8 Subsidence
8.1 General Meehanisms Controlling Subsidenee
8.1.1 Isostasy
Initial Subsidenee (Without Thermal Effeets)
Water-Filled Basins
Sediment-Filled Basins
Thermal Uplift and Subsidenee
8.1.2 Flexural Response of the Crust to Loading
8.1.3 Mineral Phase Transitions
8.1.4 Summary (Meehanisms Causing Subsidenee)
8.2 Methods for Determining Subsidenee of
Sedimentary Basins
8.2.1 Introduetion
8.2.2 Sediment Deeompaetion
8.2. 3 Teetonie Subsidenee from Deeompaetion and
Isostatie Adjustment
8.2.4 Effeets ofPaleo-Bathymetry and
Sea-Level Changes
8.2.5 Summary (Subsidenee History Analysis)
8.3 Subsidenee ofModel Basins and Observed
Subsidenee History
8.3.1 Rift Basin Models and Observed Subsidenee
The MeKenzie Extension Model
Finite Rifting Time and Lateral Heat Transfer
Sediment Fill and Crustal Flexure
Modified Rift Models and Diseussion
Subsidenee from Geohistory Analysis
Young Rift Systems
Older Continental Rift Zones
8.3.2 Passive Margin Models and
Observed Subsidenee
General Coneepts
Examples of Simulated and
Observed Subsidenee
8.3.3 Summary (Simulated and Observed Subsidenee)
8.4 Subsidenee Related to Teetonie Loading, Subduetion,
and Strike-Slip Motion
8.4.1 Foreland Basins
General Aspeets and Problems
Subsidenee Curves from Geohistory Analysis
8.4.2 Subduetion-Related Are-Treneh Systems
8.4.3 Pull-Apart Basins
8.4.4 Summary (Subsidenee Caused by
Teetonie Loads, ete.)
8.1 General Mechanisms
Controlling Subsidence
8.1.1 Isostasy
Substantial sediment aeeumulation and the fonnation
of sedimentary basins result from ernstal subsidenee.
At least in the beginning of basin fonnation, teetonie
subsidenee must predate sedimentation, whereas
later, subsidenee rnay also be aetively driven by an
inereasing sediment load (total subsidenee). In this
ehapter, the different meehanisms leading to erustal
subsidenee as well as some models quantifying the
development of subsidenee versus time, i.e., subsidenee his tory eurves, are briefly introdueed.
In most eases, teetonie subsidenee of the land surfaee or sea floor is eontrolled by the prineiple of
isostasy, thennal eontraetion of the lithosphere,
and/or flexuralloading (Fig. 8.1). Aeeording to the
present view of isostasy, the elevation of the top of
the ernst is a funetion of the thieknesses and densities
of several layers. These are from top to bottom: sea
water, sediments, solid erust eonsisting of igneous
and metamorphie roeks, and solid upper mantle or
rnantle lithosphere (Fig. 8.1) resting on the viseous
asthenosphere (rnantle asthenosphere). Within the
asthenosphere, horizontal surfaees of eonstant pressure ean be assumed, whieh implies that the mass per
unit area of the overlying roek eolurnn is everywhere
the same. Henee one ean write:
pA + p,h, + Pehe + Pmh.n
+ Paha = eonstant
(8.1)
wh~re the layers (with thiekness h) are sea water, w,
sediment, s, ernst, e, mantle lithosphere, m, and rnantle asthenosphere, a. Density values, p, of these layers are listed in Fig. 8.1. The mass of the atmosphere
per unit area is negleeted in Eq. (8.1).
The base of the lithosphere is assumed to be a temperature boundary (approximately 1350°C). The hotter mantle asthenosphere has a somewhat lower density than the overlying mantle lithosphere. Thiekening of the ernst at the expense of the mantle lithosphere eauses uplift of the land surfaee or sea bottom, whereas thiekening of the rnantle lithosphere at
the expense of the ernst is followed by subsidenee.
8.1 General Meehanisms Controlling Subsidenee
8.1.1 Isostasy
Initial Subsidenee (Without Thermal Effeets)
Water-Filled Basins
Sediment-Filled Basins
Thermal Uplift and Subsidenee
8.1.2 Flexural Response of the Crust to Loading
8.1.3 Mineral Phase Transitions
8.1.4 Summary (Meehanisms Causing Subsidenee)
8.2 Methods for Determining Subsidenee of
Sedimentary Basins
8.2.1 Introduetion
8.2.2 Sediment Deeompaetion
8.2. 3 Teetonie Subsidenee from Deeompaetion and
Isostatie Adjustment
8.2.4 Effeets ofPaleo-Bathymetry and
Sea-Level Changes
8.2.5 Summary (Subsidenee History Analysis)
8.3 Subsidenee ofModel Basins and Observed
Subsidenee History
8.3.1 Rift Basin Models and Observed Subsidenee
The MeKenzie Extension Model
Finite Rifting Time and Lateral Heat Transfer
Sediment Fill and Crustal Flexure
Modified Rift Models and Diseussion
Subsidenee from Geohistory Analysis
Young Rift Systems
Older Continental Rift Zones
8.3.2 Passive Margin Models and
Observed Subsidenee
General Coneepts
Examples of Simulated and
Observed Subsidenee
8.3.3 Summary (Simulated and Observed Subsidenee)
8.4 Subsidenee Related to Teetonie Loading, Subduetion,
and Strike-Slip Motion
8.4.1 Foreland Basins
General Aspeets and Problems
Subsidenee Curves from Geohistory Analysis
8.4.2 Subduetion-Related Are-Treneh Systems
8.4.3 Pull-Apart Basins
8.4.4 Summary (Subsidenee Caused by
Teetonie Loads, ete.)
8.1 General Mechanisms
Controlling Subsidence
8.1.1 Isostasy
Substantial sediment aeeumulation and the fonnation
of sedimentary basins result from ernstal subsidenee.
At least in the beginning of basin fonnation, teetonie
subsidenee must predate sedimentation, whereas
later, subsidenee rnay also be aetively driven by an
inereasing sediment load (total subsidenee). In this
ehapter, the different meehanisms leading to erustal
subsidenee as well as some models quantifying the
development of subsidenee versus time, i.e., subsidenee his tory eurves, are briefly introdueed.
In most eases, teetonie subsidenee of the land surfaee or sea floor is eontrolled by the prineiple of
isostasy, thennal eontraetion of the lithosphere,
and/or flexuralloading (Fig. 8.1). Aeeording to the
present view of isostasy, the elevation of the top of
the ernst is a funetion of the thieknesses and densities
of several layers. These are from top to bottom: sea
water, sediments, solid erust eonsisting of igneous
and metamorphie roeks, and solid upper mantle or
rnantle lithosphere (Fig. 8.1) resting on the viseous
asthenosphere (rnantle asthenosphere). Within the
asthenosphere, horizontal surfaees of eonstant pressure ean be assumed, whieh implies that the mass per
unit area of the overlying roek eolurnn is everywhere
the same. Henee one ean write:
pA + p,h, + Pehe + Pmh.n
+ Paha = eonstant
(8.1)
wh~re the layers (with thiekness h) are sea water, w,
sediment, s, ernst, e, mantle lithosphere, m, and rnantle asthenosphere, a. Density values, p, of these layers are listed in Fig. 8.1. The mass of the atmosphere
per unit area is negleeted in Eq. (8.1).
The base of the lithosphere is assumed to be a temperature boundary (approximately 1350°C). The hotter mantle asthenosphere has a somewhat lower density than the overlying mantle lithosphere. Thiekening of the ernst at the expense of the mantle lithosphere eauses uplift of the land surfaee or sea bottom, whereas thiekening of the rnantle lithosphere at
the expense of the ernst is followed by subsidenee.