Sea-Level
Sediment Dynamics
Tidal Depositional Systems
Tsunamis
Waves
MARGINAL SEAS
Di Zhou
South China Sea Institute of Oceanology, Chinese
Academy of Sciences, Guangzhou, China
Synonyms
Marginal basin; Back-arc basin; Back-arc sea
Definition
In geology, a marginal sea is the sea bordering continents,
semi-isolated from open ocean by island arc or land ridge,
and underlain by oceanic crust (Karig, 1971). Thus a marginal sea is a deep-sea basin with water depth in general
over ~3,000 m, while its slopes and shelves are called as
its continental margins.
As a geographic and oceanographic term, a “marginal
sea” represents a partially enclosed sea adjacent to or
widely open to open ocean at the surface, but bounded
by submarine ridges on the seafloor (Wikipedia). The
presence of oceanic crust is not required.
As a geopolitical term, a marginal sea is equivalent
to a territorial water, which is important in determining
what maritime resources that a state can exploit
(Wikipedia).
Geographic distribution
The marginal seas in geological context are distributed
mainly in western Pacific Ocean, forming a giant sea chain
of ~12,000 km long from the north to the south. A small
number of marginal seas are seen in Caribbean, Andaman,
and off Antarctica. See Figure 1 for the names and locations of the marginal seas. The Gulf of California is
regarded as having oceanic crust in its southern portion
and thus may be considered as a marginal sea in geological
context (Curry et al., 1982).
The marginal seas in geography and oceanography context include not only the marginal seas in geological context but also their continental margins, as well as other
semi-enclosed seas such as the Arabian Sea, Baltic Sea,
Bay of Bengal, Bering Sea, Beaufort Sea, Black Sea, Gulf
of Mexico, the Mediterranean Sea, Red Sea, Ross Sea,
Weddell Sea, all four of the Siberian seas (Barents, Kara,
Laptev, and East Siberian) [Water Encyclopedia], Yellow
Sea, East China Sea, and Bohai Sea.
Features and formation models of marginal seas in
geological context
History of the concept
Although the term “marginal sea” appeared much earlier
in context of geography and oceanography, the clear definition of marginal sea or marginal basin in the geological
context was given several years after establishment of
plate tectonics (Karig, 1971). Early researches on marginal seas concentrated to their nature and origin
(Matsuda and Uyeda, 1971; Packham and Falvey, 1971;
Sleep and Toksöz, 1971). Then there were a long period
of extensive geological and geophysical investigations
including ocean drilling, which revealed basic features
and led to various formation models of marginal seas
(cf. the summary in Tamaki and Honza (1991)). Recent
studies of marginal seas have extended to climate and
environmental impacts of the marginal seas in the present
and in the geological history (Wang, 1999).
Features
Marginal seas in geological context are of similar water
depths as normal oceans, but different from open oceans
in several aspects (Tamaki and Honza, 1991; Wang,
1999): (1) Almost all marginal seas are located on the east
side of a continent and separated from an open ocean by a
trench-arc system. (2) Marginal seas have a short life span
from their opening by the breakup of lithosphere to the
stop of seafloor spreading, usually less than 25 Ma. After
the cessation of spreading, many marginal seas are closed
by subduction of themselves. (3) Marginal seas may
change their spreading directions due to the movements
of surrounding tectonic terrains. (4) Compared with open
oceans of the same age, marginal seas usually have
600–800 m deeper water depths. (5) The marginal seas
in geographic context are the sites for active land-sea
interactions and have one to two orders of magnitude
higher deep-water sedimentation rates, larger mass flux
and energy flux, and higher biodiversity compared with
open oceans.
Formation models
The formation of a marginal sea is indicated by the generation of oceanic crust as the consequence of lithosphere
breakup and seafloor spreading. The models of formation
mechanism of marginal seas can be grouped into three categories: back-arc spreading models, the slab-pull model,
and the pull-apart model. Because most marginal seas
are formed behind island arcs, several formation models
focus on the mechanism of back-arc spreading
(Figure 2), which may be grouped further into active
models (Models 1 and 2) in which asthenosphere flow
provides the driving force for the opening of marginal
sea, and passive models where the driving force is slab
movement, either the retreat of the overriding back-arc
continental slab (Model 3) or the retreat of the subducting
oceanic slab (Models 4 and 5).
MARGINAL SEAS
423
Sediment Dynamics
Tidal Depositional Systems
Tsunamis
Waves
MARGINAL SEAS
Di Zhou
South China Sea Institute of Oceanology, Chinese
Academy of Sciences, Guangzhou, China
Synonyms
Marginal basin; Back-arc basin; Back-arc sea
Definition
In geology, a marginal sea is the sea bordering continents,
semi-isolated from open ocean by island arc or land ridge,
and underlain by oceanic crust (Karig, 1971). Thus a marginal sea is a deep-sea basin with water depth in general
over ~3,000 m, while its slopes and shelves are called as
its continental margins.
As a geographic and oceanographic term, a “marginal
sea” represents a partially enclosed sea adjacent to or
widely open to open ocean at the surface, but bounded
by submarine ridges on the seafloor (Wikipedia). The
presence of oceanic crust is not required.
As a geopolitical term, a marginal sea is equivalent
to a territorial water, which is important in determining
what maritime resources that a state can exploit
(Wikipedia).
Geographic distribution
The marginal seas in geological context are distributed
mainly in western Pacific Ocean, forming a giant sea chain
of ~12,000 km long from the north to the south. A small
number of marginal seas are seen in Caribbean, Andaman,
and off Antarctica. See Figure 1 for the names and locations of the marginal seas. The Gulf of California is
regarded as having oceanic crust in its southern portion
and thus may be considered as a marginal sea in geological
context (Curry et al., 1982).
The marginal seas in geography and oceanography context include not only the marginal seas in geological context but also their continental margins, as well as other
semi-enclosed seas such as the Arabian Sea, Baltic Sea,
Bay of Bengal, Bering Sea, Beaufort Sea, Black Sea, Gulf
of Mexico, the Mediterranean Sea, Red Sea, Ross Sea,
Weddell Sea, all four of the Siberian seas (Barents, Kara,
Laptev, and East Siberian) [Water Encyclopedia], Yellow
Sea, East China Sea, and Bohai Sea.
Features and formation models of marginal seas in
geological context
History of the concept
Although the term “marginal sea” appeared much earlier
in context of geography and oceanography, the clear definition of marginal sea or marginal basin in the geological
context was given several years after establishment of
plate tectonics (Karig, 1971). Early researches on marginal seas concentrated to their nature and origin
(Matsuda and Uyeda, 1971; Packham and Falvey, 1971;
Sleep and Toksöz, 1971). Then there were a long period
of extensive geological and geophysical investigations
including ocean drilling, which revealed basic features
and led to various formation models of marginal seas
(cf. the summary in Tamaki and Honza (1991)). Recent
studies of marginal seas have extended to climate and
environmental impacts of the marginal seas in the present
and in the geological history (Wang, 1999).
Features
Marginal seas in geological context are of similar water
depths as normal oceans, but different from open oceans
in several aspects (Tamaki and Honza, 1991; Wang,
1999): (1) Almost all marginal seas are located on the east
side of a continent and separated from an open ocean by a
trench-arc system. (2) Marginal seas have a short life span
from their opening by the breakup of lithosphere to the
stop of seafloor spreading, usually less than 25 Ma. After
the cessation of spreading, many marginal seas are closed
by subduction of themselves. (3) Marginal seas may
change their spreading directions due to the movements
of surrounding tectonic terrains. (4) Compared with open
oceans of the same age, marginal seas usually have
600–800 m deeper water depths. (5) The marginal seas
in geographic context are the sites for active land-sea
interactions and have one to two orders of magnitude
higher deep-water sedimentation rates, larger mass flux
and energy flux, and higher biodiversity compared with
open oceans.
Formation models
The formation of a marginal sea is indicated by the generation of oceanic crust as the consequence of lithosphere
breakup and seafloor spreading. The models of formation
mechanism of marginal seas can be grouped into three categories: back-arc spreading models, the slab-pull model,
and the pull-apart model. Because most marginal seas
are formed behind island arcs, several formation models
focus on the mechanism of back-arc spreading
(Figure 2), which may be grouped further into active
models (Models 1 and 2) in which asthenosphere flow
provides the driving force for the opening of marginal
sea, and passive models where the driving force is slab
movement, either the retreat of the overriding back-arc
continental slab (Model 3) or the retreat of the subducting
oceanic slab (Models 4 and 5).
MARGINAL SEAS
423