; framework to matrix supported, clayey coarse sand, with framework 
particles of poorly sorted, near-symmetrical quartz in a matrix of highly disordered kaolinitic clay, 
gibbsite and goethite; minor rounded quartz in coarser size fractions and scattered angular pebbles 
of vein quartz at base. 
Westonia 
Formation 
2.1+ 
Granitic (upper) saprolite; white, massive, poorly indurated, matrix supported, coarse sandy clay, 
with framework particles of moderately sorted, fine skewed quartz, in a matrix of kaolinitic clay 
and mica group minerals. 
Archaean 
basement 
* Framework particles are >63 mm in size; matrix particles <63 mm in size; ** framework particle types listed in decreasing order of 
abundance. 
again forms a minor but conspicuous part of the coarse 
to very-coarse sand sized fraction. Matrix material is 
dominantly silt-sized quartz, gibbsite, goethite, hematite 
and highly disordered kaolinite. 
Structure. The clayey sand to sandstone facies is crudely 
horizontally stratified, very similar to near-modern 
deposits of Nuendah Formation muddy sand, which 
occupy the same valley-side and interfluve landscape 
positions (Fig 3A). The other facies lack primary 
sedimentary structures, but commonly contain pipes 
outlined by hematitic mottles and infilled with similar 
material to the sediment in which they occur. Similar 
structures are widespread at the Jarrahdale bauxite 
deposit and have been interpreted by Grubb (1966) to be 
infilled cavities left by the decay of ancient plant roots. 
Stratigraphic relationships. The Westonia Formation 
typically unconformably overlies weathered Precambrian 
granite and dolerite with a sharp contact. Where not 
exposed at the landsurface, it is typically unconformably 
overlain by the Gibson Formation with a sharp contact, 
or the Mulline Formation with a gradational contact over 
a vertical interval of about 0.2 m. 
Correlation. In terms of lithology, stratigraphic position 
and landscape position, the three lithofacies of the 
Westonia Formation at East Yornaning correlate most 
closely with the sandstone to muddy sandstone facies of 
the Westonia Formation as defined by Glassford (1987). 
A similarity in terms of lithology, stratigraphic and 
landscape position also exists with the ?Eocene Kojonup 
Sandstone (Churchill, in McWhae et al. 1958), although 
this sediment contains plant macrofossils, a basal 
conglomerate, and is partly feldspathic (Wilde & 
Backhouse 1977), which is unlike the Westonia Formation 
at East Yornaning or its type section. 
The Quagering Beds of Finkl & Fairbridge (1979) is an 
angular quartz sand with rounded quartz pebbles which 
is underlain by Precambrian basement, overlain by 
"laterite", and distributed as "upland residuals" along 
the Ravensthorpe Ramp south of Bridgetown. As such, it 
too may be a lithostratigraphic equivalent of the 
Westonia Formation. 
Origin. Crude primary sedimentary structures, bimodal 
grain-size distributions and rounded quartz grains all 
indicate that the Westonia Formation is sedimentary and 
was not produced by the in situ chemical weathering of 
granite. Furthermore, the Westonia Formation overlies 
dolerite dykes from which, given the large differences in 
quartz abundance and grain-size, it cannot have been 
produced by in situ weathering. 
Close similarities in terms of landscape position, 
geometry, structure and overall grain-size distribution 
between the clayey sand facies of the Westonia 
Formation and the muddy sand facies of the Nuendah 
Formation, suggest that the two units share a common 
origin, albeit widely separated in time. Since the 
Nuendah Formation ranges to the present and is 
currently forming along valley sides by a combination of 
unconfined sheet-wash and downslope creep (see below), 
it can be inferred that the basal clayey sand facies of the 
Westonia Formation formed in a similar manner. 
The combination of well-developed grain-size 
bimodality, kaolin spherites and clay-coated quartz 
grains within the bimodal sand facies of the Westonia 
Formation is suggestive of an aeolian origin (Folk 1968; 
Warren 1972; Glassford & Semeniuk 1995). Such an 
interpretation is also consistent with the lithofacies' 
patchy distribution and valley side position, with all 
aeolian cross-stratification having been destroyed by 
bioturbation (root growth, faunal burrowing etc) and the 
clayey matrix having been produced by the post- 
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