396
Equation (8.16) inserted into (8.17) yields
U 2 = EU·
Ps
(8.18)
Pm -Ps
Using the same values as those above, the uplift in relation
to the normally subsiding basin floor is U 2 = 2.58 EU. This
signifies that a falling sea level in assoeiation with submarine erosion ean produee a very signifieant negative deviation from the "normal" subsidenee eurve (Fig. 8.6d' Curve
AD in eomparison with Curve AB).
(3) Eustatic sea-Ievel rise and starved sedimentation (Fig. 8.6e); the sediment thickness remains the
same as in (a). This scenario may still cause uplift,
U 3 , of the basin floor in relation to the normally subsiding basin. If the amplification factor for the growing sediment thickness from (a) to (b) is 1:, then h s =
1: h: or h: = 111: h s • By comparing columns (b) and (e)
on top of the isostatic compensation depth and again
using Eqs. (8.1) and (8.3), we find
U 3 = (I-.!..)h s Ps -pw -EU Pw
(8.19)
1:
Pm - Pw
Pm - Pw
In our example, with 't "" 1. 7 and other values as above,
we obtain U3 = 0.24 hs - 0.45 EU. Due to starved sedimentation, we get less subsidenee in this ease (Fig. 8.6e', Curve
AE) than in the normally sediment-filled basin without sealevel rise (Curve AB).
(4) Eustatie sea-Ievel rise and eontinued sedimentation (Fig. 8.6f). Sediment buildup is the same as
from (a) to (b). Comparing columns (b) and (f) and
applying Eqs. (8.1), and (8.3) or (8.5), we obtain the
additional subsidence, SI' superposed on the general
subsidence trend:
SI = EU P w
(8.20)
Pm -Pw
Fig. 8.6. Effects of changes in sediment buildup, h s ,
paleo-water depth, WD, and sea level, EU, on steady
subsidence as assumed for basin permanently filled
with sediment up to constant sea level (transition
from stage a to b). Deviations from the "normal"
curve of total subsidence (AB in b') are shown in e'g' and designated as relative uplift, U, and relative
subsidence, S. Each stage of e-g has to be compared
with b. Crustal parameters (thickness and density) as
weIl as average sediment density are assumed to remain constant. Isostatic compensation is Iocal (Airytype). SED is sediment buildup and ER is erosion.
e,e' Suhsequent to a, sedimentation ceases and basin
deepens to WD: reduced subsidence (Curve AC).
d,d' Eustatic sea-Ievel fall prevents sediment deposiChapter 8 Subsidence
For Pm = 3.33 glem 3 we obtain SI = 0.45 EU. In this exampie, however, the water depth is not only inereased by the
eustatie rise, EU, but by EU + SI = 1.45 EU.
Tbe additional subsidenee SI' eaused by sea level rise, is
the so-ealled hydro-isostatie effeet or hydro-isostasy. Tbe
resulting subsidenee (Curve AF) is steeper than the "normal" eurve AB (Fig. 8.7f).
(5) Eustatic sea level rise and inereased sediment
aeeumulation (Fig. 8.6g). Sediment buildup (h:"=
hs+Sz) reaches the pre-existing sea level. By comparing columns (h) and (g) we obtain
S2 = EU P w
Pm -Ps
(8.21)
By inserting the values used above, one obtains S 2 = 1.11
EU, i.e., subsidenee inereases signifieantly (eurve AG in
Fig. 8.6g').
In summary, the models ofFig. 18.6 and the data used for
the examples have yielded the following deviations from
the "normal" subsldenee eurve of a eompletely sedimentfilled basin at eonstant sea level. U values signify relative
uplift leading to a deereasing rate of subsidenee; S values
indieate relative subsidenee and thus an inereasing rate of
subsidenee:
(e) Ending sedimentation,
inereasing water depth, WD:
(d) Ending sedimentation,
sea level fall, and erosion:
(e) Ending sedimentation
and sea level rise:
(t) Sea level rise,
eontinuous sedimentation:
(g) Sea level rise,
inereasing sedimentation:
U I = 1.50WD
U2 =2.58 EU
U3 = 0.24 hs - 0.45 EU
SI = 0.45 EU
S2 = 1.11 EU
These examples demonstrate the order of magnitude
by which the subsidence curve of a particular basin
may deviate from a smooth, exponentially decaying
curve, which is usually expected for purely
endogenetic processes such as thermo-tectonic subsidence. Conversely, one can deduce the effects of
paleo-water depth, varying sedimentation rates intion and even leads to some erosion: greatly reduced
subsidence (CurIe AD). e,e' Eustatic sea-level rise,
but starved sedimentation: reduced subsidence
(Curve AE). f,i Eustatic sea level rise and sediment
accumulation as from a to b: increased subsidence
(Curve AF), but also increase in WD (Eu+S 1).
g,g' Sediment-fill up to "normal" sea level: strongly
increased subsidence (Curve AG). h Long-term subsidence curve composed of intervals with sedimentfilled basin (a,b) at normal sea level and intervals as
shown in e-g. "Normal" curve can be approximated
by interpolation. Deviations from this curve may be
used to calculate paleo-water depth and eustatic sea
level changes. All illustrations not to scale. For further explanation see text
Equation (8.16) inserted into (8.17) yields
U 2 = EU·
Ps
(8.18)
Pm -Ps
Using the same values as those above, the uplift in relation
to the normally subsiding basin floor is U 2 = 2.58 EU. This
signifies that a falling sea level in assoeiation with submarine erosion ean produee a very signifieant negative deviation from the "normal" subsidenee eurve (Fig. 8.6d' Curve
AD in eomparison with Curve AB).
(3) Eustatic sea-Ievel rise and starved sedimentation (Fig. 8.6e); the sediment thickness remains the
same as in (a). This scenario may still cause uplift,
U 3 , of the basin floor in relation to the normally subsiding basin. If the amplification factor for the growing sediment thickness from (a) to (b) is 1:, then h s =
1: h: or h: = 111: h s • By comparing columns (b) and (e)
on top of the isostatic compensation depth and again
using Eqs. (8.1) and (8.3), we find
U 3 = (I-.!..)h s Ps -pw -EU Pw
(8.19)
1:
Pm - Pw
Pm - Pw
In our example, with 't "" 1. 7 and other values as above,
we obtain U3 = 0.24 hs - 0.45 EU. Due to starved sedimentation, we get less subsidenee in this ease (Fig. 8.6e', Curve
AE) than in the normally sediment-filled basin without sealevel rise (Curve AB).
(4) Eustatie sea-Ievel rise and eontinued sedimentation (Fig. 8.6f). Sediment buildup is the same as
from (a) to (b). Comparing columns (b) and (f) and
applying Eqs. (8.1), and (8.3) or (8.5), we obtain the
additional subsidence, SI' superposed on the general
subsidence trend:
SI = EU P w
(8.20)
Pm -Pw
Fig. 8.6. Effects of changes in sediment buildup, h s ,
paleo-water depth, WD, and sea level, EU, on steady
subsidence as assumed for basin permanently filled
with sediment up to constant sea level (transition
from stage a to b). Deviations from the "normal"
curve of total subsidence (AB in b') are shown in e'g' and designated as relative uplift, U, and relative
subsidence, S. Each stage of e-g has to be compared
with b. Crustal parameters (thickness and density) as
weIl as average sediment density are assumed to remain constant. Isostatic compensation is Iocal (Airytype). SED is sediment buildup and ER is erosion.
e,e' Suhsequent to a, sedimentation ceases and basin
deepens to WD: reduced subsidence (Curve AC).
d,d' Eustatic sea-Ievel fall prevents sediment deposiChapter 8 Subsidence
For Pm = 3.33 glem 3 we obtain SI = 0.45 EU. In this exampie, however, the water depth is not only inereased by the
eustatie rise, EU, but by EU + SI = 1.45 EU.
Tbe additional subsidenee SI' eaused by sea level rise, is
the so-ealled hydro-isostatie effeet or hydro-isostasy. Tbe
resulting subsidenee (Curve AF) is steeper than the "normal" eurve AB (Fig. 8.7f).
(5) Eustatic sea level rise and inereased sediment
aeeumulation (Fig. 8.6g). Sediment buildup (h:"=
hs+Sz) reaches the pre-existing sea level. By comparing columns (h) and (g) we obtain
S2 = EU P w
Pm -Ps
(8.21)
By inserting the values used above, one obtains S 2 = 1.11
EU, i.e., subsidenee inereases signifieantly (eurve AG in
Fig. 8.6g').
In summary, the models ofFig. 18.6 and the data used for
the examples have yielded the following deviations from
the "normal" subsldenee eurve of a eompletely sedimentfilled basin at eonstant sea level. U values signify relative
uplift leading to a deereasing rate of subsidenee; S values
indieate relative subsidenee and thus an inereasing rate of
subsidenee:
(e) Ending sedimentation,
inereasing water depth, WD:
(d) Ending sedimentation,
sea level fall, and erosion:
(e) Ending sedimentation
and sea level rise:
(t) Sea level rise,
eontinuous sedimentation:
(g) Sea level rise,
inereasing sedimentation:
U I = 1.50WD
U2 =2.58 EU
U3 = 0.24 hs - 0.45 EU
SI = 0.45 EU
S2 = 1.11 EU
These examples demonstrate the order of magnitude
by which the subsidence curve of a particular basin
may deviate from a smooth, exponentially decaying
curve, which is usually expected for purely
endogenetic processes such as thermo-tectonic subsidence. Conversely, one can deduce the effects of
paleo-water depth, varying sedimentation rates intion and even leads to some erosion: greatly reduced
subsidence (CurIe AD). e,e' Eustatic sea-level rise,
but starved sedimentation: reduced subsidence
(Curve AE). f,i Eustatic sea level rise and sediment
accumulation as from a to b: increased subsidence
(Curve AF), but also increase in WD (Eu+S 1).
g,g' Sediment-fill up to "normal" sea level: strongly
increased subsidence (Curve AG). h Long-term subsidence curve composed of intervals with sedimentfilled basin (a,b) at normal sea level and intervals as
shown in e-g. "Normal" curve can be approximated
by interpolation. Deviations from this curve may be
used to calculate paleo-water depth and eustatic sea
level changes. All illustrations not to scale. For further explanation see text