Geology Reference
In-Depth Information
300
300
260
240
0
100
200
Time (kyr)
250
250
200
200
300
300
260
240
0
100
200
Time (kyr)
250
250
200
200
300
300
260
240
Fig. 9.
Modelling runs showing
superposition of short sea-level oscilla-
tions on long falling trend. Top panel:
no short oscillations; extended FST
forms on the slope. Middle panel:
sine waves of 5 m range, 23 kyr period
slightly modulate the surface of the
FST. Bottom panel: sine wave of 15 m
range, 23 kyr period subdivides the
FST into a series of downstepping plat-
forms. (Other settings: production rate
2000
0
100
200
Time (kyr)
250
250
200
200
m
m
0.0
km
0.1
0.2
0.3
0.4
0.5
0
100
200
300
400
500
Distance in modelling space (m)
m yr
1
, no erosion.)
intervals of the case studies. The minimum rates
were derived by assuming that rate scaling does
apply and the minima in White (1984) had to
be further reduced using the scaling formula of
Gardner
et al
. (1987).
Marine erosion is very poorly constrained on
a formation scale. Rates sustained for 50 kyr and
longer were assumed to vary between 75 and
750
Rates of sea-level fall were gleaned directly
from sequence geometry and age dates of each
case study (arranged in stratigraphic order).
(1)
Habshan
(after Droste & Van Steenwinkel,
2004; H. Droste, pesonal communication):
the Early Cretaceous Habshan Formation of
Oman consists of six cycles with forced-
regression (= FST) deposits. The range of fall
is 60-70 m, duration of cycles about 1-3 Myr.
Assuming that the FST represents 50% of
the cycle duration yields rates of fall of
40-140
m yr
1
subaerial equivalents using the regression formula
of Fig. 6. It seems unlikely that marine erosion
rates of 200
m yr
1
, which translates into 10-100
m yr
1
(subaerial equivalent) derived
from the maximum rates of notch erosion in the
Holocene can be sustained for time intervals repre-
sented by the case studies in question. No rate scal-
ing was applied to the minimum because the effect
on the total erosion rate was considered negligible.
m yr
1
.
Shu'aiba of Bu Hasa
(2)
(after Fitchen, 1997): the
FST of the Upper Shu'aiba Formation occupies
the time between the sequence boundary 109.5
and 108.7 Ma, i.e. 0.8 Myr. The range of fall is
