Dune Sediment Types, Sand Colour, Sediment Provenance and Hydrology in the Strzelecki-Simpson Dunefield, Australia

165

DUNE SEDIMENT TYPES, SAND COLOUR, SEDIMENT PROVENANCE

AND HYDROLOGY I N THE

STRZELECKI-SIMPSON DUNEFIELD, AUSTRALIA R.J. WASSON*:

D e p t . o f B i o g e o g r a p h y and Geomorphology, A u s t r a l i a n Y a t i o n a l

U n i v e r s i t y , C a n b e r r a , A.C.T.,

Australia

INTRODUCTION The l a r g e S t r z e l e c k i - S i m p s o n d u n e f i e l d o f A u s t r a l i a ( F i g . 1) c o n s i s t s p r i n c i p a l l y o f l o n g i t u d i n a l dunes o f v a r i o u s k i n d s .

One o f t h e iiiost s t r i k i n g

r e g i o n a l c h a r a c t e r i s t i c s o f t h e s e dunes i s t h e i r c o l o u r ( F i g . 2 ) .

The b r i g h t

red-brown dunes o f t h e n o r t h e r n Simpson d u n e f i e l d a r e o f t e n c i t e d as b e i n g t y p i c a l o f t h i s d u n e f i e l d , b u t t h e r e a r e a l s o e x t e n s i v e a r e a s o f p a l e brown, orange brown, and w h i t e dunes.

The z o n a t i o n o f t h e s e v a r i o u s l y c o l o u r e d sands

has been i n t e r p r e t e d as t h e r e s u l t o f p r o g r e s s i v e r e d d e n i n g and a g e i n g o f sand g r a i n c o a t i n g s downwind f r o m s o u r c e s o f sand ( W o p f n e r and T w i d a l e , 1 9 6 7 ) . There a r e v a r i o u s l i n e s o f e v i d e n c e w h i c h s u g g e s t t h a t t h i s h y p o t h e s i s i s inadequate.

I n t h i s p a p e r s e d i m e n t s and m o r p h o l o g y w i t h i n each of t h e m a j o r

c o l o u r zones a r e examined, and t h e p r o c e s s e s o f s e d i m e n t m o b i l i z a t i o n f o r dune c o n s t r u c t i o n examined.

I n t h e l i g h t o f t h i s examination t h e hypothesis o f

downwind a g e i n g o f dune sand i s c r i t i c a l l y t e s t e d and f o u n d t o b e i n a d e q u a t e . SPATIAL DISTRIBUTION OF DUNE SEDIMENT TYPES Colour, i r o n c o n t e n t and m i n e r a l o g y ( f o r methods see Append'ix) Two d o m i n a n t g r o u p s o f c o l o u r s o c c u r i n t h e d u n e f i e l d ( F i g . 2 ) : brown (10YR7/4 t o 5YR6/8; (5YR6/8 t o 2.5YR4/8).

Japanese S t a n d a r d S o i l C o l o u r C h a r t ) ;

1, p a l e 2, r e d - b r o w n

N e a r t h e b i g l a k e s , w h i c h f o r m an a r c f r o m Lake Frome t o

Lake E y r e ( F i g s . 1 and 2), t h e dunes a r e p a l e c o l o u r e d .

These p a l e dunes

extend o n l y a s h o r t d i s t a n c e f r o m L a k e s Frome and C a l l a b o n n a , e x t e n d some 300 km f r o m Lake B l a n c h e , and w e l l n o r t h o f Lake Eyre.

Downwind o f t h e a r e a o f

pale dunes e a s t o f Lake Frome, a t r a n s i t i o n zone a b o u t 10-20 km o c c u r s between pale and red-brown dunes.

F u r t h e r n o r t h S t r z e l e c k i Creek f o r m s t h e b o u n d a r y

between p a l e and r e d - b r o w n dunes, a n d t h e b o u n d a r y i s as w i d e as t h e c r e e k ' s immediate f l o o d p l a i n i n some p l a c e s ;

t h a t i s , 1-2 km.

I n t h e Simpson dune-

f i e l d , t h e b o u n d a r y i s g r a d a t i o n a l , once a g a i n o v e r 10-20 km.

Apart from these

obvious b o u n d a r i e s , t h e r e a r e c o l o u r g r a d i e n t s w i t h i n t h e a r e a s o f p a l e dunes.

*

P r e s e n t a d d r e s s : C S I R O , D i v i s i o n o f W a t e r and Land Resources, P.O. Canberra City, A.C.T. 2601, A u s t r a l i a .

Box 1666,

166

Fig. 1. Simpson a n d Strzelecki dunefields, and catchments of streams entering the dunefields.

For example, sands close t o Kallakoopah Creek a r e very pale (10YR7/4) and rapidly darken t o 7.5YR7/4 in a distance of about 25 km downwind. Representative sample points a r e shown on Figure 2. Systematic sampling has been c a r r i e d out on t h r e e t r a v e r s e s within t h e dunefield (Fig. 2 ) . Traverse 1 from Moolawatana Bore t o Hawker Gate i s 140 km long and i s p a r a l l e l t o the dune trend. Each sample was taken from t h e c r e s t s of longitudinal dunes, and cons i s t s of the upper 10 cm a t each point. On Traverse 1 the sands a r e pale near Lake Frome a n d t h e i r hues redden from about 65 km downwind of Moolawatana Bore (Fig. 3 ) . Colour values show no systematic trend. Total f e l d s p a r was determined by s t a i n i n g polished sections with sodium c o b a l t i n i t r i t e a f t e r etching with hydrofluoric acid. Feldspar q u a n t i t i e s show a systematic decline from Lake Frome, b u t maintain low values from 65 km onwards. Heavy mineral content i s higher in the yellower sands near Lake Frome than in the redder sands f u r t h e r e a s t . The change in colour, t o t a l f e l d s p a r content, and heavy mineral content of c r e s t a l sands occurs a t about the same place (Fig. 3 ) .

167

Fig. 2. Dune sand c o l o u r s i n t h e Simpson and S t r z e l e c k i d u n e f i e l d s . C o l o u r s recorded a t p o i n t l o c a t i o n s a r e c o n s i d e r e d r e p r e s e n t a t i v e o f l a r g e a r e a s a r o u n d each. The c o l o u r b o u n d a r i e s a r e b a s e d on g r o u n d t r a v e r s e s , c o l o u r a e r i a l photographs, and s a t e l l i t e images. T r a v e r s e 2 ( F i g . 4 ) i s 174 km l o n g and c u t s a c r o s s t h e t r e n d o f t h e l o n g i t u d i n a l dunes ( F i g . 2).

S t a r t i n g a t t h e e a s t e r n end, t h e dunes a r e

red-brown ( d o m i n a n t hue i s 2 . 5 Y R ) Creek i s r e a c h e d a t 130 km. creek.

becoming d o m i n a n t l y 5 Y R u n t i l t h e S t r z e l e c k i

P a l e dunes ( d o m i n a n t l y 7.5YR/6)

o c c u r w e s t of t h e

A l t h o u g h t h e sample number i s s m a l l , t o t a l f e l d s p a r c o n t e n t seems t o be

168

lower in the red sands ( t h e eastern p a r t o f Traverse 2 , known as T1) t h a n in the pale sands ( t h e T2 p a r t o f Traverse 2 ) . Furthermore, the percentage of heavy minerals i s a l s o lower in the red sands t h a n in the pale sands.

H u e '5

(YR) 2.5

I

5-

-

.

Heavy minerals 0.2-

I

I 1

I

. .

*

I

.I

I

t

I

4

I

I

I

I

. . . . . . .

I.

I.

Traverse 1, Strzelecki dunefield.

Fig. 3.

Colour Value

I

. . . . .

Value 6 -

%

I

I

I

.

*

. . .

0

.

I

Location shown on Fig. 2 .

.. ... .... . ..... ... .... .... ., I. I I . , I

0..

0.0

4

0.

0.

0

0.

L

I

O %

L

"

'

4

Feldspar 2

O

(East)

Fig. 4.

.

.

0 minerals02

O

*

"

" 20

40

.

60

I

. 80

. . .

Kilometres

Traverse 2 , Strzelecki dunefield.

I

100

. , a

.I I

.I. 120

%

*. 140

Location shown on Fig. 2.

.

..

#

160 (West)

169 Traverse 3 (Fig. 5 ) i s 122 km l o n g , runs p a r a l l e l t o t h e longitudinal dunes, and s t a r t s a t the ' b i g bend' of Kallakoopah Creek in the Simpson Desert. The dune sands a r e pale near the creek, as noted e a r l i e r , becoming red-brown about 80 km downwind.

Colour values decline from south t o north. Heavy mineral content i s generally lower in the pale sands t h a n in the red sands, the reverse t o the pattern found on Traverse 2 .

Hut

I

Fig. 5.

Traverse 3 , Simpson dunefield.

Location shown on Fig. 2.

Traverse 2 was selected t o examine t h e petrographic a n d chemical differences between pale ( T 2 ) a n d red-brown ( T l ) dune sands, in a n attempt t o explain the colour differences. The following r e s u l t s were obtained: 1. The f r a c t i o n of 250 pm t o 1000 pm in diameter was separated and the grain coatings rubbed off by rubber p e s t l e in a mortar. Standard X-ray d i f fraction ( X R D ) analyses of 19 samples (13 from T1 and 6 from T 2 ) of the :oatings revealed mixtures of k a o l i n i t e , i l l i t e , and mixed-layer i l l i t e iontrnori 11 oni t e , with kaol i n i t e dominating. The only d i s c e r n i b l e difference ay in the absence of montmorillonite in some T2 samples. 2 . Chemically scrubbed and ground separations of heavy minerals from 6 iamples on T 1 and 8 samples on T2 were examined by XRD. The dominant minerals ire ilmenite, magnetite, zircon, and r u t i l e . Half t h e samples have s l i g h t l y

170 more z i r c o n t h a n m a g n e t i t e , w h i l e t h e o t h e r h a l f d i s p l a y a d e c l i n e f r o m ilmenite t o r u t i l e .

There i s no d i f f e r e n c e between T1 and T2 i n terms o f

abundant heavy m i n e r a l composition.

Four samples f r o m T1 and 3 f r o m T2 were

examined by XRD more e x t e n s i v e l y , and a l l samples c o n t a i n anatase, s p i n e l , pyroxene, hornblende, t o u r m a l i n e , topaz, g a r n e t , and a p a t i t e , w h i l e a l l samples f r o m b o t h p a r t s o f T r a v e r s e 2 c o n t a i n monazite, sphene, and a u g i t e .

3.

E n e r g y - d i s p e r s i o n X-ray (EDAX) mapping o f s e c t i o n s c u t t h r o u g h g r a i n

c o a t i n g s on two samples each f r o m T I and T2 showed random d i s t r i b u t i o n s o f t h e elements Fe, A l , S i , T i , and K.

The sample a n a l y s i s was c a r r i e d o u t on a l l

samples f r o m T r a v e r s e 2, and t h e same r e s u l t found.

From these analyses i t i s

n o t p o s s i b l e t o conclude whether t h e Fe occurs as c r y s t a l l i t e s between t h e c l a y s , o r occurs p r i n c i p a l l y w i t h i n t h e l a t t i c e s o f t h e c l a y m i n e r a l s .

4. Coatings were rubbed o f f sub-samples o f 250-1000 um g r a i n s f r o m 8 samples f r o m T1 and 6 samples f r o m T2, and t o t a l carbon determined. mean C = 81

?

40 ppm, and f o r T2 mean C = 87 i 48 ppm.

F o r T1

There i s no d i f f e r e n c e

between t h e samples, a l t h o u g h i t must be s a i d t h a t r u b b i n g abrades t h e g r a i n s u r f a c e s s o t h a t d i f f e r e n c e s between c o a t i n g s c o u l d be masked by t h e removal technique.

5.

I r o n as Fe203 was determined f o r b u l k samples ( w i t h heavy m i n e r a l s g r a i n s f o r 13 samples f r o m T1 and 6 samples f r o m T2

removed) o f 250-1000 ( T a b l e 1).

The ranges o f values c a l c u l a t e d by t a k i n g 2a about t h e means do n o t

o v e r l a p , s o t h e sample means a r e d i f f e r e n t . T1 samples t h a n i n t h e T2 samples.

That i s , t h e r e i s more i r o n i n t h e

Examination o f t h e q u a r t z g r a i n s f r o m these

samples i n t h i n s e c t i o n d i d n o t r e v e a l obvious d i f f e r e n c e s i n i m p u r i t i e s ,

it

SO

i s concluded t h a t t h e d i f f e r e n c e s d e t e c t e d i n Fe% r e f l e c t d i f f e r e n c e s i n t h e i r o n content o f t h e g r a i n coatings.

6.

Haematite was r e c o r d e d by XRD analyses i n s e v e r a l samples f r o m b o t h T1

and T2, b u t g e n e r a l l y c r y s t a l l i n e i r o n m i n e r a l s were n o t d e t e c t e d . l i k e l y t o be i n t h e Fe+3 f o r m (Walker, 1979).

A l l iron is

T h i s p r o p o s i t i o n was t e s t e d f o r NO

t h r e e samples from each o f T1 and T2 by d e t e r m i n i n g t o t a l Fe and t h e n Fet3. Fe”

was d e t e c t e d by d i f f e r e n c e . 7.

Examination o f t h i n s e c t i o n s f r o m T1 and T2 shows t h a t g r a i n c o a t i n g s

a r e g e n e r a l l y t h i c k e r i n T1 samples.

Maximum t h i c k n e s s i n T1 g r a i n s i s about

35 urn, w h i l e on T2 t h e y a r e about 10-15 urn. c o a t i n g s i n T1 i s g r e a t e r t h a n f o r T2.

T h i s suggests t h a t t h e volume of

To t e s t t h i s p r o p o s i t i o n c o a t i n g s were

rubbed o f f and t h e i r w e i g h t determined as a p r o p o r t i o n o f t h e b u l k 250-1000 sub-sample f r o m T1 samples and T2 samples. 0.75% and f o r T2 0.38

k

0.17%.

F o r T1 t h e mean v a l u e i s 0.88

*

The range o f v a l u e s f o r 2a about t h e means

o v e r l a p s , so t h e samples a r e n o t d i f f e r e n t .

T h i s r e s u l t may have been caused

by t h e i n a c c u r a c y o f t h e r u b b i n g method, o r i t may be r e a l .

Sonic removal o f

c o a t i n g s ( c f . Walker, 1979) i s o b v i o u s l y a more e f f i c i e n t method.

171 The s i g n i f i c a n t r e s u l t t o emerge f r o m t h e s e analyses i s t h a t t h e redness o f the dune sands i s a f u n c t i o n o f t h e i r o n c o n t e n t o f t h e g r a i n c o a t i n g s .

This

r e s u l t i s d e r i v e d o n l y f r o m T r a v e r s e 1, and so i t was t h o u g h t d e s i r a b l e t o t e s t i t elsewhere.

The same a n a l y s i s was c a r r i e d o u t on T r a v e r s e 3 ( T a b l e l ) , and

i t i s c l e a r t h a t t h e r e d sands have more i r o n t h a n t h e p a l e sands.

TABLE 1 Loca 1 i t y

%Fe

(x

?

s)l

Traverse 1 : T1

0.26 t 0.06

T2 : pale red Curdlawidny : p a l e red

0.18 t 0.03 0.14 ? 0.06 0.41 ? 0.04 0.34 t 0.04 0.56 i 0.04

Traverse 3

2

Coat m i n e r a l ogy2

K a o l i n i t e , i l l i t e : mont., haemati t e K a o l i n i t e , i l l i t e : mont., Haematite, k a o l i n i t e , i l l i t e Haematite, k a o l i n i t e , i l l l i t e Haematite, k a o l i n i t e , i l l i t e Haematite, k a o l i n i t e , i l l i t e

Sample no. (n 1 13 6 3 3 8 8

Mean t s t a n d a r d d e v i a t i o n , as w e i g h t % b a s i s on 250-1000 fraction. Determined by X-ray d i f f r a c t i o n on c o a t i n g s rubbed o f f 250-1000 fraction. Another t e s t was c a r r i e d o u t i n t h e P a r a k y l i a d u n e f i e l d o f South A u s t r a l i a , j u s t west o f Lake Torrens, i n t h e v i c i n i t y o f Curdlawidny Lagoon ( F i g . 6 ) . lake i s bounded by t h r e e r i d g e s which p a r a l l e l t h e l a k e ' s e a s t e r n shore.

The These

ridges a r e l u n e t t e - l i k e and a t l e a s t t h e upper 1-2 m c o n s i s t s o f a e o l i a n sand.

-dune

crest

Fig. 6. Map of dunes downwind o f t h e s o u t h e r n p a r t o f Curdlawidny Lagoon. Sample p o i n t 1 i s i n pale-brown dunes, and 2 i s i n red-brown dunes.

172 L o n g i t u d i n a l dunes e x t e n d downwind f r o m t h e s e t r a n v e r s e r i d g e s .

The sands o f

t h e t r a n s v e r s e r i d g e s and a d j a c e n t l o n g i t u d i n a l dunes a r e p a l e (2,5YR6/6), w h i l e t h e l o n g i t u d i n a l dunes f u r t h e r downwind, and n o t a t t a c h e d t o t h e t r a n s v e r s e r i d g e s , a r e r e d - b r o w n (10YR5/5). F o u r samples were t a k e n f r o m t h e c r e s t s o f one p a l e and one red-brown l o n g i t u d i n a l dune a t C u r d l a w i d n y ( F i g . 6 ) , and each sample was s p l i t .

The Fe

c o n t e n t o f t h e p a l e sand and r e d sand i s d i f f e r e n t u s i n g t h e 2 0 c r i t e r i o n ( T a b l e l ) , t h a t i s , r e d sands c o n t a i n more Fe t h a n p a l e sands.

As n o t e d e a r l i e r , d i f f e r e n c e s i n c o l o u r o c c u r w i t h i n a r e a s d e s i g n a t e d as p a l e o r red-brown.

On T r a v e r s e 3, sand hue r e d d e n s t o w a r d s t h e n o r t h , a t r e n d

which i s p a r a l l e l e d by decreasing c o l o u r value (Fig. 5).

Total i r o n content i s

n o t o n l y h i g h e r i n t h e r e d d e r sands b u t t h e r e i s a t r e n d o f i n c r e a s i n g i r o n content towards t h e north.

That i s , i r o n i s p o s i t i v e l y c o r r e l a t e d w i t h b o t h

c o l o u r and d i s t a n c e f r o m K a l l a k o o p a h Creek.

On T r a v e r s e 1, hue y e l l o w s w i t h i n

T 1 a b o u t 40 km f r o m t h e e a s t e r n end, and t h e n y e l l o w s a g a i n a t S t r z e l e c k i Creek i n t o T2 ( F i g . 4 ) .

These s t e p - l i k e changes i n hue a r e p a r a l l e l e d b y s t e p - l i k e

increases i n c o l o u r value.

T o t a l i r o n c o n t e n t a l s o p a r a l l e l s t h e s e changes i n

c o l o u r , so t h a t i r o n p e r c e n t a g e i s h i g h e s t where hue i s m o s t r e d , t h e n a t 40 km i r o n c o n t e n t f a l l s as hue y e l l o w s , and i r o n c o n t e n t i s l o w e s t where hue i s l e a s t red.

N o t o n l y a r e c o l o u r and i r o n c o n t e n t c o r r e l a t e d between m a j o r zones

o f d i f f e r e n t c o l o u r , b u t s u b t l e changes i n c o l o u r and i r o n c o n t e n t p a r a l l e l each o t h e r w i t h i n each zone. The r e s u l t s p r e s e n t e d i n F i g u r e s 3, 4, and 5 i n d i c a t e t h a t t h e dune sands a r e f a i r l y homogeneous i n t h e i r h e a v y m i n e r a l c o n t e n t , b u t a s i g n i f i c a n t d i f f e r e n c e o c c u r s between T r a v e r s e 1 and 2 i n f e l d s p a r c o n t e n t .

This order o f

m a g n i t u d e d i f f e r e n c e i n f e l d s p a r c o n t e n t between t h e p a l e sands o f t h e t w o traverses i s hard t o i n t e r p r e t i n isolation, but i s l i k e l y t o r e f l e c t a difference

i n t h e s e d i m e n t s f r o m w h i c h t h e dune sands were d e r i v e d .

Grain-size Samples were t a k e n f r o m f l a t p o r t i o n s o f dune c r e s t s o n T r a v e r s e 1 and s i e v e d a t 0.25 fl i n t e r v a l s w i t h o u t t r e a t m e n t o t h e r t h a n oven d r y i n g . t h e g r a p h i c mean

Values o f

(MZ) and i n c l u s i v e g r a p h i c s t a n d a r d d e v i a t i o n (Q,) were c a l -

c u l a t e d u s i n g t h e methods o f F o l k ( 1 9 6 8 ) .

A t t h e 90% c o n f i d e n c e l e v e l , v a l u e s

o f MZ f o r T2 c a n be a p p r o x i m a t e d b y t h e normal d i s t r i b u t i o n , b u t T 1 i s b i m o d a l .

As a consequence, MZ v a l u e s f o r T 1 and T2 were compared u s i n g t h e nonp a r a m e t r i c Mann-Whitney U t e s t .

T h i s t e s t showed t h a t a t p <0.00003 t h e

samples o f MZ f r o m T 1 ( n = 4 3 ) and T2 ( n = 1 9 ) a r e n o t f r o m t h e same p o p u l a t i o n , and m o s t of T2 i s f i n e r - g r a i n e d t h a n m o s t o f T1.

U s i n g t h e same t e s t t h e r e i s

173 no s i g n i f i c a n t d i f f e r e n c e between t h e f i r s t p a r t o f T 1 ( 0 - 4 6 km) and t h e second p a r t (46-130 km) f o r w h i c h c o l o u r and heavy m i n e r a l c o n t e n t d i f f e r e d . A t t h e 90% c o n f i d e n c e l e v e l , v a l u e s o f Q,

by t h e normal d i s t r i b u t i o n . between t h e means o f

Using a t - t e s t ,

f o r T 1 and T2 c a n b e a p p r o x i m a t e d t h e r e i s no s i g n i f i c a n t d i f f e r e n c e

Q, f o r t h e t w o p a r t s o f T r a v e r s e 2 ( c f . F i g . 7 ) .

Samples w e r e c o l l e c t e d f r o m t h e Simpson d u n e f i e l d f o r p u r p o s e s o t h e r t h a n t h e c o m p a r i s o n o f sands o f d i f f e r e n t c o l o u r .

Therefore, a formal s t a t i s t i c a l

a n a l y s i s l i k e t h a t f o r T 1 and T2 c a n n o t b e c a r r i e d o u t i n t h e Simpson, b u t some comparisons c a n b e made.

Figure 7 i s a bivariate

sands f r o m t h e S i m p s o n - S t r z e l e c k i D u n e f i e l d .

M Z /Q, d i a g r a m f o r c r e s t a l

There i s v e r y l i t t l e d i f f e r e n c e

i n t h e r a n g e o f Q, f o r t h e t h r e e f i e l d s o f p o i n t s , and t h e r e i s no sound e v i d e n c e o f a r e l a t i o n s h i p between Q

and M Z' I As a l r e a d y seen, t h e b u l k o f T 1 i s c o a r s e r t h a n t h e b u l k o f T2.

The s p r e a d

o f d a t a f r o m t h e Simpson d u n e f i e l d shows t h a t t h e b u l k o f t h e s e d a t a o v e r l a p with both Strzelecki fields.

However, t h e f i n e s t c r e s t a l sands i n t h e e n t i r e

S i m p s o n - S t r z e l e c k i D u n e f i e l d o c c u r i n t h e Simpson n e a r K a l l a k o o p a h Creek, n e a r Lake Eyre, and o n t h e f l o o d p l a i n o f t h e D i a m a n t i n a R i v e r n e a r B i r d s v i l l e . A p a r t f r o m one Simpson d u n e f i e l d sample (MZ=1.54),

t h e c o a r s e s t dunes sampled

o c c u r a t t h e e a s t e r n end o f T1.

I t i s e v i d e n t from F i g . 7 t h a t t h e r e i s no a b s o l u t e s e p a r a t i o n o f c r e s t a l sands a c c o r d i n g t o g r a i n - s i z e and l o c a t i o n i n t h e d u n e f i e l d .

However, t h e r e i s

a t e n d e n c y f o r f i n e sands t o o c c u r n e a r t h e modern c h a n n e l s o f Cooper Creek (TZ), t h e D i a m a n t i n a r i v e r , and K a l l a k o o p a h Creek. a l l pale coloured.

These f i n e dune sands a r e

The c o a r s e r c r e s t a l sands t e n d t o o c c u r away f r o m t h e

modern c h a n n e l s and a r e g e n e r a l l y red-brown.

O f course t h e r e i s a l a r g e area

o f o v e r l a p where b o t h p a l e and r e d - b r o w n sands have s i m i l a r

MZ v a l u e s .

I f a l l t h e sands o f t h e Simpson d u n e f i e l d , f o r example, were d e r i v e d f r o m t h e c h a n n e l s n e a r L a k e E y r e , t h e n t h e t e n d e n c y t o c o a r s e n i n g downwind i s impossible t o e x p l a i n w i t h o u t l o c a l c o n t r i b u t i o n s during migration o f t h e dunes.

A b e t t e r explanation o f t h e grain-size data l i e s i n t h e granulometry o f

t h e s e d i m e n t s w h i c h l i e c l o s e t o t h e sampled dunes.

I n t h e area o f Kallakoopah

Creek t h e a l l u v i u m l y i n g b e n e a t h tk dunes and i n t e r d u n a l s w a l e s i s d o m i n a n t l y f i n e sand, whereas t h e a l l u v i u m a t t h e n o r t h e r n end o f T r a v e r s e 3 i s a m i x t u r e o f c o a r s e and f i n e sand.

F u r t h e r m o r e , i t w i l l b e a r g u e d b e l o w t h a t t h e dunes

themselves p r o v i d e l i t t l e e v i d e n c e o f l o n g - d i s t a n c e t r a n s p o r t o f sand b y w i n d ,

so t h e dunes have been d e r i v e d f r o m a g r e a t many l o c a l s o u r c e s o f sand. Clay P e l l e t s E x a m i n a t i o n o f t h i n s e c t i o n s o f c r e s t a l sands f r o m T 1 and T2 shows t h a t c l a y p e l l e t s ( F i g . 8 ) o c c u r i n t h e p a l e sands o f T2 b u t n o t i n t h e r e d - b r o w n sands o f T1.

174

The p e l l e t s c o n s i s t of sand-size aggregates of c l a y , s i l t a n d very f i n e sand s i z e p a r t i c l e s , which form p a r t o f the creep and s a l t a t i o n load of aeolian t r a n s p o r t . I n Australia clay p e l l e t s have been described by Bowler (1973), Butler (1974), Rhodes (1980), Dare-Edwards (1979; 1982) from both inland a n d coastal s i t e s . I n the i n t e r i o r sand-size p e l l e t s p r i n c i p a l l y form l u n e t t e s , t h a t i s , lunate transverse dunes on t h e downwind margins o f lakes.

-j

T1

n =44

T2

n :20

SimDson

I

0

0.2

0.4 0 1

(44

0.6

L

0.8

J

1.0

Fig. 7 . Mean grain-size ( M Z ) versus s o r t i n g ( Q , ) f o r c r e s t a l sands from longitudinal dunes in t h e Simpson a n d Strzelecki dunefields.

175

F i g . 8a. P h o t o m i c r o g r a p h o f q u a r t z sand and f i n e - s a n d s i z e c l a y p e l l e t s f r o m t h e L a s t G l a c i a l Sand i n M1. P l a i n l i g h t .

F i g . 8b.

As i n 8a b u t u n d e r p o l a r i z e d l i g h t .

176 The s a n d - s i z e c l a y p e l l e t s a r e g e n e r a l l y sub-rounded t o s u b - a n g i r l a r , sub-spherical

(cf.

F i g . 9 and 1 0 ) .

and

The c l a y f r a c t i o n o c c u r s as plasma w i t h a

f l e c k e d e x t i n c t i o n p a t t e r n under p o l a r i s e d l i g h t .

I n a f e w cases c l a y o c c u r s

as o p t i c a l l y o r i e n t e d c o a t i n g s ( c u t a n s ) on s i l t - s i z e p a r t i c l e s w i t h i n t h e pellets.

M i c r i t i c c a l c i t e o c c u r s w i t h i n t h e plasma on r a r e o c c a s i o n s .

F i g . 9. S c a n n i n g e l e c t r o n m i c r o g r a p h o f a modern c l a y p e l l e t f r o m Lake E y r e . Sample s u p p l i e d b y J . D u l h u n t y . I n t h i n s e c t i o n s o f c r e s t a l sands f r o m T2, c l a y p e l l e t s c o n s t i t u t e u s u a l l y l e s s t h a n 5'4 (number f r e q u e n c y ) and a l w a y s l e s s t h a n 12%.

Clay p e l l e t s a l s o

o c c u r w i t h i n t h e p a l e sands o f t h e s o u t h e r n 8 0 km o f T r a v e r s e s 1 and 3 , t h e t r a n s v e r s e dunes on t h e downwind edges o f Lakes Frome, B l a n c h e and E y r e , i n t h e c r e s t s o f l o n g i t u d i n a l dunes t o t h e e a s t o f Lake E y r e and on t h e f l o o d p l a i n of t h e Diamantina R i v e r near B i r d s v i l l e .

S e v e r a l dunes were sampled t o t h e n o r t h

o f Cooper Creek i n t h e p a l e dune p a r t o f t h e S t r z e l e c k i d u n e f i e l d , and once a g a i n c l a y p e l l e t s were f o u n d i n t h i n s e c t i o n s . T h i n s e c t i o n e v i d e n c e d e m o n s t r a t e s t h a t t h e c r e s t s of t h e p a l e dunes c o n t a i n c l a y p e l l e t s , u s u a l l y i n q u a n t i t i e s l e s s t h a n 5%.

Samples examined f r o m t h e

r e d - b r o w n dunes on T1 ( T r a v e r s e 2 ) , T r a v e r s e s 1 and 3 , f r o m t h e n o r t h w e s t e r n and s o u t h w e s t e r n Simpson d u n e f i e l d n e a r Andado and M o k a r i b o r e r e s p e c t i v e l y , show t h a t c l a y p e l l e t s do n o t o c c u r i n t h e s e sands.

C l a y f l a k e s (Dare-Edwards,

1982) o c c u r i n b o t h r e d - b r o w n and p a l e dunes, c o n s i s t i n g o f p a r a l l e l l a m i n a e o f w e l l - o r i e n t e d c l a y ( c f . Wopfner and T w i d a l e , 1967, p . 1 3 2 ) .

177

Fig. 10a.

Photomicrograph of modern p e l l e t s from Lake Eyre.

Fig. l o b .

A s f o r 10a b u t under p o l a r i z e d l i g h t .

Plain l i g h t .

178 The i n t e r i o r s o f b o t h p a l e and red-brown dunes have been examined i n d e t a i l a t a few l o c a t i o n s , b u t one s i t e near Moomba camp i n t h e S t r z e l e c k i serves t o i l l u s t r a t e t h e main c h a r a c t e r i s t i c s o f t h e p a l e dunes.

A t s i t e M 1 ( F i g s . 11

and 12) t h e p e r i o d i c a l l y m o b i l e cap t o t h e dune has accumulated on t h e western f l a n k as w e l l as on t h e c r e s t o f t h e dune.

T h i s cap (some 200 cm t h i c k ,

F i g . 12) o v e r l i e s , w i t h a sharp boundary, tough sandy sediment which a l t e r n a t e s w i t h s o f t e r sands u n t i l a t about 530 cm a n o t h e r sharp break occurs. sediment below t h i s break i s r e d d e r between 530 and 640 cm (7.5YR7/6)

The than t h a t

above and, a t about 820 cm, c o n t a i n s pedogenic c a l c i t e nodules and r o o t pseudomorphs o f l i k e l y pedogenic o r i g i n .

The reddened sand i n t h e upper p a r t

o f t h i s u n i t , and t h e carbonate nodules, a r e evidence o f weak pedogenesis.

The

sharp break a t 530 cm i s i n t e r p r e t a t e d , t h e r e f o r e , as a diastem.

West

East

Moomba Ck Fig.l2+

,

.

.

.

O

0Mobile cap

40 m

Last Glacial sand

Coarse sandy alluvium

F i g . 11. C r o s s - s e c t i o n o f a l o n g i t u d i n a l dune j u s t e a s t o f Moomba Camp, S t r z e l e c k i d u n e f i e l d . T h i s i s t h e s i t e of M 1 ( F i g s . 12 and 1 7 ) , l o c a t e d i n a p i t dug on t h e western f l a n k o f t h e dune. Twigs and l e a f d e b r i s b u r i e d a t ca. 200 cm gave a 14C age* o f 116% modern (ANU-2199), which i s a d a t e o f l a t e 1950s. O t h e r m o b i l e caps t o dunes i n t h e Moomba area c o n t a i n backed blades, stone a r t i f a c t s which were produced d u r i n g t h e l a s t 4000 y r s .

T h e r e f o r e , some caps c o u l d be s e v e r a l thousand y e a r s o l d .

The t o u g h e r sand between 210 and 530 cm i s c o r r e l a t e d w i t h t h e l a s t m a j o r phase o f f i n e - g r a i n e d a l l u v i a t i o n by Cooper Creek.

14C dates on t i n y c h a r c o a l p a r -

t i c l e s p l a c e t h i s phase o f a l l u v i a t i o n and, by c o r r e l a t i o n and d a t i n g , a e o l i a n a c t i v i t y between 13,000 and 23,000 y r s . B.P.

1 4 C d a t e s , on c h a r c o a l b u r i e d

i n t h e t o p o f t h i s same dune sand ( s t r a t i g r a p h i c a l l y e q u i v a l e n t t o ca. 210300 cm i n M1;

*

F i g . 1 2 ) , a r e 13850+190 (ANU-2278) and 13150k830 (ANU-2279).

A l l 14C d a t e s i n t h i s paper a r e u n c a l i b r a t e d .

179

a

%

Thin

(+

SIC1 05 Oi LLU

sections

a

pellets

0

12

U

7

0

9 O E

0

____ 0

P

a

P

m

i

a a

a

0

6

0

11

0

62

-o

28

0

24

0

a a -

0

a

0

a

P

0

a

I

a a

0

a

0

a

a

a

a

m

m

a

0

50

0

33

0

39

0

5

a

4

3 +

0

a

E

0

I

a

-

a

0

0

0 1

m

a

19

o

-

a

a

a

I

m

a

a

a

C m

-0

0

a

a

:

E

0

0

m

a

nodules

Fig. 12. S t r a t i g r a p h i c d i a g r a m o f m o s t e a s t e r l y p a r t o f t h e M 1 p i t . l o c a t i o n see F i g . 11.

For

180 T h i s c o n f i r m s t h e c o r r e l a t i o n , t h e b a s i s f o r w h i c h w i l l be e x p l a i n e d b e l o w . The a e o l i a n sand between 210 and 530 cm i n M 1 i s t h e r e f o r e o f L a s t G l a c i a l age, and was d e p o s i t e d a t t h e peak o f t h a t g l a c i a l p e r i o d ( c f . S a r n t h e i n , 1 9 7 8 ) . The a e o l i a n sand b e l o w 530 cm i s o b v i o u s l y v e r y much o l d e r t h a n 23,000 y e a r s , as evidenced by t h e d i a s t e m discussed e a r l i e r . T u r n i n g now t o t h e s e d i m e n t s o c c u r r i n g i n M1, i t i s c l e a r t h a t t h e tnacroscopic features observable i n t h e f i e l d c o r r e l a t e w i t h microscopically determined c h a r a c t e r i s t i c s .

The number f r e q u e n c y o f c l a y p e l l e t s has been

d e t e r m i n e d i n t h i n s c , - t i o n s b y p o i n t c o u n t i n g 400 g r a i n s i n each s l i d e . g r a i n - s i z e c h a r a c t e r i s t i c s w e r e d e t e r m i n e d b y d r y s i e v i n g a t 0.25

0

a f t e r g e n t l e d i s a g g r e g a t i o n w i t h a r u b b e r p e s t l e and oven d r y i n g .

The

intervals

F i v e samples

were t r e a t e d b y u l t r a s o n i c d i s p e r s i o n ( s e e a p p e n d i x ) and t h e samples d r y s i e v e d t o 4 0 and t h e n p i p e t t e d .

The r e s u l t s a r e s e t o u t i n T a b l e 2.

TABLE 2 Sampl e no.

M1/3 M1/13 M1/23 M1/33 M1/45

No d i s p e r s i o n

%14 0

Q,

MZ

2.32 2.15 2.17 2.32 2.01

0.37 0.46 0.42 0.51 0.58

0.01 0.02 0.04 1.20 0.8

U1 t r a s o n i c a l l y d i s p e r s e d Q, 70<4 0 4<9 0 MZ

2.45 2.3 2.52 2.46 2.25

0.6 0.74 4.02 3.33 1.06

6.07 5.99 13.72 11.60 10.42

Pellets

1.78

10 8 60 17 42

0

8.46 6.03 2.67

The samples w h i c h r e c e i v e d no d i s p e r s i o n y i e l d e d v e r y l i t t l e m a t e r i a l <4

0.

U l t r a s o n i c d i s p e r s i o n y i e l d e d b o t h s i l t and c l a y ( T a b l e 2 ) i n p r o p o r t i o n s ( y ) w h i c h a r e r e l a t e d t o t h e number f r e q u e n c y o f c l a y p e l l e t s ( x ) b y t h e l i n e a r e q u a t i o n y = 6.15 + 0.12x,

f o r w h i c h r2 = 0.68 and n

=

5.

The s h i f t i n t h e

l o c a t i o n o f t h e cumulative frequency d i s t r i b u t i o n by u l t r a s o n i c dispersion i s i l l u s t r a t e d i n F i g . 13.

QI

T h i s r e s u l t s i n changes t o c a l c u l a t e d v a l u e s o f MZ and

( T a b l e 2 ) , t h a t i s , t h e samples a p p a r e n t l y become f i n e r and more p o o r l y

s o r t e d as f i n e - g r a i n e d t a i l s a p p e a r on t h e f r e q u e n c y d i s t r i b u t i o n s .

These

r e s u l t s confirm observations i n t h i n section t h a t the pel l e t s contain q u a n t i t i e s o f c l a y and s i l t .

These f i n e s c a n n o t be d e t e c t e d i n t h e f i e l d ,

u n l e s s t h e s e d i m e n t i s hand t e x t u r e d w i t h w a t e r .

The m a t e r i a l s a r e s u b p l a s t i c ,

t h a t i s , on p h y s i c a l w o r k i n g t h e y become h e a v i e r t e x t u r e d ( B u t l e r , 1956; Dare-Edwards,

1982), a s a r e s u l t o f t h e d i s a g g r e g a t i o n o f t h e p e l l e t s .

The u l t r a s o n i c t r e a t m e n t d e s c r i b e d above does n o t r e l e a s e a l l o f t h e f i n e s from t h e c l a y p e l l e t s .

Dare-Edwards ( p e r s . comni.) exposed l u n e t t e p e l l e t s t o

much l o n g e r u l t r a s o n i c t r e a t m e n t b u t c o u l d n o t c o m p l e t e l y d i s p e r s e t h e p e l l e t s .

181

_---

100-

/-

80 SAMPLE

s

-- No -

60-

40-

0

Ultrasonically dispersed

I I

E

1

2

MI123 dispersion

3

4

+

J

I

5

6

7

8

Fig. 13. Cumulative frequency grain-size distribution for sample 23 from 230 cm at M1 (Fig. 12), showing the effects o f ultrasonic dispersion. Note that the ordinate is arithmetic and the phi scale is used for the abscissa. Therefore, it is likely that the quantities of material <4 ,0 in Table 2 do not represent the total quantity o f fines in the pellets. The results of the dispersion experiment show that a unique grain-size distribution for these sands is not attainable. However, for reasons discussed below, it seems that dry sieving yields a distribution closest to that of the sediments when they were being transported and deposited. This distribution is the most useful for the purposes of this paper. Dry sieving obviously abrades clay pellets, especially those which have begun to breakdown after deposition. However, the MZ values in Fig. 12 generally accord with qualitative observations of thin sections. That is, the finest samples, on the basis of MZ values, contain the largest quantities of small clay pellets. The quantity of pellets in crestal sands is generally < 5 % , therefore the grain-size analyses reported on the various traverses are unlikely to have been significantly affected by the presence of pellets. At M1 (Fig. 12) the hardness of the sand, as qualitatively judged by resistance to a spade, is correlated with the quantity of clay pellets. The modern cap is soft and loose, and contains <12% pellets; thereby falling into Dare-Edwards' (1982) sandy clay dune facies in which pellets make up a maximum o f 15-30% of the sediment. The remainder consists o f individual mineral grains of quartz, feldspar and other minerals. The Last Glacial sediment (210-530 cm) contains both hard and soft units, and the former have more pellets than the latter. Both fall into Dare-Edwards' clay dune facies.

182 V a l u e s o f MZ i n t h e h a r d u n i t s a r e more v a r i e d t h a n i n t h e s o f t u n i t s ( F i g . 1 2 ) , p o s s i b l y because o f d i f f e r e n t i a l breakdown o f p e l l e t s d u r i n g sieving.

However, t h i n s e c t i o n s show t h a t t h e r e i s more v a r i a t i o n i n t h e h a r d

u n i t s , w i t h dramatic v a r i a t i o n s i n t h e s i z e o f p e l l e t s . I n t h e modern cap o f l o o s e sand, t h e p e l l e t s a r e d o m i n a n t l y o f f i n e sand s i z e (2.0 t o 3.0

0), a r e

coatings (cutans).

sub-rounded,

and a f e w have v e r y t h i n o r i e n t e d c l a y

I n t h e L a s t G l a c i a l Sand t h e p e l l e t s i n t h e h a r d u n i t s a r e

commonly o f v e r y f i n e sand s i z e ( 3 . 0 t o 4.0

a),

b o t h sub-rounded and sub-

a n g u l a r , w i t h some sub-rounded f i n e sand s i z e p e l l e t s .

I n the soft units the

p e l l e t s a r e more commonly o f f i n e sand s i z e . The c l a y p e l l e t s i n t h e modern c a p o f sand a r e d i s c r e t e f e a t u r e s , w h i l e i n t h e L a s t G l a c i a l Sand t h e s m a l l p e l l e t s a r e sometimes f u s e d , and t h e r e i s a c o n s i d e r a b l e q u a n t i t y o f c l a y ' s m e a r e d ' between q u a r t z g r a i n s .

This clay i s

o f t e n w e l l o r i e n t e d b u t p e l l e t b o u n d a r i e s can b e seen i n some c a s e s .

I n the

o l d e s t u n i t i n M 1 ( b e l o w 530 cm) t h e r e a r e v e r y f e w d i s c r e t e c l a y p e l l e t s ( F i g . 1 2 ) and most c l a y o c c u r s as l i n i n g s on v o i d s and as o r i e n t e d domains between q u a r t z and f e l d s p a r g r a i n s . The same sequence o f p r o g r e s s i v e dest r u c t i o n o f c l a y p e l l e t s has been o b s e r v e d a t s i t e M3, some 11 km n o r t h w e s t o f Moomba camp, and a t L a r k ' s p i t a b o u t 10 km s o u t h o f Moomba.

Furthermore, t h e

same c o r r e l a t i o n between h a r d n e s s and p e l l e t c o n t e n t seen a t M 1 has been observed a t these two s i t e s . The breakdown o f c l a y p e l l e t s o b v i o u s l y o c c u r s a f t e r d e p o s i t i o n .

While the

d i f f e r e n c e s i n c l a y p e l l e t m o r p h o l o g y between t h e t h r e e m a j o r u n i t s r e c o g n i z e d a t M 1 a r e r e a d i l y o b s e r v a b l e , some t h i n s e c t i o n s w i t h i n t h e L a s t G l a c i a l h a r d sands show fusion.

i t t l e e v i d e n c e o f p e l l e t c o l l a p s e , w h i l e o t h e r s show e v i d e n c e o f

Da e-Edwards ( 1 9 8 2 ) made s i m i l a r o b s e r v a t i o n s i n l u n e t t e s , a r g u i n g

t h a t t h e co l a p s e o f p e l l e t s o c c u r s b y w e t t i n g and d r y i n g c y c l e s t h e a m p l i t u d e o f w h i c h i s d e t e r m i n e d b y t h e p e r m e a b i l i t y o f i n d i v i d u a l beds.

The h a r d sand

u n i t s a t M 1 a r e c l e a r l y l e s s permeable t h a n t h e s o f t sand u n i t s , and s o t h e p e l l e t s s h o u l d n o t be s t r e s s e d as o f t e n .

Dare-Edwards a l s o showed t h a t p e l l e t s

a r e b r o k e n down b y c a r b o n a t e c r y s t a l l i s a t i o n ,

b u t t h i s process i s r e l a t i v e l y

u n i m p o r t a n t i n t h e w e a k l y c a l c a r e o u s L a s t G l a c i a l dune sands o f t h e S t r z e l e c k i dunefield.

The d e g r e e o f p e l l e t breakdown i s n o t , t h e r e f o r e , a s i m p l e f u n c t i o n

o f deDth b e l o w t h e s u r f a c e .

Dune Types and Geornorphic S e t t i n g

As a l r e a d y seen, dune sand c o l o u r c o r r e l a t e s w i t h i r o n c o n t e n t i n sand g r a i n c o a t i n g s , and w i t h t h e p r e s e n c e and absence o f c l a y p e l l e t s .

The m o r p h o l o g y o f

p a l e c o l o u r e d dunes i s a l s o d i f f e r e n t f r o m t h e m o r p h o l o g y o f r e d - b r o w n dunes.

183 The red-brown dunes a r e a l m o s t everywhere s i m p l e l o n g i t u d i n a l f e a t u r e s which r e s t d i r e c t l y on e i t h e r a l l u v i u m o r bedrock and g r a v e l ( g i b b e r ) .

Over

distances o f t e n s o f k i l o m e t r e s t h e i n t e r d u n a l swales l i e a t about t h e same The dunes j o i n by means o f y - j u n c t i o n s (Mabbutt and

e l e v a t i o n ( F i g . 14a).

S u l l i v a n , 1968), and u s u a l l y b e g i n d i r e c t l y f r o m t h e i n t e r d u n a l s u r f a c e s (Fig. 1 5 ) .

I n some cases t h e y e x t e n d downwind f r o m t r a n s v e r s e dunes which

themselves l i e downwind o f e i t h e r l a k e s o r streams ( c f . Twidale, 1972; 1976).

Wasson,

Carbonate s e g r e g a t i o n s beneath t h e s u r f a c e o c c u r i n zones t h a t a r e

often up t o 1 m t h i c k , c o n s i s t o f nodules and r o o t pseudomorphs, and a p p r o x i mately p a r a l l e l t h e s u r f a c e i n c r o s s - p r o f i l e .

These s e g r e g a t i o n s a r e i n t e r -

preted as h a v i n g formed n e a r t h e ground s u r f a c e i n t h e zone o f dense p l a n t r o o t growth by pedogenic l e a c h i n g and r e - p r e c i p i t a t i o n .

They a r e t h e r e f o r e c a l -

careous p a l a e o s o l s ( c f . Churchward, 1963). The presence o f t h e s e p a l a e o s o l s shows t h a t t h e dunes a c c r e t e d v e r t i c a l l y , and a u g e r i n g w i t h i n dunes and e x a m i n a t i o n o f n a t u r a l g u l i e s has shown t h a t each u n i t o f sand between p a l a e o s o l s has an e q u i v a l e n t a t h e downwind end.

m (a.s.l.1

0.7

1.4

2.1

26

35

42

1

2

3

4

5

6

7

8 km

120

Fig. 14. C r o s s - p r o f i l e o f l o n g i t u d i n a l dunes i n t h e Simpson d u n e f i e l d . a, l o w , c l o s e l y spaced red-brown dunes. b, h i g h , w i d e l y spaced red-brown dunes. c, pale-brown dunes on a s w e l l o f sand. A l l p r o f i l e were drawn f r o m l e v e l l i n g data f o r s e i s m i c s h o t l i n e s , s u p p l i e d by D e l h i A u s t r a l i a Pty. L t d . Note t h e different v e r t i c a l exaggerations.

184

F i g . 15. Map o f r e d - b r o w n l o n g i t u d i n a l dunes f r o m t h e n o r t h e r n Simpson dunef i e l d s h o w i n g t h a t t h e dunes b e g i n f r o m t h e i n t e r d u n a l s w a l e s , r a t h e r t h a n from t r a n s v e r s e dunes o r r i v e r s . T h a t i s , each phase of a e o l i a n a c t i v i t y f o u n d e x p r e s s i o n b o t h i n v e r t i c a l a c c r e t i o n and downwind e x t e n s i o n .

The u p w i n d ends o f l o n g i t u d i n a l dunes a r e

o f t e n e r o d e d P x p o y i n g t h e maximum number o f p a l a e o s o l s w i t h i n t h e dune.

It

seems l i k e l y t h a t each t i m e a e o l i a n a c t i v i t y began, t h e p r e - e x i s t i n g dune sands were d e f l a t e d t o c o n t r i b u t e t o t h e new u n i t . The p a l e - b r o w n l o n g i t u d i n a l dunes a r e o f t e n s i m p l e f e a t u r e s w i t h i n t e r v e n i n g s w a l e s l y i n g a t a b o u t t h e same e l e v a t i o n ( F i g . 1 4 b ) .

However, more commonly

t h e p a l e l o n g i t u d i n a l dunes o c c u r i n g r o u p s , each l o n g i t u d i n a l f e a t u r e l y i n g on a l a r g e s w e l l of sand ( F i g . 1 4 c ) .

D r i l l i n g w i t h i n t h e s e s w e l l s has

d e m o n s t r a t e d t h a t t h e y c o n s i s t of a e o l i a n sand, and e x p o s u r e s w i t h i n t h e swales between t h e l o n g i t u d i n a l s show t h a t a e o l i a n a c c u m u l a t i o n has o c c u r r e d i n a l l p a r t s o f t h e s e compound f e a t u r e s (McKee, 1979).

B o t h t h e dune and t h e swale

sands c o n t a i n c l a y p e l l e t s , and c a l c a r e o u s p a l a e o s o l s . The s w e l l s commonly e x t e n d downwind, a l o n g w i t h t h e l o n g i t u d i n a l dunes, from t r a n s v e r s e dunes ( F i g . 1 6 ) w h i c h , i n t h e S t r z e l e c k i d u n e f i e l d , a r e a d j a c e n t t o f l o o d f l a t s of Cooper Creek and i t s v a r i o u s d i s t r i b u t a r i e s , and i n t h e Simpson d u n e f i e l d a r e downwind o f pans, s a l i n a s and some r i v e r c h a n n e l s .

I n both

185

dunefields the pale-brown compound dunes l i e in the topographically lowest areas, near modern streams. I n the Simpson t h i s low-lying area appears t o be the r e s u l t of t e c t o n i c movement (Krieg and Callen, 1980). I n the Strzelecki dunefield, Early T e r t i a r y Eyre Formation rocks crop o u t in the red dunes e a s t o f Strzelecki Creek a n d occur in d r i l l holes about 200 m below the surface t o the west of t h e creek, suggesting t h a t a flexure occurs along the creek. The pale-brown dunes in the S t r z e l e c k i a l s o seem t o l i e in a n area of subsidence.

B

I I

Linear dunes Transverse dune foreslopes

I-1

Waterhole

Palaeochannel

Modern channel

Spot height tm)

-

0

5krn

GN

t

Fig. 16. Dune forms a n d channel arrangements in the area j u s t n o r t h o f Moomba Camp, Strzelecki dunefield. The dated Late Pleistocene palaeochannels a r e shown in t h e southern p a r t of the map.

186 The r e d - b r o w n dunes, b y c o n t r a s t , a r e u n d e r l a i n by t h i n ( 1 - 2 m) s h e e t s o f sandy a l l u v i u m i n t h e S t r z e l e c k i d u n e f i e l d , and t h i s s e d i m e n t i s u n d e r l a i n by bedrock.

The remnants o f l o n g - d e f u n c t m e a n d e r i n g c h a n n e l s a p p e a r i n s w a l e s ,

and a r e o v e r l a i n b y dunes.

I n t e r d u n a l pans a r e a l i g n e d t r a n s v e r s e t o t h e

l o n g i t u d i n a l dunes e a s t o f S t r z e l e c k i Creek ( L o f f l e r and S u l l i v a n , 1979) and t h e s e pans p r o b a b l y r e p r e s e n t t h e remnants o f an enormous l a k e .

The

d e p o s i t i o n a l e q u i v a l e n t o f t h e l a k e i s p r o b a b l y t h e Mid-Miocene Etadunna F o r m a t i o n w h i c h l i e s a t t h e s u r f a c e i n v a r i o u s p l a c e s e a s t and s o u t h e a s t o f S t r z e l e c k i Creek, and a b o u t 150 m b e l o w t h e s u r f a c e t o t h e w e s t o f t h e f l e x u r e p o s t u l a t e d above (Wasson, i n p r e s s ) . The r e d - b r o w n dunes o f t h e n o r t h e r n Simpson d u n e f i e l d a r e u n d e r l a i n b y up t o 100 m o f sandy a l l u v i u m n e a r t h e n o r t h e r n end o f T r a v e r s e 3 ( F i g . 2 ) (Masson,

i n press).

T h i s t h i c k n e s s d e c r e a s e s t o w a r d s t h e n o r t h u n t i l e q u i v a l e n t s o f the

Etadunna F o r m a t i o n c r o p o u t i n t h e s w a l e s n e a r t h e r i v e r s d r a i n i n g f o r m t h e north.

These r i v e r s debouch between t h e dunes, b u t t h e r e i s no e v i d e n c e t h a t

t h e y r e a c h e d t h e a r e a o f p a l e dunes d u r i n g a t l e a s t t h e m o s t r e c e n t phases o f dune a c c u m u l a t i o n . I t i s c l e a r t h a t t h e c o n t r a s t i n s e d i m e n t s between t h e p a l e - b r o w n and r e d - -

brown dunes i s a l s o r e f l e c t e d i n t h e i r g e o m o r p h i c s e t t i n g .

The p a l e dunes l i e

i n a r e a s w h i c h have r e c e i v e d a l l u v i a l s e d i m e n t s b y means o f t h e l a r g e r i v e r s These r i v e r s

(Cooper Creek, D i a m a n t i n a R i v e r ) and t h e i r i m m e d i a t e a n c e s t o r s .

d r a i n t h e J u r a s s i c and C r e t a c e o u s r o c k s o f s o u t h w e s t e r n Q u e e n s l a n d ;

rocks

w h i c h a r e commonly f i n e - g r a i n e d s a n d s t o n e s , and mudstones. The r e d - d u n e s i n t h e S t r z e l e c k i d u n e f i e l d l i e o n a t e c t o n i c a l l y s t a b l e base o f C r e t a c e o u s s a n d s t o n e , E a r l y T e r t i a r y sands, and M i d - T e r t i a r y d o l o m i t i c clays.

The s t r e a m s t h a t p r e s e n t l y e n t e r t h e a r e a , and t h e i r a n c e s t o r s , d r a i n

C r e t a c e o u s r o c k s o f t h e G r e y Range t o t h e e a s t ( F i g . 1).

I n t h e south, east

o f L a k e Frome, c h a n n e l s t h a t f o r m e r l y e n t e r e d t h e d u n e f i e l d d r a i n e d t h e c r y s t a l l i n e r o c k s o f t h e s o u t h e r n B a r r i e r r a n g e and O l a r y A r c h , and t h e a r e n a c e o u s r o c k s o f t h e n o r t h e r n B a r r i e r Ranges.

I n t h e Simpson d u n e f i e l d , the

r e d - b r o w n dunes o v e r l i e a l l u v i u m t h a t was p r o b a b l y d e r i v e d f r o m t h e n o r t h , by a n c e s t o r s o f t h e H a l e , Hay and P l e n t y R i v e r s .

The m i n e r a l o g y o f t h e s e sands

s u g g e s t s a p a r t i a l s o u r c e i n t h e Archaean A r u n t a Complex ( C a r r o l l , 1944; Y e a t e s , 1 9 7 1 ) , i n a d d i t i o n t o M e s o z o i c s a n d s t o n e s and mudstones o f t h e Eromanga Basin.

I n summary, i t seems t h a t t h e r e d - b r o w n dunes have been d e r i v e d f r o m a l l u v i u m , some l a c u s t r i n e s e d i m e n t , and t h e breakdown o f b e d r o c k .

It i s l i k e l y

t h a t t h e b u l k o f t h e s e a e o l i a n sands o r i g i n a t e d as a l l u v i u m w h i c h was d e r i v e d f r o m r o c k t y p e s somewhat ( b u t n o t c o m p l e t e l y ) d i f f e r e n t f r o m t h o s e w h i c h s u p p l i e d s e d i m e n t s f o r Cooper Creek and t h e D i a m a n t i n a R i v e r .

There i s

187 evidence t h a t t h e dunes o f d i f f e r e n t c o l o u r were d e r i v e d f r o m s e d i m e n t s o f d i f f e r i n g provenance.

T h i s h y p o t h e s i s s t a n d s i n marked c o n t r a s t w i t h t h e much

discussed v i e w t h a t , i n t h e Simpson D e s e r t , dunes r e d d e n w i t h d i s t a n c e o f t r a n s p o r t downwind;

t h a t i s , t h e y r e d d e n w i t h t i m e ( W o p f n e r and T w i d a l e , 1967,

p.132;

Breed and Breed, 1979).

F o l k , 1976;

The p r o g r e s s i v e r e d d e n i n g o f

dunes away f r o m t h e i r p o s t u l a t e d s o u r c e s i s a common theme i n t h e s e d i m e n t o l o g y o f d e s e r t d u n e f i e l d s ( W a l k e r , 1979;

G a r d n e r and Pye, 1 9 8 1 ) .

I n the following

s e c t i o n o f t h i s p a p e r t h e adequacy o f t h i s h y p o t h e s i s , as a n e x p l a n a t i o n o f t h e results presented e a r l i e r , w i l l be t e s t e d . There a r e t w o k e y e l e m e n t s i n t h i s t e s t .

F i r s t l y , an e x p l a n a t i o n o f t h e

o r i g i n o f c l a y p e l l e t s and, s e c o n d l y , a n e x a m i n a t i o n o f b o t h h o r i z o n t a l and v e r t i c a l sand c o l o u r p a t t e r n s .

CLAY PELLET FORMATION Environments i n w h i c h c l a y p e l l e t s a r e b e i n g f o r m e d u n d e r p r e s e n t c o n d i t i o n s have been d e s c r i b e d i n Texas b y P r i c e ( 1 9 6 3 ) , i n n o r t h A f r i c a b y B o u l a i n e (1956), i n w e s t A f r i c a b y T r i c a r t ( 1 9 5 4 ) and i n A u s t r a l i a b y T e l l e r (1982).

et.

B o w l e r ( 1 9 7 3 ) summarized t h e common f e a t u r e s n e c e s s a r y f o r p e l l e t

formation i n t h e s e c o a s t a l l a g o o n s / m u d f l a t s and i n l a n d p a n s / l a k e s .

Seasonally

high w a t e r t a b l e s a r e r e q u i r e d i n t h e s o u r c e a r e a s , i n w h i c h f l u c t u a t i n g h i g h l y saline groundwater a l l o w s c r y s t a l l i s a t i o n o f s a l t s ( e f f l o r e s c e n c e ) w i t h i n t h e surface muds on t h e edges o f s a l t marshes, l a k e s and s a l i n e pans as e v a p o r a t i o n occurs f r o m t h e c a p i l l a r y f r i n g e ( e v a p o r a t i v e pumping).

The s a l t s m e c h a n i c a l l y

p e l l e t i s e t h e muds and w i n d t r a n s p o r t s t h e s a n d - s i z e p e l l e t s i n t o a d j a c e n t dunes,

The f i n e r p e l l e t s a r e b l o w n away as s u s p e n s i o n l o a d d u s t t o a c c u m u l a t e

a s parna ( B u t l e r , 1 9 7 4 ) . Teller

gal. (1982)

have d e s c r i b e d a modern example o f c l a y p e l l e t f o r -

mation, and a c c u m u l a t i o n o f a l o w c l a y l u n e t t e a t Pup Lagoon, a d j a c e n t t o Lake Tyrell i n northwestern V i c t o r i a .

J. Dulhunty provided t h e present author w i t h

a sample o f ' f l u f f y ' mud f r o m n e a r t h e n o r t h e r n s h o r e o f Lake E y r e N o r t h , where

the Warburton R i v e r e n t e r s t h e l a k e .

T h i s sample c o n s i s t s o f s a n d - s i z e c l a y

p e l l e t s ( F i g s . 9 and 10) w h i c h a r e b e i n g p r o d u c e d i n s m a l l q u a n t i t i e s u n d e r present c o n d i t i o n s . I n a d d i t i o n t o t h e s e c o n d i t i o n s , s t r o n g w i n d s a p p e a r t o b e n e c e s s a r y t o move pellets which e a s i l y adhere t o each o t h e r by hygroscopic a t t r a c t i o n .

Once o n a

dune, r a i n f a l l o r dew w i l l n o r m a l l y cause p e l l e t s t o a d h e r e t o one a n o t h e r . This p r o c e s s does n o t a l l o w h i g h - a n g l e b e d d i n g t o d e v e l o p , so t h a t one c h a r a c t e r i s t i c o f c l a y l u n e t t e s i s t h e i r f l a t t o low-angle bedding (Bowler,

1973).

The l o n g i t u d i n a l dunes o f t h e S t r z e l e c k i d u n e f i e l d , however, show some

high-angle b e d d i n g i n sandy c l a y u n i t s c o n t a i n i n g l e s s t h a n 30% p e l l e t s , w i t h

188

avalanche foreset laminae at 30" (Fig. 17). The clay dune facies at M1 have dips of 10-15" although some are nearly flat bedded. The ability of moderately pellet-rich sand to form avalanche laminae suggests that winds were strong and the atmosphere dry. These conditions apply especially to the Last Glacial unit.

Interbedded ripple-form I laminae and mud drapes

WeSl

Fig. 17. .Cross-stratification exposed in the east-west face of the pit at M1. For location see Fig. 8. In the Strrelecki dunefield the conditions required for clay pellet formation were met between about 23,000 and 12,000 yrs. B.P. The floodflats between the groups of dunes in the Moomba/Cooper Creek area (Fig. 16) were accumulating with muddy sand brought down Cooper Creek. Prior to this period of mud deposition, the ancestral Cooper was carrying a dominantly sandy load in large amplitude meanders, the remnants o f which can still be seen between the dunes (Fig. 16). A radiocarbon date of 22,300 f 1780 yrs. B.P. (ANU-2659) was determined on charcoal, at a site 13 km northwest of Moomba, for the transition from sand deposition to muddy sand deposition. A t the same site, the floodflat ceased to accumulate about 12,460 f 160 yrs. B.P. (ANU-2747). On the palaeochannel in Fig. 13, charcoal at the base of the muddy sand veneer, overlying the old point bar, dates to 12,020 f 150 yrs. B.P. (ANU-2862). The surface of this, the lowest part of the floodflat, is still accumulating small quantities of sediment during major floods. A more detailed account o f these dated sites is given by Wasson (in press). As seen earlier, the Last Glacial phase of dune construction ended about 13,000 yrs. B.P., approximately at the time when the deposition of the muddy veneer on the floodflats was rapidly contracting. Clay pellets can only be produced from a sediment containing mud, so the beginning of clay pellet dune

189 c o n s t r u c t i o n i s t h o u g h t t o have begun when t h e a n c e s t r a l Cooper Creek was changing f r o m a s e r i e s o f m e a n d e r i n g v i g o r o u s s t r e a m s t o a l e s s s i n u o u s m i x e d load d i s t r i b u t a r y s y s t e m a b o u t 23,000 y r s . B . P .

T h i s p e r i o d o f dune con-

s t r u c t i o n i s a p p r o x i m a t e l y t h e same as t h a t r e c o r d e d i n The M a l l e e o f New S o u t h Wales and V i c t o r i a b y B o w l e r ( 1 9 7 8 ) , and i n o t h e r m i d - l a t i t u d e d e s e r t s (Sarnthein, 1978). I n t h i s model, t h e c l a y p e l l e t s and q u a r t z o s e sands w h i c h f o r m t h e dunes o f the S t r z e l e c k i d u n e f i e l d were d e r i v e d b y d e f l a t i o n f r o m c o n t e m p o r a n e o u s l y deposited s e d i m e n t s on t h e f l o o d f l a t s .

The s a l i n e g r o u n d w a t e r was m a i n t a i n e d

by s u r f a c e f l o w , b u t s e a s o n a l a n d / o r l o n g e r - t e r m f l u c t u a t i o n s o f t h e w a t e r table p r o d u c e d t h e n e c e s s a r y c o n d i t i o n s f o r p e l l e t i s a t i o n .

The s a l i n e w a t e r

with m o n t m o r i l l o n i t i c c l a y s may have a i d e d p e l l e t i s a t i o n b y means o f f l o c c u lation.

S t r o n g w i n d s c a r r i e d o u t t h e d e f l a t i o n , and t h e s a l i n i s e d f l o o d f l a t s

were n o t e n c o u r a g i n g t o v e g e t a t i o n . These c o n d i t i o n s o b v i o u s l y n o l o n g e r p r e v a i l .

Surface waters a r e f r e s h ,

supporting a C o n c h o s t r a c a n f a u n a i n i n t e r d u n a l s w a l e s (De D e c c k e r , p e r s .

comm.).

The modern s t a t i c w a t e r t a b l e l i e s a b o u t 40 m b e l o w t h e s u r f a c e i n t h e

Moomba a r e a , and t h e g r o u n d w a t e r i s h i g h l y s a l i n e .

The L a t e H o l o c e n e sand

which caps most p a l e dunes i n t h e S t r z e l e c k i d u n e f i e l d i s l a r g e l y r e w o r k e d f r o m the o l d e r p a r t s o f t h e dunes.

This i s demonstrated by t h e l a c k o f small c l a y

p e l l e t s , and t h e g e n e r a l roundness o f t h e p e l l e t s i n t h e m o b i l e caps.

The

upwind ends o f t h e s e dunes a r e commonly d e f l a t e d , t h e sand m o v i n g down-dune. The contemporaneous d e p o s i t i o n o f a l l u v i u m and f o r m a t i o n of dunes, i n t h e S t r z e l e c k i d u n e f i e l d w e s t o f S t r z e l e c k i Creek, may a l s o have o c c u r r e d i n t h e Simpson d u n e f i e l d n e a r t h e modern c h a n n e l s .

But i t i s clear that the controls

on d e f l a t i o n and dune f o r m a t i o n n o r t h o f K a l l a k o o p a h Creek, i n t h e v i c i n i t y o f

the pans, were r a t h e r d i f f e r e n t .

The pans more t h a n 20 km n o r t h o f t h e

Kallakoopah have n o t been c o n n e c t e d t o t h e c r e e k d u r i n g a t l e a s t t h e l a s t period o f dune c o n s t r u c t i o n , f o r t h e r e i s n o e v i d e n c e o f e i t h e r y o u n g a l l u v i u m or palaeochannels between t h e dunes.

The pans a r e c u t i n sandy a l l u v i u m w h i c h

l i e s i m m e d i a t e l y b e n e a t h t h e dunes and o v e r l i e s l a c u s t r i n e and a l l u v i a l sediments.

E x p o s u r e a r o u n d t h e pans a r e o f t e n good, and s t r a t i g r a p h i c

relationships can be observed. The pans have v e r y s m a l l c a t c h m e n t s , and t h e y a r e o b v i o u s l y c r e a t e d and enlarged b y d e f l a t i o n . formation,

To p r o d u c e t h e n e c e s s a r y c o n d i t i o n s f o r c l a y p e l l e t

i t must b e presumed t h a t t h i s d e f l a t i o n was g r o u n d w a t e r c o n t r o l l e d .

Oisplacive gypsum c r y s t a l s w i t h i n dune sand h i g h above t h e pans p r o v i d e s

A t present t h e s t a t i c groundwater t a b l e i s some 20 m b e l o w t h e pans i n t h e a r e a 50-100 km n o r t h o f K a l l a k o o p a h Creek o n

evidence o f g r o u n d w a t e r f l u c t u a t i o n s .

Traverse 3 and d e f l a t i o n f r o m t h e pans i s v e r y l i m i t e d .

190 The absence o f c l a y p e l l e t s i n t h e r e d - b r o w n dunes and t h e g e o m o r p h i c s e t t i n g o f t b e s e dunes shows t h a t t h e c o n d i t i o n s f o r p a l e dune f o r m a t i o n and r e d dune f o r m a t i o n were v e r y d i f f e r e n t .

The m o b i l i z a t i o n o f sand f o r t h e p a l e

dunes i n v o l v e d g r o u n d w a t e r , w h i l e m o b i l i z a t i o n f o r f o r m a t i o n o f t h e r e d dunes presumably r e q u i r e d l o w values o f t h e aerodynamic roughness l e n g t h , f r e q u e n t d r y i n g o f t h e s e d i m e n t s b e i n g d e f l a t e d , a n d / o r enhanced w i n d i n e s s (Ash and Wasson, i n p r e s s ) .

The r e d brown dunes were f o r m e d b y d e f l a t i o n o f s e d i m e n t

l y i n g i n s l i g h t l y e l e v a t e d a r e a s where g r o u n d w a t e r p r o b a b l y d i d n o t r e a c h t h e i n t e r d u n a l swales.

As n o t e d e a r l i e r , t h e r e d - b r o w n dunes commonly b e g i n f r o m

t h e s u r f a c e u p o n w h i c h t h e y r e s t , r a t h e r t h a n e x t e n d i n g downwind f r o m t r a n s v e r s e dunes.

T h e r e f o r e , t h e s o u r c e o f t h e sands i s c l o s e t o t h e dunes, n o t

hundreds o f k i l o m e t r e s upwind. The age o f t h e p a l e dunes o f t h e S t r z e l e c k i d u n e f i e l d i s r e a s o n a b l y w e l l known, a t l e a s t a t a f e w s i t e s , b u t t h e r e i s no c o m p a r a b l e c h r o n o l o g i c a l control

on t h e r e d - b r o w n dunes.

The n o n - c a l c a r e o u s caps o f w e l l - b e d d e d r e d -

brown sand c o n t a i n b a c k e d b l a d e s , s m a l l s t o n e t o o l s made o n l y d u r i n g t h e l a s t 4,000 y r s . ( P . Hughes, p e r s . comm.).

B e n e a t h t h i s p e r i o d i c a l l y m o b i l e cap

t h e r e i s a c a l c a r e o u s p a l a e o s o l w h i c h gave an a p p a r e n t I 4 C age o f 15,900 t 320 y r s . B.P.

(ANU-2280) a t a s i t e i n f a r n o r t h w e s t e r n N.S.W.

( F i g . 1).

I t seems

t h a t t h e m o b i l e c a p i s o f L a t e H o l o c e n e age w h i l e t h e 16,000 y r p a l a e o s o l t o p s t h e L a s t G l a c i a l sand.

T h e r e a r e p r e - L a s t G l a c i a l u n i t s as w e l l .

This i s a

s p e c u l a t i v e c h r o n o l o g y and r e q u i r e s e x t e n s i v e t e s t i n g . W h i l e i t i s n o t c l e a r i f t h e r e d - b r o w n and p a l e - b r o w n dunes a r e o f t h e same age, i t i s l i k e l y t h a t t h e enhanced w i n d i n e s s p o s t u l a t e d f o r c l a y p e l l e t movement a l s o m o b i l i s e d sand i n t h e a r e a s o f r e d dunes (Ash and Wasson, i n press).

I t i s a r e a s o n a b l e w o r k i n g h y p o t h e s i s t h a t t h e dunes a r e o f t h e same

age b u t t h e p r o c e s s e s o f t h e i r f o r m a t i o n a r e v e r y d i f f e r e n t . The s i m p l e scheme o f p r o g r e s s i v e a g e i n g o f dune sand away f r o m s o u r c e a r e a s does n o t t a k e a c c o u n t o f t h e v e r y d i f f e r e n t p r o c e s s e s o p e r a t i n g i n a r e a s o f d i f f e r e n t sand c o l o u r .

F u r t h e r m o r e , i t does n o t t a k e a c c o u n t o f m u l t i p l e

s o u r c e s f o r dune sands, b u t p o s t u l a t e s t h a t a l l dune sand o r i g i n a t e d n e a r Lake E y r e i n t h e Simpson d u n e f i e l d , f o r example.

As a l r e a d y seen, t h e g r a i n - s i z e

data suggest t h a t t h i s p o s t u l a t e i s i n c o r r e c t .

COLOUR PATTERNS The e x p l a n a t i o n o f t h e s p a t i a l ( o r h o r i z o n t a l ) p a t t e r n s o f sand c o l o u r ( F i g . Z ) , as t h e r e s u l t o f p r o g r e s s i v e r e d d e n i n g downwind, f a i l s d r a m a t i c a l l y i n one i m p o r t a n t a r e a .

The r e d - b r o w n dunes t o t h e e a s t o f S t r z e l e c k i Creek are

a d j a c e n t t o p a l e dunes on, and t o t h e n o r t h o f , T r a v e r s e 2.

It i s impossible

t o e x p l a i n t h i s b o u n d a r y as t h e r e s u l t o f d i f f e r e n t r a t e s o f r e d d e n i n g , away

191 from source a r e a s , o n e i t h e r s i d e o f t h e c r e e k , because t h e p a l e dunes t o t h e west o f t h e c r e e k do n o t r e d d e n downwind, The v e r t i c a l p a t t e r n s o f c o l o u r i n red-brown sand, d e t e r m i n e d b y a u g e r i n g , and seen a t a number o f s e c t i o n s seen t h r o u g h dunes, show u n e q u i v o c a l l y t h a t the dunes a r e r e d t h r o u g h o u t .

The c o a t i n g s on t h e g r a i n s c o n s i s t o f i r o n and

clay l y i n g i n h o l l o w s o r p i t s on t h e g r a i n s , p r o t e c t e d f r o m a b r a s i o n ( c f . F o l k ,

1976).

The dune sands a p p e a r t o have been d e r i v e d f r o m a ' p r e - r e d d e n e d '

sediment, j u s t l i k e t h a t w h i c h l i e s b e n e a t h b o t h t h e dunes and i n t e r d u n a l swales.

Pedogenesis w i t h i n a l l u v i u m , and s e d i m e n t s o f o t h e r o r i g i n s , has

coated t h e g r a i n s w i t h i r o n and c l a y , and t h e s e c o a t i n g s have been a b r a d e d during a e o l i a n t r a n s p o r t .

I f t h e dunes had c o n s i s t e d o f p a l e brown sands w h i c h

were reddened i n s i t u , t h e n t h e r e d d e n i n g s h o u l d d e c r e a s e b e l o w t h e s u r f a c e . This i s p r e c i s e l y t h e p a t t e r n t h a t i s f o u n d i n t h e p a l e dunes o f b o t h d u n e f i e l d s , where t h e o l d e s t p a l a e o s o l s a r e s l i g h t l y r u b i f i e d ( 7 . 5 Y R 7 / 4 ) . Some o f t h e s e o b j e c t i o n s t o t h e downwind r e d d e n i n g h y p o t h e s i s p o s s i b l y c a n be c o u n t e r e d b y s u g g e s t i n g t h a t t h e s e dunes t u r n o v e r w i t h t i m e t h e r e b y producing u n i f o r m l y r e d sand f r o m t o p t o b o t t o m .

However, t h e e v i d e n c e o f

palaeosols s e p a r a t i n g b o d i e s o f sand i n v e r t i c a l e x p o s u r e s s u g g e s t s t h a t , w h i l e some downwind movement o b v i o u s l y o c c u r s , t h e dunes do n o t m i g r a t e v e r y f a r during each i n t e r v a l o f a e o l i a n a c t i v i t y . v e r t i c a l g r o w t h o f t h e s e dunes.

T h e r e i s abundant e v i d e n c e f o r t h e

I t must be c o n c l u d e d t h a t a s p e c t s o f t h e

colour p a t t e r n s d o n o t s u p p o r t t h e downwind r e d d e n i n g h y p o t h e s i s , b u t a c t u a l l y counter t h e h y p o t h e s i s . How t h e n can we e x p l a i n t h e p a t t e r n o f sand c o l o u r s a t C u r d l a w i d n y Lagoon (Fig. 6 ) and o t h e r c a s e s o f a s i m i l a r k i n d n o t documented i n t h i s p a p e r ?

Sand

t h a t e n t e r s l a k e s , e i t h e r b y w i n d o r w a t e r t r a n s p o r t a t i o n , t e n d s t o l o s e some o f i t s i r o n l c l a y c o a t i n g d u r i n g wave t r a n s p o r t .

T h i s i s c l e a r l y seen a t

Curdlawidny w h e r e r e d - b r o w n dunes s u p p l y s a n d t o t h e l a k e on t h e w e s t e r n s i d e but t h e dunes o n t h e e a s t e r n (downwind) s h o r e a r e p a l e .

It i s proposed t h a t

f u r t h e r downwind t h e p a l e sands m i x w i t h r e d - b r o w n sands d e r i v e d f r o m o l d e r material which surround t h e lake.

T h i s m i x i n g o f sands o f d i f f e r e n t s o u r c e s

(on a meso t o m i c r o s c a l e ) can b e seen e a s i l y i n t h e f i e l d w i t h a hand l e n s . As a g e n e r a l p r o p o s i t i o n i t i s s u g g e s t e d t h a t downwind r e d d e n i n g o f dunes may r e f l e c t downwind r e d d e n i n g ( a n d a g e i n g ) o f t h e s o u r c e s o f dune sands.

In

the S i m p s o n - S t r z e l e c k i d u n e f i e l d t h e r e d s e d i m e n t s , f r o m w h i c h r e d dunes have been d e r i v e d , a r e p r o b a b l y o l d e r t h a n t h e p a l e a l l u v i u m f r o m w h i c h t h e p a l e dunes have f o r m e d .

T h i s p r o p o s i t i o n may a l s o a p p l y t o t h e w e l l documented

downwind r e d d e n i n g i n w e s t e r n L i b y a ( W a l k e r , 1 9 7 9 ) .

192 CONCLUSION One o f t h e m o s t o b v i o u s f e a t u r e s o f t h e dunes o f t h e S i m p s o n - S t r z e l e c k i dunefield i s t h e i r colour.

Dune c o l o u r s h a v e been mapped and t h e sands and

dunes examined w i t h i n each o f t h e m a j o r c o l o u r r e g i o n s .

T h r e e t r a v e r s e s were

l a i d o u t t o c r o s s examples o f b o u n d a r i e s between t h e s e r e g i o n s , and a s p e c t s o f m i n e r a l o g y , i r o n c o n t e n t and g r a i n - s i z e examined.

The b o u n d a r i e s a c t u a l l y

c o n s i s t o f t r a n s i t i o n a l zones, b u t t h e s e zones a r e q u i t e n a r r o w i n some c a s e s . T h e r e f o r e t w o p r i m a r y c o l o u r s can be d i s t i n g u i s h e d :

p a l e brown and red-brown.

I n t w o o u t o f t h r e e t r a v e r s e s , t h e r e d - b r o w n dunes have l o w e r heavy m i n e r a l I n both

c o n t e n t s t h a n t h e p a l e brown dunes, t h e e x c e p t i o n b e i n g T r a v e r s e 3.

T r a v e r s e 1 and 2 t o t a l f e l d s p a r c o n t e n t i s l o w e r i n t h e r e d - b r o w n t h a n i n t h e p a l e brown dunes.

I n b o t h T r a v e r s e 2 and 3 t o t a l i r o n c o n t e n t i s h i g h e r i n t h e

r e d - b r o w n dunes t h a n i n t h e p a l e brown dunes.

O f these three variables, only

i r o n c o n t e n t i s l i k e l y t o a f f e c t sand c o l o u r , and so a n o t h e r a r e a was sampled n e a r C u r d l a w i d n y Lagoon i n t h e P a r a k y l i a d u n e f i e l d .

Total i r o n content i s

a g a i n h i g h e r i n t h e r e d - b r o w n dunes. While i t appears t h a t t h e c o l o u r d i f f e r e n c e s can be accounted f o r b y differences i n i r o n content, importance.

t h e t h i c k n e s s o f g r a i n c o a t i n g s i s a l s o o f some

That i s , c o a t i n g s a r e t h i c k e s t on t h e reddest g r a i n s .

The o t h e r

c h a r a c t e r i s t i c s n o t e d o n t h e t r a v e r s e s ( f e l d s p a r and h e a v y m i n e r a l c o n t e n t ) s i m p l y r e f l e c t d i f f e r e n c e s i n t h e source sediments.

This interpretation i s

s u p p o r t e d b y t h e q u a n t i t a t i v e d i f f e r e n c e s i n m i n e r a l o g y between a r e a s o f d i f f e r i n g sand c o l o u r . There i s no c l e a r s e p a r a t i o n on an M Q parts o f the dunefields.

Z I

d i a g r a m o f c r e s t a l sands i n v a r i o u s

However, t h e r e i s a t e n d e n c y f o r t h e f i n e s t ( a n d

p a l e s t ) sands t o o c c u r n e a r t h e modern c h a n n e l s o f Cooper Creek, t h e D i a m a n t i n a R i v e r , and K a l l a k o o p a h Creek. red-brown,

The c o a r s e r c r e s t a l sands a r e g e n e r a l l y

and l i e away f r o m t h e s e c h a n n e l s .

T h i s t r e n d cannot be e a s i l y

i n t e r p r e t e d b y t h e n o t i o n t h a t a l l o f t h e dune sand o r i g i n a t e d i n t h e modern c h a n n e l s. E x a m i n a t i o n o f b o t h p a l e brown and r e d - b r o w n dune sand i n t h i n s e c t i o n has d e m o n s t r a t e d q u i t e c l e a r l y t h a t t h e f o r m e r c o n t a i n o f t e n l a r g e q u a n t i t i e s of c l a y p e l l e t s w h i l e t h e l a t t e r c o n t a i n none. w i t h those found i n c l a y lunettes. p e l l e t formation,

The c l a y p e l l e t s a r e i d e n t i c a l

By r e f e r e n c e t o modern examples o f c l a y

i t has been p o s s i b l e t o s p e c i f y t h e c o n d i t i o n s w h i c h p r e -

v a i l e d between 23,000 and 13,000 y r s ago when t h e y w e r e a c t i v e l y b e i n g produced.

S a l i n e g r o u n d w a t e r , w h i c h i s now t e n s o f m e t r e s b e l o w t h e s u r f a c e ,

i n t e r s e c t e d t h e surface possibly seasonally.

Drying allowed s a l t s t o

c r y s t a l l i z e i n t h e sandy muds, s u p p l i e d i n t h e c a s e o f t h e S t r z e l e c k i d u n e f i e l d b y Cooper Creek, t h e r e b y p e l l e t i s i n g t h e s e d i m e n t s .

I n t h e Simpson d u n e f i e l d

193 old alluvium was p e l l e t i s e d by groundwater f uctuation, b u t contemporaneous alluvial deposition and d e f l a t i o n was probab y limited t o the floodplains of Kallakoopah Creek a n d t h e Diamantina River. Falling water-tables, reduced a l l u v i a t i o n , a n d possibly decreased windiness around 13,000 stopped pale dune construction. Unfortunately the age of the red-brown dunes i s not well enough known t o say i f they became s t a b l e a t the same time. A Late Holocene phase of re-working appears t o have affected both pale and red-brown dunes. The formation of t h e pale dunes required p a r t i c u l a r hydrologic conditions, while the red-brown dunes could have been formed under any climatic conditions which limited vegetation cover and maintained strong winds. The differences in geomorphic s e t t i n g of the two groups of dunes shows t h a t there i s no simple gradation from one t o the other. This in turn suggests t h a t explanation of the downwind reddening of dunes, seen e s p e c i a l l y in the Simpson dunefield, i s n o t simply a function of ageing of the iron minerals in grain coatings. The progressive ageing hypothesis a l s o does not account f o r the l i k e l y multiple sources of sediment f o r dune construction. The hypothesis a l s o f a i l s t o account f o r e i t h e r complete reddening of red-brown dunes, or t h e boundary between pale a n d red-brown dunes e i t h e r side of the NNE-SSW trending Strzelecki Creek. I t i s concluded t h a t reddening of dune sand in the Simpson-Strzelecki dunefield largely occurred p r i o r t o dune construction. The red-brown dunes a r e b u i l t of pre-reddened sediments while the pale dunes a r e b u i l t of pale sediments. Both bodies of sediment were derived from d i f f e r e n t sources, so t h a t dune colour ultimately r e f l e c t s source sediment provenance. This paper gives the f i r s t account of a vary l a r g e f i e l d (some 100,000 kmL) of longitudinal d e s e r t dunes rich in clay p e l l e t s . The palaeohydrological conditions proposed t o explain t h e i r formation appears t o be r a t h e r d i f f e r e n t from the hot waterless environment normally associated with d e s e r t dune formation. The presence o f water in swales with a seasonally warm t o hot atmosphere combines environmental f a c t o r s no longer found in Australia.

The

h i g h groundwater level was probably t h e r e s u l t of a long period of positive water balance preceding 25,000 y r s B.P. (Bowler, 1978) r a t h e r t h a n a s t a t e in equilibrium with conditions a t the peak of the Last Glacial. These

relationships show t h a t a simple uniformitarian model f o r the i d e n t i f i c a t i o n of aeolian deposits in the rock record i s l i k e l y t o be unsuccessful. A more fruitful approach i s t o i n v e s t i g a t e t h e evolution of 'modern' sediments through

at l e a s t t h e Late Quaternary.

194 ACKNOWLEDGMENTS

I n t h e l a b o r a t o r y Mr Jim Caldwell performed a n a l y s e s w i t h s k i l l , w h i l e in t h e f i e l d K . Q u a y l e and M. Campion provided c o n s i d e r a b l e a s s i s t a n c e . J.N. J e n n i n g s and R . W . Galloway read t h e m a n u s c r i p t and made h e l p f u l comments. F i n a l l y , J.M. Bowler c o n t r i b u t e d t o the i d e a s i n t h i s paper d u r i n g many conversations. FIEFE R E N C E S

Cish, J.E. and Wasson, R.J., in p r e s s . Vegetation and sand m o b i l i t y i n t h e A u s t r a l i a n d e s e r t d u n e f i e l d . Z e i t . Geomorphol. N . F . , Suppl. Bd. E o u l a i n e , J . , 1956. Les l u n e t t e s des b a s s e s p l a i n e s o r a n a i s e s ; f o r m a t i o n e o l i e n n e a r g i l e u s e s l i e s a l ' e x t e n s i o n des s o l s s a l i n s ; La Sebkha de Ben Ziane; l a d e p r e s s i o n de C h a n t r i t : Proc. Conf. I n t . Assoc. Quaternary Res., 4 t h , pp.143-150. Eowler, J.M., 1973. Clay dunes: t h e i r o c c u r r e n c e , formation and e n v i r o n mental s i g n i f i c a n c e . E a r t h - S c i e n c e Reviews, 9: 315-338. Bowler, J.M., 1978. G l a c i a l age e v e n t s a t high and low l a t i t u d e s : a s o u t h e r n hemisphere p e r s p e c t i v e . I n : E . M . v a n Zinderen Bakker ( E d i t o r ) , A n t a r c t i c G l a c i a l H i s t o r y and World Palaeoenvironrnents. A . A . Balkema, Rotterdam, pp.149-172. F r e e d , C.S. and Breed, W.J., 1979. Dunes and o t h e r windforms of c e n t r a l A u s t r a l i a ( a n d a comparison with l i n e a r dunes on t h e Moenkopi P l a t e a u , A r i z o n a ) . I n : Farouk El-Baz and D.M. Warner ( E d i t o r s ) , Apollo-Soyuz T e s t P r o j e c t Summary S c i e n c e R e p o r t , V . 2 , Earth O b s e r v a t i o n s and Photography. U.S. National A e r o n a u t i c s and Space A d m i n i s t r a t i o n SP-412, pp.319-358. B u t l e r , B . E . , 1956. P a r n a , an a e o l i a n c l a y . Aust. J . S c i . , 18: 145-151. E u t l e r , B . E . , 1974. A c o n t r i b u t i o n towards t h e b e t t e r s p e c i f i c a t i o n of parna a n d some o t h e r a e o l i a n c l a y s i n A u s t r a l i a . Z e i t . Geomorphol. N . F . , Suppl. Bd., 20: 106-116. C a r r o l l , D . , 1944. The Simpson D e s e r t E x p e d i t i o n , 1939. S c i e n t i f i c r e p o r t s : No. 2 , Geology - d e s e r t s a n d s . T r a n s . R . S O C . S . Aust., 68: 49-59. Churchward, H . M . , 1963. S o i l s t u d i e s a t Swan H i l l , V i c t o r i a , A u s t r a l i a , IV: Ground-surface h i s t o r y and i t s e x p r e s s i o n i n t h e a r r a y of s o i l s . Aust. J . S o i l Res., 1: 242-255. Dare-Edwards, A . J . , 1979. L a t e Q u a t e r n a r y s o i l s on c l a y dunes of t h e Willandra Lakes, New South Wales. PhD t h e s i s , Aust. Nat. U n i v . , Canberra. Dare-Edwards, A . J . , 1982. Clay p e l l e t s of c l a y dunes: t y p e s , mineralogy, o r i g i n and e f f e c t o f p e d o g e n e s i s . In: R.J. Wasson ( E d i t o r ) , Q u a t e r n a r y Dust Mantles o f China, New Zealand and A u s t r a l i a . Aust. N a t . Univ. Folk, R . L . , 1968. P e t r o l o g y of Sedimentary Rocks. A u s t i n , Texas. H e m p h i l l ' s 170pp. Folk, R . L . , 1976. Reddening of d e s e r t s a n d s : Simpson D e s e r t , N.T., A u s t r a l i a . J . Sediment. P e t r o l . , 46: 604-615. Gardner, R . and Pye, K . , 1981. N a t u r e , o r i g i n and palaeoenvironmental s i g n i f i c a n c e o f red c o a s t a l and d e s e r t dune s a n d s . Prog. Phys. Geogr. 5 : 514-534. Krieg, G.W. and C a l l e n , R . A . , 1980. Geological o b s e r v a t i o n s i n the playa r e g i o n of t h e Simpson D e s e r t , South A u s t r a l i a . Dept. Mines and Energy .. South A u s t r a l i a , Report Book No. 80/68. L o f f l e r , E . and S u l l i v a n , M . E . , 1979. Lake D i e r i r e s u r r e c t e d : an i n t e r p r e t a t i o n u s i n g s a t e l l i t e imagery. Z e i t . Geomorphol., 23: 233-242. Mabbutt, J.A. and S u l l i v a n , M.E., 1968. The f o r m a t i o n of l o n g i t u d i n a l dunes: e v i d e n c e from t h e Simpson D e s e r t . Aust. Geogr., 10: 483-487. McKee, E . D . ( E d . ) , 1979. A Study o f Global Sand S e a s . U.S. Geol. S u r v . , P r o f . P a p . 1052, 42913.

195 P r i c e , W.A., 1963. Physicochemical and environmental f a c t o r s i n c l a y dune genesis. J. Sediment. P e t r o l . , 33: 766-778. Rhodes, E.G., 1980. Modes o f Holocene c o a s t a l p r o g r a d a t i o n , G u l f o f C a r p e n t a r i a . PhD t h e s i s , Aust. Nat. U n i v . Canberra. Sarnthein, M., 1978. Sand d e s e r t s d u r i n g g l a c i a l maximum and c l i m a t i c optimum. Nature, 272: 43-44. T e l l e r , J.T., Bowler, J.M. and Macumber, P.G., 1982. Modern s e d i m e n t a t i o n and hydrology i n Lake T y r r e l l , V i c t o r i a . J. Geol. SOC. A u s t . , v . 29, p.159-176. T r i c a r t , J., 1954. I n f l u e n c e des s o l s s a l e s s u r l a d e f l a t i o n e o l i e n n e en basse M a u r i t a n i e e t dans l a D e l t a du Senegal. Rev. Geomorphol. Dyn., 5 : 124-132. 1972. E v o l u t i o n o f sand dunes i n t h e Simpson D e s e r t , c e n t r a l Twidale, C.R., A u s t r a l i a . I n s t . B r i t i s h Geographers T r a n s a c t i o n , Publ. No. 56, pp.77-109. Walker, T.R., 1979. Red c o l o r i n dune sand. I n : E.D. McKee ( E d i t o r ) , A Study of Global Sand Seas. U.S. Geol. Surv., P r o f . Pap. 1052, pp.61-82. 1976. Holocene a e o l i a n landforms i n t h e Belarabon area, S.W. o f Wasson, R.J., J . and Proc. R. SOC. N.S.W., 109: 91-101. Cobar, N.S.W. Wasson, R.J., i n press. The C a i n o z o i c h i s t o r y o f t h e S t r z e l e c k i and Simpson d u n e f i e l d s ( A u s t r a l i a ) , and t h e o r i g i n o f t h e d e s e r t dunes. Z . Geomorph. Suppl , Bd. 1967. Geomorphological h i s t o r y o f t h e Lake Wopfner, H. and Twidale, C.R., Eyre Basin. I n : J.N. Jennings and J.A. Mabbutt ( E d i t o r s ) , Landform S t u d i e s from A u s t r a l i a and New Guinea. A u s t . Nat. Univ. Press, Canberra, Aust., pp. 118-143. 1971. S h a l l o w s t r a t i g r a p h i c d r i l l i n g , western Eromanga B a s i n and Yeates, A.N., Alcoota sheet area, N o r t h e r n T e r r i t o r y , 1971. Bureau o f M i n e r a l Resources, Geology and Geophysics, Record 1971/120. Appendix

ANALYTICAL METHODS.

1. Standard c l a y - s i z e m i n e r a i i d e n t i f i g a t i o n by XRD was c a r r i e d o u t u s i n g CUKU r a d i a t i o n , h e a t i n g a t 450 C and 550 C, and g l y c o l a t i o n . 2. Sand c o l o u r s were determined on samples b r o u g h t from t h e dunes t o t h e l a b oratory, n o t i n t h e f i e l d . C o l o u r s were t h e n determined under u n i f o r m l i g h t i n g on a i r - d r y samples. S i z i n g was n o t done b e f o r e c o l o u r d e t e r m i n a t i o n . The Standard Japanese C o l o u r Code was used.

3. Heavy m i n e r a l s were separated u s i n g bromoform, and t h e s e p a r a t e s ground f o r XRD a n a l y s i s . 4. T o t a l i r o n was d e t e r m i n e d c o l o r i m e t r i c a l l y a f t e r n i o i s t e n i n g w i t h 6N HC1 and complexing w i t h KCNS. F e r r i c i r o n was determined i n t h e same way, w i t h t h e a d d i t ion o f a s t e p i n v o l v i n g a p r o t e c t i v e c o v e r o f e t h y l e t h e r f o r 24 hours. F e r r o u s i r o n can be c a l c u l a t e d as t h e d i f f e r e n c e between t o t a l i r o n and f e r r i c i r o n .

5. CaC03 was determined by v o l u m e t r i c c a l c i m e t e r , iiieasuring C02 volume. 6. Carbon i n g r a i n c o a t i n g s was d e t e r m i n e d by p h y s i c a l removal o f t h e c o a t i n g s , then o x i d a t i o n i n a f u r n a c e and d i r e c t iiieasureiiient o f CO a f t e r s c r u b b i n g t o remove s u l p h u r , o x i d e s o f n i t r o g e n , e t c . T h i s method a l l h s d e t e r m i n a t i o n o f as l i t t l e as 1 0 ppm. carbon.

7 . G r a i n s f o r EDAX were mounted i n a r a l d i t e t h e n ground and f i n i s h e d w i t h

0.5

pm

diamond l a p .

8. U l t r a s o n i c d i s p e r s i o n was performed by a probe r u n a t 20,000 c y c l e s / m i n u t e f o r 10 m i n u t e s i n a m i x t u r e o f 100 m l d i s t i l l e d water, 5 m l o f 5% c a u s t i c soda and 10 m l o f 10% t r i - p o l y - p h o s p h a t e .