1
The Solid Phase of Marine Sediments
16
developed a very detailed and purely descriptive
classification scheme (Fig. 1.10):
• The most frequently occurring component
with a percentage higher than 50 % determines the designation of the sediment. Nonbiogenic materials are specified accordingly
on the basis of the grain-size fractions: sand,
silt or clay. Biogenic material is referred to as
“ooze” and preceded by the most abundant
biogenic component: nannofossil ooze, foraminifera ooze, diatom ooze, and radiolarian
ooze respectively.
• Each component measuring between 25-50 %
is characterized by the following attributes:
sandy, silty, clayey, or nannofossil, foraminiferal, diatomaceous, or radiolarian.
• Components with percentages between 10-25 %
are referred to by adding the suffix “-bearing”,
as in “clay-bearing”, “diatom-bearing”.
• Components with percentages below 10 % are
not expressed at all, but may be included by
addition of the suffix “rich”, as in “C org -rich”.
The thus established, four-divided nomenclature of deep-sea sediments with threshold limits of
10 %, 25 % and 50 % easily permits a quite detailed categorization of the sediment which is
adaptable to generally rare, but locally frequent
occurrences of components, e.g. zeolite, eventually important for a more complete description.
1.4
Global Patterns of
Sediment Distribution
The overall distribution pattern of sediment types
in the world’s oceans depends on few elementary
factors. The most important factor is the relative
amount with which one particle species contributes to sediment formation. Particle preservation
and eventual dilution with other sediment components will modify the basic pattern. The formation
and dispersal of terrigenous constituents derived
from weathering processes on the continents, as
well as autochthonous oceanic-biogenic constituents, both strongly depend on the prevalent climate conditions, so that, in the oceans, a latitudedependent and climate-related global pattern of
sediment distribution will be the ultimate result.
1.4.1
Distribution Patterns of
Shelf Sediments
The particulate terrigenous weathering products
mainly transported from the continents by rivers
are not homogeneously distributed over the ocean
floor, but concentrate preferentially along the continental margins, captured either on the shelf or
the continental slope (Fig. 1.11). Massive sediment layers are built where continental inputs are
particularly high, and preferentially during glacial
periods when sea levels were low.
Approximately 70 % of the continental shelf
surface is covered with relict sediment, i.e. sediment deposited during the last glacial period under conditions different from today’s, especially at
times when the sea level was comparatively low
(Emery 1968). It has to be assumed that there is a
kind of textural equilibrium between these relict
sediments and recent conditions. The fine-grained
constituents of shelf sediments were eluted
during the rise of the sea level in the Holocene
and thereafter deposited, over the edge of the
shelf onto the upper part of the continental slope,
so that extended modern shelf surface areas
became covered with sandy relict sediment
(Milliman et al. 1972; Milliman and Summerhays
1975).
According to Emery (1968), the sediment distribution on recent shelves displays a plain and distinctly zonal pattern (Fig. 1.12):
Biogenic sediments with coarse-grained calcareous sediments predominate at lower latitudes,
Detrital sediments with riverine terrigenous
siliciclastic material at moderate latitudes, and
Glacial sediments of terrigenous origin transported by ice are limited to high latitudes.
In detail, this well pronounced pattern may become strongly modified by local superimpositions.
Coarse-grained biogenic carbonate sediments will
be found at moderate and high latitudes as well, at
places where the riverine terrigenous inputs are
very low (Nelson 1988).
Today, as a result of the post-glacial high sea
levels, most river-transported fine-grained material
is deposited in the estuaries and on the flat inner
shelves in the immediate proximity of river
mouths. Only a small proportion is transported
over the edge of the shelf onto the continental
slope. These processes account for the development of mud belts on the shelf, of which 5 types
The Solid Phase of Marine Sediments
16
developed a very detailed and purely descriptive
classification scheme (Fig. 1.10):
• The most frequently occurring component
with a percentage higher than 50 % determines the designation of the sediment. Nonbiogenic materials are specified accordingly
on the basis of the grain-size fractions: sand,
silt or clay. Biogenic material is referred to as
“ooze” and preceded by the most abundant
biogenic component: nannofossil ooze, foraminifera ooze, diatom ooze, and radiolarian
ooze respectively.
• Each component measuring between 25-50 %
is characterized by the following attributes:
sandy, silty, clayey, or nannofossil, foraminiferal, diatomaceous, or radiolarian.
• Components with percentages between 10-25 %
are referred to by adding the suffix “-bearing”,
as in “clay-bearing”, “diatom-bearing”.
• Components with percentages below 10 % are
not expressed at all, but may be included by
addition of the suffix “rich”, as in “C org -rich”.
The thus established, four-divided nomenclature of deep-sea sediments with threshold limits of
10 %, 25 % and 50 % easily permits a quite detailed categorization of the sediment which is
adaptable to generally rare, but locally frequent
occurrences of components, e.g. zeolite, eventually important for a more complete description.
1.4
Global Patterns of
Sediment Distribution
The overall distribution pattern of sediment types
in the world’s oceans depends on few elementary
factors. The most important factor is the relative
amount with which one particle species contributes to sediment formation. Particle preservation
and eventual dilution with other sediment components will modify the basic pattern. The formation
and dispersal of terrigenous constituents derived
from weathering processes on the continents, as
well as autochthonous oceanic-biogenic constituents, both strongly depend on the prevalent climate conditions, so that, in the oceans, a latitudedependent and climate-related global pattern of
sediment distribution will be the ultimate result.
1.4.1
Distribution Patterns of
Shelf Sediments
The particulate terrigenous weathering products
mainly transported from the continents by rivers
are not homogeneously distributed over the ocean
floor, but concentrate preferentially along the continental margins, captured either on the shelf or
the continental slope (Fig. 1.11). Massive sediment layers are built where continental inputs are
particularly high, and preferentially during glacial
periods when sea levels were low.
Approximately 70 % of the continental shelf
surface is covered with relict sediment, i.e. sediment deposited during the last glacial period under conditions different from today’s, especially at
times when the sea level was comparatively low
(Emery 1968). It has to be assumed that there is a
kind of textural equilibrium between these relict
sediments and recent conditions. The fine-grained
constituents of shelf sediments were eluted
during the rise of the sea level in the Holocene
and thereafter deposited, over the edge of the
shelf onto the upper part of the continental slope,
so that extended modern shelf surface areas
became covered with sandy relict sediment
(Milliman et al. 1972; Milliman and Summerhays
1975).
According to Emery (1968), the sediment distribution on recent shelves displays a plain and distinctly zonal pattern (Fig. 1.12):
Biogenic sediments with coarse-grained calcareous sediments predominate at lower latitudes,
Detrital sediments with riverine terrigenous
siliciclastic material at moderate latitudes, and
Glacial sediments of terrigenous origin transported by ice are limited to high latitudes.
In detail, this well pronounced pattern may become strongly modified by local superimpositions.
Coarse-grained biogenic carbonate sediments will
be found at moderate and high latitudes as well, at
places where the riverine terrigenous inputs are
very low (Nelson 1988).
Today, as a result of the post-glacial high sea
levels, most river-transported fine-grained material
is deposited in the estuaries and on the flat inner
shelves in the immediate proximity of river
mouths. Only a small proportion is transported
over the edge of the shelf onto the continental
slope. These processes account for the development of mud belts on the shelf, of which 5 types