Journal of the Royal Society of Western Australia, 86(2), June 2003 
Figure 9. A-C: Rounded, very coarse sand-sized quartz grains in 
the Westonia Formation. The rounded quartz grains were 
probably ultimately sourced from an ancient texturally mature 
(?fluviatile) sediment. A,B = sample EY61/1 optical 
photomicrographs cross-polarized light. C = sample EY61/1 
scanning electron photomicrograph. 
depositional infiltration of fine particles, possibly derived 
from aeolian dust. 
Post-depositional infiltration of fine material seems to 
have played a much more prominent role in 
development of the nodular sandstone facies of the 
Westonia Formation. In this case, large quantities of very 
fine to fine sand-sized quartz appear to have penetrated 
the uppermost part of the bimodal sand facies, or more 
commonly the clayey sand to sandstone facies (Table 2). 
Accompanying or following the influx of fine material, 
there has been a segregation of coarser and finer quartz 
grains to form nodules, which, with further 
reorganization become incipiently pisolitic. Good 
examples of this progression are shown in Fig 8B and 
Plate 1 A. 
Comparisons between thin sections and grain-size 
distributions show that the degree to which nodules are 
developed is directly proportional to the amount of fine 
sand added by infiltration. Thus, samples with a quartz 
grain-size distribution similar to that of the original 
clayey sand sediment, such as EY27/3 in Fig 5A, are only 
weakly nodular. Samples, such as EY2/2A, in which a 
fine mode and negative skew have been created by the 
addition of abundant fines, are on the other hand 
strongly nodular. Confinement of this process to the 
uppermost metre or so of the Westonia Formation only 
and the absence of broken rounded quartz grains (Fig 
8B) indicates that the "addition of fines" is not simply a 
result of in situ quartz particle breakage associated with 
weathering or pedogenesis. 
Provenance. Possible sources of the fines in the 
nodular sandstone facies of the Westonia Formation 
include (1) aeolian dust, as in the case of the bimodal 
sand facies of the Westonia Formation, (2) the 
overlying Gibson Formation, which also comprises a 
large proportion of fine to very fine sand-sized quartz 
(Fig 8C), and (3) some other overlying sediment, all 
vestige of which was removed during creation of the 
unconformity that separates the Westonia and Gibson 
formations. 
Weathered granite is likely to have been the dominant 
source-rock for the other two Westonia Formation 
lithofacies, although the reworking of a pre-existing 
texturally mature (?fluviatile) sedimentary cover is 
indicated by the presence of small quantities of well- 
rounded quartz grains. The preponderance of 
monocrystalline quartz grains, both rounded and 
angular, with numerous embayments and etch features, 
variously filled with matrix material (Fig 7C,D), further 
suggests that both source-rock types had been subjected 
to pedogenesis (Cleary & Conolly 1972; Eswaran et al. 
1975). An abrupt change to much fresher quartz grains in 
granitic saprolite immediately below the Westonia 
Formation (Fig 7A,B) indicates that pedogenic alteration 
of the quartz grains was not primarily achieved after 
deposition of the Westonia Formation. 
Age. There is no evidence that can be used to directly 
date deposition of the Westonia Formation. However, 
since the unit is extensively eroded and unconformably 
overlain by the Gibson Formation, interpreted to be 
Pleistocene, a middle-late Tertiary age seems likely. This 
concurs with a probable Eocene age for the Kojanup 
Sandstone (Wilde & Backhouse 1977) and Quagering 
Beds (Finkl & Fairbridge 1979). 
Mulline Formation 
Distribution, geometry & dimensions. As with the 
Westonia Formation, the Mulline Formation comprises 
only a small proportion of the regolith at East 
Yornaning. It forms small, dissected plateaux ("lateritic 
gravel plains") along interfluve zones and small 
rounded hills in various landscape positions. Less 
commonly, it occurs as narrow discontinuous spurs that 
extend for several hundred metres from the interfluve 
zones toward the valley floors (Fig 2). The consistent 
74 
