; directional 
Minor 
directions 
I-NNE 
:ne 
I-NNE 
INE; ENE; ESE 
Chott el 
is should reflect 
he folding of 
■nstructed 
suggests that 
mt during 
■ata of the 
iuld probably 
lei to the 
'he present-day 
Fedjadj is 
iral association 
ch would fit 
'his can partly 
the Chott el 
is a result of 
1 axis which 
;ediments in 
Undoubtedly 
ihin the 
tensional 
'old where the 
i in the deeper 
d axes probably 
dominant 
mds in the area, 
under 
iry strata, 
lie fold axes 
:icularly the 
s likely 
.gnments relate 
¡en aquifers 
its. The strata 
for the extent 
ii-west Chott 
iat it is found 
it and that there 
c d 
Figure 4. Band 3 images (cf. Fig.3) after directional filtering: a) North b)North-West c) West d) South-West 
s orthogonal to 
>wn physical 
patterns related 
terials 
ictions (Park, 
: case in this 
lary lineament 
:rms of the 
dine. There is 
.long the 
the resistant 
iber of cuestas, 
baga, display 
.ted 
.rallel to the 
. These can be 
ts on the 
the hypothesised 
.ya sediments. 
5.2. Aioun distribution and structural control 
It is not possible to determine alignment directions 
of aioun in the central Chott el Djerid. This was 
because of the lower number of aioun when compared to 
spring mounds. However the entire aioun field appears 
as a large lineament orientated NNE-SSW. 
If aioun are related to deep groundwater upwelling 
it should be possible to relate the orientation of 
the aioun field to the Alpine structural trends in 
the region. If there is little relationship between 
them then it might suggest that aioun are controlled 
by shallow, rather than deep, groundwater movements. 
The evidence relating the aioun field orientation to 
structural trends is at the present time somewhat 
circumstantial. The aioun field appears to be located 
at the end of the Chott el Fedjadj anticline. This 
anticline plunges to the west and is overlain totally 
by playa sediments of the Chott el Djerid about 8km 
before the eastern edge of the aioun field. 
Geological strata in the Djebel el Asker, to the 
north of the Chott el Djerid, curve southwards in 
the direction of the aioun field (Fig. 2) . If the 
southerly structural trend of the Djebel el Asker 
rocks is continued the aioun field falls along its 
course. Appealing though this relationship may 
appear it still does not explain why there is deep 
groundwater coming up to the surface along this trend 
line. It may be that the entire structure is 
related to the buried nose of the Chott el Fedjadj 
anticline but without an adequate sub-playa 
reconstruction this can only be a matter of 
conjecture at the present time. 
6. CONCLUSIONS 
It has been shown that the detection of spring mounds 
and aioun on playas from remotely sensed imagery has 
many advantages over conventional ground survey both 
in terms of overcoming logistical and geomorphological 
aspects; and that it enables advantage to be taken 
of the shape and spectral characteristics of these 
features. A further major advantage of mapping the 
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