502
b
- CO
~
-- E
CI)
E
a:
Cf)
c:
CO
Q)
~
Chapter 11 Sediment Supply, Subsidence, and Basin Fill
Extensional basin
a
Closing basin
200
Observation point
Ad
Ab~
Ad/~:~';~'~'~ ~,:\~ .. ~~.~~.~.~.~.:~.-' T ~~~~.
e.9. 3000/1000 km 2
. ':"~'
or elongate basins
and land areas
600/200 km wide
Ritt basin (Rate of extension 0.25 cm/a; Wj = 50 km,
or 2.5 cm/a; Wj = 500 km)
p"'1.92
-
3 E
~
2
CIl
CIl
Q)
c:
~
()
.s::.
----\"-----------p=2.5 g/cm3 )
- - - - - - - - - - - - - - - - - - - - - - - - -
30
40
50
60 Ma
~
0.5
Water depth
O~~~TJ'7~~~T/~_r/'7i~~~~I:~
2
.s::. +-'
a.
Q)
o 3
_ Initial tectonic ____________ ~
subsidence
(50 m/Ma)
,
I
~--- Surplus of sediment (bypassing) - - - - - - - -- ---.>I
4
not completely
sediment-filled
4
--,
Fig. 11.13. Sediment filling of rift basin; basin evolutIOn begins with basin widths of W=50 km or 500
km and Ai Ab =2; rates of extension 0.25 or 2.5 cm/a,
respectively. a Cross sections of elongate extensional
and closing model basins (basin area Ab) and their
drainage areas (A d ). b Mean mechanical sedimentation rates, SR",c' of fully compacted (p=2.5 g/cm 3 )
and porous Sealment (lower mean bulk density, increasing with accumulated sediment thickness). The
mechanical denudation rate is D~e=50 mmlka
(global mean). c Tectonic and thermal subsidence
enhanced by sediment load
shown for a relatively low mechanical denudation
rate of 25 mmlka controlling the SR 25 curve in the
diagram.
Short-term variations in the mechanical denudation
rate and the related sedimentation rate (decreasing
with time) are envisaged in Fig. 11.14b which resembles Fig. 11.13b.
To completely fill the widening basin with sediment, the
sediment thickness in the basin should grow as indicated
by a broken line (same curve as that for complete basin
filling in Fig. 13b). This can be accomplished for a long
time period when sediment influx is high (DR me =50 curve).
With lower sediment influx the continental phase of the
basin fill becomes shorter as mentioned above.