8.3 Rift Basin Models and Observed Subsidence
407
a
HI8ERNIA 0-35
(m)
15
10
5
150
100
AGE (Ma)
50
o
PALEO-WATER DEPlH
50
li
o
4
5
o
~2
E
C
jE 3
'8ASEMENT'
COMPACTED
o ~
18 !ß
ce
37 C3
40 Z
::::l
o
!Xl
77
100
120
135
145
U
I
a..
~
Cl
~
CI)
LL
160 0 w
Cl
<{
HI8ERNIA
GABRIEL
Q.
W
o
4
~--------- lHEOREnCAL
Fig. 8.14. Example of subsidenee
and burial history from Grand
Banks eontinental margin, northwestern Atlantie. a Sedimentation rates at weH Hibernia 0-35.
b Variations in water depths,
eompaetion and burial histories
of stratigraphie units (total sub sidenee) at weH Hibernia 0 -35. c
Inferr~d thermo-teetonie subsidenee of three Grand Banks weHs
as eompared to theoretieal eurves
for thinned eontinental ernst with
60% dike injeetions and pure
oeeanic ernst. (After Agterberg
and Gradstein 1988)
5
6~-----r-----r-----r-----r-----r-----,
lHEOREnCAL
150
120
90
60
30
Examples of Simulated and Observed Subsidence
Gulf of California, young passive margin. The
rifting phase of the very young passive eontinental
margin at the southem tip of Baja Califomia (cf.
Seets. 4.3 and 12.8, Figs. 4.5 and 11.19) was eharaeterized by a "normal" subsidenee rate (around 200
m/Ma, Curray et a1. 1982b). With the onset of oeean
spreading (drifting phase) in the southem Gulf of
Califomia 3 to 4 Ma ago, subsidenee aeeelerated up
to at least 1000 mlMa for a very short interval, before
slowing down again (Fig. 8.l2a),
o (Ma)
Northwestern Atlantic. Subsidenee and burial history at single sites, based on deep driHholes with wen
studied stratigraphie seetions, have been studied,
among many other examples, in the Grand Banks
area, offNewfoundland (Fig. 8.14).
Weil Hibernia 0-35 was drilled on the edge of a graben
whieh has been subsiding sinee the early Jurassie; Puffin
B-90 is near the southern trans form margin of the Grand
Banks; and Gabriel C-60 lies farther east elose to the edge
of subsided eontinental ernst. The latter two wells were
affeeted by rifting later than Hibernia (Fig. 8.14e). All
three sites are eharaeterized by a lower Cretaeeous elastie
wedge (sedimentation rate 10-25 emlka) with a major sand