Geology Reference
In-Depth Information
Superposition of sea-level cycles
3000
Most runs were made with the simplest possible
sea-level movement for FST development -
linear fall at constant rate. Clearly, this is a drastic
simplifi cation, albeit a useful one. It is well estab-
lished that sea-level movements occur in a wide
range of timescales (review in Harrison, 2002).
Stratigraphic sequences, too, have been shown
to occur in a wide range of temporal and spatial
scales such that large sequences usually can be
broken down into smaller building blocks. A num-
ber of runs addressed the effect of superposition
of sea-level cycles on FST development. These
runs assumed long linear rises and falls of sea
level, modulated by higher-frequency sine waves.
Figure 9 shows that these oscillations produce a
segmentation of the FST including episodes with
prograding, fl at-topped platforms. Subaerial ero-
sion may break up the FST into isolated steps that
mark the downward shift of the production zone.
600
2000
1500
400
1000
750
Regression line
y = 0.1387 x
200
500
300
( r 2 = 0.9615)
200
150
0
0
2000
Marine erosion (
4000
m yr 1 )
μ
Fig. 6. Comparison of effi ciency of marine and subaerial
erosion in destroying FST. Each dot represents cross plot
of the marine and subaerial erosion rate required to create
the standard model at a given carbonate production rate.
Red numbers: production rate in
Real-world examples as 'ground truth'
for modelling
m yr 1 .
Well-documented examples from the geological
record are an essential check of the modelling results.
This section fi rst presents two examples of falling-
stage systems tracts where C3D modelling was part
of the analysis, followed by case studies where C3D
modelling was not applied but the relevant rates
are suffi ciently well constrained to plot them in the
parameter space established by modelling.
third dimension is indicated by showing the
FST-STM boundaries of different production
levels in different colours. The bi-logarithmic
plot of Fig. 8b demonstrates that the modelling
data points of the sea-level-erosion plane form
long straight segments, i.e. they indeed resem-
ble power functions in a wide range of condi-
tions. However, the slopes of the regression lines
may differ considerably from 1, thus the match
with hyperbolas of the type x
Miocene Nijar Basin, Spain
The Nijar Basin belongs to a series of intramon-
tane basins on the rump of the Betic Cordillera,
an alpine fold-and-thrust belt in southeast-
ern Spain. The basin fi ll is well exposed, easily
accessible and has been repeatedly studied in
recent decades (Dabrio et al ., 1981; Franseen &
Mankiewicz, 1991; Mankiewicz, 1996). Warrlich
et al . (2005, 2008) proposed a formal sequence
stratigraphy. Depositional sequence E of this suc-
cession is dated as 6.2-5.9 Ma (Messinian) and
includes a well-developed FST (Figs 10 and 11).
This FST has been modelled in C3D (Warrlich,
2001) and the results are shown here for compari-
son (Fig. 12).
y = constant is
not perfect. Figure 8c illustrates the FST-STM
boundary in a view perpendicular to the sea-
level-erosion plane. In this plot, each coloured
hyperbola of Fig. 8a is represented by one dot,
taking advantage of the fact that the product of
rate-of-fall times rate-of-erosion is constant for
all points of a particular hyperbola. The value
of the dot was calculated by multiplying rate
of fall and rate of erosion for the data points
near the apex of the hyperbolas, where the lines
fi t the data rather well. The graph shows that
with increasing production, the FST-STM
boundary shifts away from the origin. The points
approximately follow the curve y = 0.000037
Early Cretaceous Shu'aiba Formation,
Middle East
x 1.28 , where y is the production rate and x is the
product of rate of fall and rate of erosion. This
curve resembles a parabola but with an exponent
of 1.28 rather than 2.
The Shu'aiba Formation of the Trucial Coast
(e.g. Bu Hasa Field) and Oman (e.g. Safah Field) is
 
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