Geology Reference
In-Depth Information
(b)
Figure 7.19.
(b) Northern Flinders Ranges, South Australia (Publicity and Tourist Bureau, South Australia).
Figure 7.20.
Faceted slopes in granite in northwest Queensland (CSIRO).
The topography appears to evolve by stream dissection of massifs in which sheet structure is
poorly developed or absent, or in regions in which weathering has eliminated, or all but destroyed,
structural influence of the country rock. The landform assemblage can be explained by considering
the sequence of events following the stream dissection of a duricrusted surface. The sidewalls of
the valley consist of faceted slopes (Fig. 7.20); the bluff in some areas being coincident with a
duricrust capping (Figs 1.1h, 4.12 and 7.20). Examples of faceted granitic slopes associated with
duricrusts are commonplace, but the duricrust is not essential to their formation. Such faceted
slopes are maintained for some time, but because of the basal sapping of the bluff the latter is grad-
ually reduced from below, until it is eliminated. The slopes then consist of essentially rectilinear
debris facets (bedrock but with a veneer of detritus). They intersect in sharp crests or aretes: all
slopes, for there are no areas of subdued relief, apart from minor flood plains in the valley floors
(
Fig. 7.21)
.
It is not suggested that duricrusts are essential to the development of all slopes for as
explained in Chapter 6, dry upper zones of granite are relatively stable and have similar effects.
