Journal of the Royal Society of Western Australia, 86:61-82, 2003 
Stratigraphy and origin of regolith in the East Yornaning catchment, 
south-western Yilgarn Craton, Western Australia 
P P de Broekert 
10 Carrick Street, Woodlands WA 6018 
O p.deb@optusnet.com.au 
(Manuscript received September 2002; accepted February 2003) 
Abstract 
Using a lithostratigraphic approach, the regolith within the East Yornaning catchment is 
subdivided into two major units of weathered Precambrian bedrock origin and a further four 
major units of sedimentary origin. The oldest sedimentary unit is the Westonia Formation, a 
mainly crudely stratified, light red clayey quartz sand, deposited along valley side-slopes by 
unconfined sheet-wash during the middle-late Tertiary. Unconformably overlying the Westonia 
Formation and weathered bedrock with a gradational contact is the Mulline Formation, a mainly 
dark red, pisolitic, quartz sandy aluminous duricrust. Petrographic and granulometric analyses 
indicate that the Mulline Formation is a secondary or "overprint" lithofacies, developed within 
upper sections of the Westonia Formation and weathered bedrock largely as a result of the 
allogenic addition of fine-grained quartz. Weathered basement and the Mulline and Westonia 
formations are unconformably overlain by the Gibson Formation, a dominantly light grey, massive, 
bimodal quartz sand, deposited as aeolian sand sheets during arid phases coeval with high latitude 
glaciations in the Pleistocene. Completing the sedimentary sequence and underlying most of the 
landsurface is the Nuendah Formation, a mainly grey, crudely stratified, muddy quartzo- 
feldspathic sand. The Nuendah Formation ranges in age from the present where it is forming along 
valley floors and side-slopes by fluvial and colluvial processes, through to the early Quaternary 
where it fills small palaeovalleys situated beneath the present major valley floors. The sequence of 
Gibson Formation grey sand overlying Mulline Formation pisolitic duricrust overlying Westonia 
Formation red clayey sands resembles the uppermost zones of a granitic deep weathering profile. 
Careful examination of regolith strata on a case by case basis is required for reliable interpretations 
of regolith genesis. 
Introduction 
A complex regolith covers much of the Precambrian 
bedrock along the south-western margin of the Yilgarn 
Craton in Western Australia (Simpson 1912; Prider 1966; 
Finkl & Churchward 1973; Anand & Paine 2002). Many 
aspects of the regolith in this region have been studied in 
considerable detail, including the development of 
weathering profiles over different bedrock types (Sadlier 
& Gilkes 1976; Davy 1979), the alteration of primary 
minerals at the weathering front (Gilkes & 
Suddhiprakaran 1979; Anand et al. 1985), the 
mineralogical properties of aluminous and ferruginous 
duricrusts (Grubb 1966; Anand et al. 1991), the near¬ 
surface geochemical expression of bedrock mineralization 
(Davy & El-Ansary 1986), the hydrological characteristics 
of weathered bedrock aquifers (George 1990), the 
relationship between regolith, soils and landforms 
(Mulcahy 1960; McArthur et al. 1977), and the nature and 
origin of surficial Mesozoic and Cenozoic sedimentary 
strata (Finkl & Fairbridge 1979; Salama 1997). No studies, 
however, have documented in any great detail the major 
lithological properties, stratigraphic relationships and 
origins of all regolith strata within an entire hydrological 
catchment. 
© Royal Society of Western Australia 2003 
A major advantage of including all strata in a 
geological study of the regolith is that it provides a basis 
for the distinction of units produced by the in situ 
chemical weathering of crystalline basement rock from 
those units produced by sedimentary processes. Owing 
to close similarities in texture and composition between 
weathered basement and overlying sediment, and the 
poor preservation of primary sedimentary and igneous 
structures, unconformable contacts between the two 
major regolith types may easily escape detection. 
Furthermore, as will be demonstrated here, traditional 
models used to infer regolith type and origin from 
landform and landscape position are often unsatisfactory, 
and it is only through a detailed study of regolith strata 
on a case by case basis that reliable interpretations of 
regolith genesis can be made. 
Using a non-genetic, lithostratigraphic approach 
(Salvador 1994), the regolith within the East Yornaning 
catchment is subdivided into six major units, two of 
which are interpreted to have formed by the in situ 
weathering of Precambrian bedrock (granite and 
dolerite), and four of which are interpreted to be of 
sedimentary origin. The latter are correlated with 
formations formally established by Glassford (1987) for 
sedimentary regolith in the north-eastern and central 
Yilgarn Craton. Correlations with other relevant 
lithostratigraphic schemes are, however, also considered 
for the sake of completeness. The origins and ages of the 
regolith units are also discussed. However, formational 
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