Journal of the Royal Society of Western Australia, 86(2), June 2003 
A 
B 
0.5 
0.4 
0.3 
0.2 
• 0.1 
0 
- 0.1 
- 0.2 
- 0.3 
- 0.4 
<U 
oo 
ra 
8 
very coarse 
- 0.5 
V 
xf 
★ Gibson Fm 
■ Nuendah Fm 
♦ Granite, upper saprolite 
x Westonia Fm. CS facies 
-f Westonia Fm, BS fades 
• Westonia Fm, NS fades 
| coarse | medium | fine 
0 0.5 1 1.5 2 2.5 3 3.5 
Mean size (MJ (|> 
1.4 
1.3 - 
.y 
-e 
=3 
J*. 
♦ 
O 
1.2 ■ 
<D 
♦♦ ♦- 
1.1- 
— 
■ 
■ 
o 
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x* .♦*. 4 
♦ 
.<2 1 - 
8 
-e 
=> 
Sc 
o 
< n 
§ 
*+■ ■ ■ 
v / 
5 0.9 - 
— 
■+J ■ +♦ 
■ x + _ 
o 
4" 
0.8 - 
-tr 
3 
■ • , x 
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& 
_ro 
+ • V ■ 
0.7 - 
★ * 
0.6 - 
0.5 - 
| moderately | 
poorly 
0.5 0.7 0.9 1.1 1.3 1.5 1.7 
Sorting (a,) <j) 
Figure 5. A: Particle size frequency distributions of framework 
quartz (and feldspar) grains in major regolith lithofacies. B: 
Bivariate plots of graphic grain size parameters after Folk (1974). 
For the Westonia Formation: CS = clayey sand to sandstone 
facies, BS = bimodal sand facies, NS = nodular sandstone facies. 
Age. The age of granite weathering at East Yornaning 
has not been determined. However, a Quaternary age for 
the (basal) saprock lithofacies seems reasonable given 
that high rates of weathering are likely to be prevalent 
within the catchment on account of its humid, temperate 
climate and appreciable topographic relief. Being further 
from the zone of primary mineral weathering, the 
formational age of granitic saprolite is likely to be much 
older, with a maximum age occurring along interfluve 
zones where the saprolite commonly lies protected from 
erosion beneath a cover of Westonia Formation sediment 
(Fig 3A). Oxygen isotope analysis indicates that granitic 
saprolite at Collie was formed during the middle-late 
Tertiary (Bird & Chivas 1989), although a major phase of 
68 
