PALEOPHYSIOGRAPHY OF OCEAN BASINS
R. Dietmar Müller and Maria Seton
School of Geosciences, The University of Sydney,
Sydney, NSW, Australia
Synonyms
Paleogeography of Ocean Basins
Definition
Plate motions and the history of plate boundary geometries through time are the primary drivers for the largescale paleophysiography of the ocean basins. These in turn
determine the history of seafloor spreading and subduction, driving the time dependence of the age-area distribution of ocean floor. The depth of the ocean floor and
volume of the ocean basins are primarily dependent on
its age. Reconstructions of the age and depth distribution
of the ocean floor combined with estimates of sediment
thickness through time and the reconstruction of oceanic
plateaus yield broad-scale paleophysiographic maps of
the ocean basins.
Introduction
The paleophysiography of the ocean basins relies on an
understanding of the current physiography of the oceans
and the processes governing its development through geological time. The most fundamental parameter driving the
depth distribution of ocean basins is the age of the oceanic
lithosphere. The recognition that age and depth are linked
via the cooling of oceanic lithosphere as newly formed
crust moves away from mid-ocean ridges provides a
framework for mapping ocean basin depth through time.
Constructing a present-day physiographic map of the
oceans is relatively straightforward due to the preservation
of oceanic lithosphere. However, to generate complete
oceanic physiographic maps in the past involves recreating ocean crust that has since been subducted. This
becomes progressively more difficult back through time.
History
Turcotte and Oxburgh (1967) were the first to suggest that
the subsidence of the seafloor away from mid-ocean
ridges can be explained by the cooling of the lithosphere
as a thermal boundary layer. Ten years later, a major analysis of the relationship between depth and age of the ocean
floor (Parsons and Sclater, 1977) showed that the cooling
of a simple rigid boundary layer can explain the depth–
age relationship of crust younger than 80 Ma of age. For
older ocean floor, the depth was shown to increase asymptotically to a constant value, i.e., to “flatten.” The flattening of the depth implied the addition of extra heat under
the older ocean floor. Parsons and Sclater (1977) showed
that a plate of constant thickness gave a good approximation to this concept and gave birth to so-called plate
models describing oceanic depth–age relationships. The
severe computational restrictions during the 1970s compared to today’s standards meant that the observational
parameter space could not be efficiently explored for the
best-fit solution. A formal best-fit solution was first found
by Stein and Stein (1992) via their widely used GDH1
model (global depth and heat flow #1). More recently,
Crosby and McKenzie (2009) suggested a revised
age-depth curve by adding a damped sinusoidal perturbation to the flattening of seafloor older than 80 Ma. This
approach is based on the observed sinusoidal shallowing
of the reference depth–age curve for the North Pacific
and to a lesser extent the North Atlantic between the ages
of 80 and 130 Ma. They argued that this sinusoidal
shallowing resembles the results of early numerical
models where a surface boundary layer cools by conduction and then becomes unstable once its local Rayleigh
number exceeds a critical value. The growing instability
then suddenly increases as the base of the lithospheric
boundary layer falls off and is replaced by hotter asthenosphere from below. The new material then cools again by
conduction, until it in turn becomes unstable, resulting in a
series of decaying oscillations about an asymptotic steadystate value. As well as these “thermal” models, there exist
other age-depth models, which are categorized as either
“dynamic” or “chemical” models. In dynamic models,
increasing pressure in the asthenosphere prevents the seafloor from subsiding (Phipps Morgan and Smith, 1992).
Chemical models take into account the compositional
and rheological stratification on small-scale convection
(Afonso et al., 2008) or consider the lateral flow and
spreading of depleted, buoyant mantle residuum left over
from the melt extraction process at mid-ocean ridges
(Phipps Morgan et al., 1995). Despite the ongoing debate
about the details of the depth–age relationship of relatively old ocean floor, models such as GDH1 are a good
approximation to construct paleophysiographic ocean
basin models. Other uncertainties such as the effect of
large-scale mantle convection on oceanic depth
(Spasojevic and Gurnis, 2012) and uncertainties in the elevation of oceanic plateaus and sediment thickness through
time (Müller et al., 2008b) potentially play a large role in
reconstructing the paleo-depth of ocean basins.
Reconstructing mid-ocean ridges and flanks
The reconstruction of the ocean basins relies on a global
plate motion model to establish the location and geometry
of mid-ocean ridges through time. This is achieved
through marine magnetic anomaly identifications, geological information such as paleomagnetic data from terranes
and microcontinents (especially in the Tethys Ocean),
mid-ocean ridge subduction events, and the rules of plate
tectonics (Cox and Hart, 1986). Uncertainties in
reconstructing mid-ocean ridges and flanks grow progressively as you travel back through time as more and more
mid-ocean ridge flanks are subducted and, hence, need
to be recreated. Even though the details of now subducted
mid-ocean ridge geometries cannot be known, reasonable
638
PALEOPHYSIOGRAPHY OF OCEAN BASINS
R. Dietmar Müller and Maria Seton
School of Geosciences, The University of Sydney,
Sydney, NSW, Australia
Synonyms
Paleogeography of Ocean Basins
Definition
Plate motions and the history of plate boundary geometries through time are the primary drivers for the largescale paleophysiography of the ocean basins. These in turn
determine the history of seafloor spreading and subduction, driving the time dependence of the age-area distribution of ocean floor. The depth of the ocean floor and
volume of the ocean basins are primarily dependent on
its age. Reconstructions of the age and depth distribution
of the ocean floor combined with estimates of sediment
thickness through time and the reconstruction of oceanic
plateaus yield broad-scale paleophysiographic maps of
the ocean basins.
Introduction
The paleophysiography of the ocean basins relies on an
understanding of the current physiography of the oceans
and the processes governing its development through geological time. The most fundamental parameter driving the
depth distribution of ocean basins is the age of the oceanic
lithosphere. The recognition that age and depth are linked
via the cooling of oceanic lithosphere as newly formed
crust moves away from mid-ocean ridges provides a
framework for mapping ocean basin depth through time.
Constructing a present-day physiographic map of the
oceans is relatively straightforward due to the preservation
of oceanic lithosphere. However, to generate complete
oceanic physiographic maps in the past involves recreating ocean crust that has since been subducted. This
becomes progressively more difficult back through time.
History
Turcotte and Oxburgh (1967) were the first to suggest that
the subsidence of the seafloor away from mid-ocean
ridges can be explained by the cooling of the lithosphere
as a thermal boundary layer. Ten years later, a major analysis of the relationship between depth and age of the ocean
floor (Parsons and Sclater, 1977) showed that the cooling
of a simple rigid boundary layer can explain the depth–
age relationship of crust younger than 80 Ma of age. For
older ocean floor, the depth was shown to increase asymptotically to a constant value, i.e., to “flatten.” The flattening of the depth implied the addition of extra heat under
the older ocean floor. Parsons and Sclater (1977) showed
that a plate of constant thickness gave a good approximation to this concept and gave birth to so-called plate
models describing oceanic depth–age relationships. The
severe computational restrictions during the 1970s compared to today’s standards meant that the observational
parameter space could not be efficiently explored for the
best-fit solution. A formal best-fit solution was first found
by Stein and Stein (1992) via their widely used GDH1
model (global depth and heat flow #1). More recently,
Crosby and McKenzie (2009) suggested a revised
age-depth curve by adding a damped sinusoidal perturbation to the flattening of seafloor older than 80 Ma. This
approach is based on the observed sinusoidal shallowing
of the reference depth–age curve for the North Pacific
and to a lesser extent the North Atlantic between the ages
of 80 and 130 Ma. They argued that this sinusoidal
shallowing resembles the results of early numerical
models where a surface boundary layer cools by conduction and then becomes unstable once its local Rayleigh
number exceeds a critical value. The growing instability
then suddenly increases as the base of the lithospheric
boundary layer falls off and is replaced by hotter asthenosphere from below. The new material then cools again by
conduction, until it in turn becomes unstable, resulting in a
series of decaying oscillations about an asymptotic steadystate value. As well as these “thermal” models, there exist
other age-depth models, which are categorized as either
“dynamic” or “chemical” models. In dynamic models,
increasing pressure in the asthenosphere prevents the seafloor from subsiding (Phipps Morgan and Smith, 1992).
Chemical models take into account the compositional
and rheological stratification on small-scale convection
(Afonso et al., 2008) or consider the lateral flow and
spreading of depleted, buoyant mantle residuum left over
from the melt extraction process at mid-ocean ridges
(Phipps Morgan et al., 1995). Despite the ongoing debate
about the details of the depth–age relationship of relatively old ocean floor, models such as GDH1 are a good
approximation to construct paleophysiographic ocean
basin models. Other uncertainties such as the effect of
large-scale mantle convection on oceanic depth
(Spasojevic and Gurnis, 2012) and uncertainties in the elevation of oceanic plateaus and sediment thickness through
time (Müller et al., 2008b) potentially play a large role in
reconstructing the paleo-depth of ocean basins.
Reconstructing mid-ocean ridges and flanks
The reconstruction of the ocean basins relies on a global
plate motion model to establish the location and geometry
of mid-ocean ridges through time. This is achieved
through marine magnetic anomaly identifications, geological information such as paleomagnetic data from terranes
and microcontinents (especially in the Tethys Ocean),
mid-ocean ridge subduction events, and the rules of plate
tectonics (Cox and Hart, 1986). Uncertainties in
reconstructing mid-ocean ridges and flanks grow progressively as you travel back through time as more and more
mid-ocean ridge flanks are subducted and, hence, need
to be recreated. Even though the details of now subducted
mid-ocean ridge geometries cannot be known, reasonable
638
PALEOPHYSIOGRAPHY OF OCEAN BASINS