Geology Reference
In-Depth Information
Table 1.
Calculated foreland basin parameters using equations from Allen and Allen (2005).
Flexural rigidity,
D
(dyne cm)
Air-fi lled
r
f
= 0.0
Water-fi lled
r
f
= 1.0
Sediment-fi lled
r
f
= 2.5
(a) Basin width - distance from load to edge of peripheral bulge (in km)
10
28
44
48
61
10
29
78
85
109
10
30
139
151
193
10
31
247
269
344
10
32
439
478
611
10
33
780
851
1087
(b) Distance from load to top of peripheral bulge (in km)
10
28
58
64
82
10
29
104
113
145
10
30
185
202
258
10
31
329
359
458
10
32
585
638
815
10
33
1040
1135
1450
(c) Width of peripheral bulge (in km)
10
28
58
64
82
10
29
104
113
145
10
30
185
202
258
10
31
329
359
458
10
32
585
638
815
10
33
1040
1135
1450
(d) Width of secondary basin (back-bulge basin; in km)
10
28
58
64
82
10
29
104
113
145
10
30
185
202
258
10
31
329
359
458
10
32
585
638
815
10
33
1040
1135
1450
Depending on fl exural rigidity and whether the
basin is fi lled with air, water or sediment, the
width of the basin may range from 44 to 1087 km
(Table 1). Given the values of fl exural rigidity
most commonly reported (Allen & Allen, 2005),
basin widths of 100-300 km are typical for most
sediment-fi lled foreland basins.
For elastic plates, peripheral bulges should be
approximately one-third wider (
Width
bulge
) than
their associated foreland basin:
In other words, uplift on the bulge should be
approximately 4% of the subsidence in the basin.
For a 1000-m deep fl exure, this translates into
only 40 m of uplift. Because the width of the peri-
pheral bulge is likely to be greater than a hundred
kilometres, slopes on the fl anks of the peripheral
bulge will be negligible (less than 0.1°). Distal to
the peripheral bulge is an area of minor subsidence
generated by fl exure, sometimes called the back-
bulge basin (Decelles & Giles, 1996). The amount
of subsidence in this basin is related to the amount
of subsidence at the load by the relationship:
(4)
Given typical values of fl exural rigidity, periph-
eral bulges associated with sediment-fi lled basins
should be 130-390 km wide (Table 1). The height
of a peripheral bulge should scale linearly with
the maximum amount of subsidence in the basin
(that is, subsidence at the load), regardless of the
type of fi ll in the basin:
(6)
which is less than 0.2% of the subsidence at the
load. For a 1000-m deep fl exure, this translates
into a mere 2 m of subsidence. So, although sedi-
mentary basins commonly are developed on the
distal side of the peripheral bulge, it is unlikely
that their origin is solely or even primarily driven
by fl exure related to thrust loading.
(5)
