Geology Reference
In-Depth Information
Climate
Sediment
production
Sediment
availability
Transport
capacity
Cumulative
Dry system
response
Sand-starved
conditions
Sand-sea
destruction
Arid
Lagged
transport-
limited influx
Sand-sea
construction
(dune
growth and
accumulation)
Lagged
availability-
limited influx
Stored
sediment
Sand-sea
stabilization
Humid
Time
0
+
0
+
0
+
Figure 14.8
Process-response model for Saharan sand seas based on sediment production, sediment availability (supply),
and transport capacity. The system is driven by a climatic cycle from humid to arid, shown on the left. An explanation is
given in the text.
Source:
Adapted from Kocurek (1998)
Box 14.2
DUNE PATTERNS IN SAND SEAS: THE HISTORICAL DIMENSION
The dune forms in a sand sea are primarily a response to
wind conditions and sand supply. Nonetheless, the pat-
tern of dunes in many sand seas is much more intricate
and requires more complex explanations (Lancaster
1999). Recent research points to the significance of sea-
level and climatic changes in affecting sediment supply,
sediment availability, and wind energy. The upshot of
such changes is the production of different generations
of dunes. So the varied size, spacing, and nature of
dunes in sand seas catalogue changes in sand supply,
sand availability, and sand mobility that have produced
many superimposed generations of dune forms, each
of a distinct type, size, alignment, and composition.
In addition, the large dunes that characterize sand
seas - compound dunes and complex dunes, mega-
dunes, and draa - commonly seem to be admixtures
of several phases of dune building, stabilization, and
reworking. The indications are that, rather than being
solely the production of contemporary processes, the
form of sand seas is partly inherited, and to unlock
the historical processes involved requires investigations
of past conditions affecting sand accumulation. Vast
sand accumulations take much time to grow. Ergs with
very large dunes, as in the Arabian Peninsula, North
Africa, and central Asia, may have taken a million or
more years to form (Wilson 1971). Certainly, cycles of
