1
1
The Solid Phase of Marine Sediments
DIETER K. FÜTTERER
1.1
Introduction
The oceans of the world represent a natural depository for the dissolved and particulate products of continental weathering. After its input, the
dissolved material consolidates by means of biological and geochemical processes and is deposited on the ocean floor along with the particulate
matter from weathered rock. The ocean floor deposits therefore embody the history of the continents, the oceans and their pertaining water
masses. They therefore provide the key for understanding Earth’s history, especially valuable for
the reconstruction of past environmental conditions of continents and oceans. In particular, the
qualitative and quantitative composition of the
sedimentary components reflect the conditions of
their own formation. This situation may be more or
less clear depending on preservation of primary
sediment composition, but the processes of early
diagenesis do alter the original sediment composition, and hence they alter or even wipe out the
primary environmental signal. Hence, only an
entire understanding of nature and sequence of
processes in the course of sediment formation and
its diagenetic alteration will enable us to infer the
initial environmental signal from the altered
composition of the sediments.
Looking at the sea-floor sediments from a
geochemical point of view, the function of particles, or rather the sediment body as a whole, i.e.
the solid phase, can be quite differently
conceived and will vary with the perspective of
the investigator. The “classical” approach –
simply applying studies conducted on the
continents to the oceans – usually commences
with a geological-sedimentological investigation,
whereafter the mineral composition is recorded in
detail. Both methods lead to a more or less overall
geochemical description of the entire system.
Another, more modern approach conceives the
ocean sediments as part of a global system in
which the sediments themselves represent a
variable component between original rock source
and deposition. In such a rather process-related
and globalized concept of the ocean as a system,
sediments attain special importance. First, they
constitute the environment, a solid framework for
the geochemical reactions during early diagenesis
that occur in the pore space between the particles
in the water-sediment boundary layer. Next to the
aqueous phase, however, they are simultaneously
starting material and reaction product, and
procure, together with the porous interspaces, a
more or less passive environment in which
reactions take place during sediment formation.
1.2
Sources and Components of
Marine Sediments
Ocean sediments are heterogeneous with regard
to their composition and also display a considerable degree of geographical variation. Due to the
origin and formation of the components various
sediment types can be distinguished: Lithogenous sediments which are transported and dispersed into the ocean as detrital particles, either
as terrigenous particles – which is most frequently the case – or as volcanogenic particles
having only local importance; biogenous sediments which are directly produced by organisms
or are formed by accumulation of skeletal fragments; hydrogenous or authigenic sediments
which precipitate directly out of solution as new
formations, or are formed de novo when the particles come into contact with the solution; finally,
cosmogenic sediments which are only of secondary importance and will therefore not be considered in the following.
1
The Solid Phase of Marine Sediments
DIETER K. FÜTTERER
1.1
Introduction
The oceans of the world represent a natural depository for the dissolved and particulate products of continental weathering. After its input, the
dissolved material consolidates by means of biological and geochemical processes and is deposited on the ocean floor along with the particulate
matter from weathered rock. The ocean floor deposits therefore embody the history of the continents, the oceans and their pertaining water
masses. They therefore provide the key for understanding Earth’s history, especially valuable for
the reconstruction of past environmental conditions of continents and oceans. In particular, the
qualitative and quantitative composition of the
sedimentary components reflect the conditions of
their own formation. This situation may be more or
less clear depending on preservation of primary
sediment composition, but the processes of early
diagenesis do alter the original sediment composition, and hence they alter or even wipe out the
primary environmental signal. Hence, only an
entire understanding of nature and sequence of
processes in the course of sediment formation and
its diagenetic alteration will enable us to infer the
initial environmental signal from the altered
composition of the sediments.
Looking at the sea-floor sediments from a
geochemical point of view, the function of particles, or rather the sediment body as a whole, i.e.
the solid phase, can be quite differently
conceived and will vary with the perspective of
the investigator. The “classical” approach –
simply applying studies conducted on the
continents to the oceans – usually commences
with a geological-sedimentological investigation,
whereafter the mineral composition is recorded in
detail. Both methods lead to a more or less overall
geochemical description of the entire system.
Another, more modern approach conceives the
ocean sediments as part of a global system in
which the sediments themselves represent a
variable component between original rock source
and deposition. In such a rather process-related
and globalized concept of the ocean as a system,
sediments attain special importance. First, they
constitute the environment, a solid framework for
the geochemical reactions during early diagenesis
that occur in the pore space between the particles
in the water-sediment boundary layer. Next to the
aqueous phase, however, they are simultaneously
starting material and reaction product, and
procure, together with the porous interspaces, a
more or less passive environment in which
reactions take place during sediment formation.
1.2
Sources and Components of
Marine Sediments
Ocean sediments are heterogeneous with regard
to their composition and also display a considerable degree of geographical variation. Due to the
origin and formation of the components various
sediment types can be distinguished: Lithogenous sediments which are transported and dispersed into the ocean as detrital particles, either
as terrigenous particles – which is most frequently the case – or as volcanogenic particles
having only local importance; biogenous sediments which are directly produced by organisms
or are formed by accumulation of skeletal fragments; hydrogenous or authigenic sediments
which precipitate directly out of solution as new
formations, or are formed de novo when the particles come into contact with the solution; finally,
cosmogenic sediments which are only of secondary importance and will therefore not be considered in the following.