222 Deep-Sea Sediments - Patterns, Processes, and Stratigraphic Methods
The fact that fecal transport makes up a high proportion of the pelagic rain implies
that biological patterns in surface waters dominate not only the sources of sediments
in the deep sea, but also the patterns of transport. There is one interesting corollary
(among many): the more mineral matter is available for inclusion in fecal pellets (e.
g., eolian dust), the more efficiently nutrients are removed from surface waters, by
particles. This mechanisms of "fast stripping", by enhanced settling, presumably is
responsible for the fact that little nutrient-rich (or muddy) water reaches the open sea,
from the coastal zone.
In the following we shall take a closer look at the major types of deep-sea deposits
resulting from the pelagic rain: "red clay" (in fact, reddish brown), calcareous ooze,
siliceous ooze. Manganese nodules will be discussed in the section on resources
(Chap. 10).
8.4 "Red Clay" and "Clay Minerals"
8.4.1 Origin of "Red Clay": the Questions. Of all deposits, "red clay" is uniquely
restricted to the deep-sea environment. The bulk of the components are extremely
fine-grained, and the coarse silt and sand fractions consist of particles originating in
the ocean: hydrogenous minerals, volcanogenic debris, ferromanganese concretions,
and traces of biogenous particles such as fish teeth, arenaceous forams, and in some
cases, spicules and radiolarians.
What is the source of "red clay"? This question is really two questions in one.
The first question addresses the ultimate source: to what extent is the clayey
fraction in pelagic clays derived from in situ decomposition of volcanic material, and
what is the contribution from continents and other sources?
The second question concerns transportation: what is the relative importance of
transport by wind versus transport by rivers and ocean currents in bringing continentderived clay particles to their site of deposition?
8.4.2 Composition of "Red Clay". To answer the questions posed (how much of the
clay is of oceanic, how much of continental origin; and how did it get there?), we
need to know the composition of the fine-grained constituents, their distribution on the
sea floor and their accumulation rates. Analyses by X-ray diffraction began in the
1930s (R. Revelle in the Pacific, C. W. Correns in the Atlantic) and have been greatly
improved and systematically applied to deep-sea deposits since. The following minerals are important in the clay and fine silt fractions of "red clay" (see Appendix A4):
1. Clay minerals: smectite, illite, chlorite, kaolinite, and mixed-layer derivatives;
2. Lithogenous minerals; feldspar, pyroxene, quartz;
3. Hydrogenous (or authigenic) minerals: zeolite and ferromanganese oxides and
hydroxides.
The latter provide much of the X-ray amorphous material present in "red clay".
Iron-oxide minerals with Fe 3 +, typical for oxygen-rich environments, are responsible
for the red to brown colors.
The fact that fecal transport makes up a high proportion of the pelagic rain implies
that biological patterns in surface waters dominate not only the sources of sediments
in the deep sea, but also the patterns of transport. There is one interesting corollary
(among many): the more mineral matter is available for inclusion in fecal pellets (e.
g., eolian dust), the more efficiently nutrients are removed from surface waters, by
particles. This mechanisms of "fast stripping", by enhanced settling, presumably is
responsible for the fact that little nutrient-rich (or muddy) water reaches the open sea,
from the coastal zone.
In the following we shall take a closer look at the major types of deep-sea deposits
resulting from the pelagic rain: "red clay" (in fact, reddish brown), calcareous ooze,
siliceous ooze. Manganese nodules will be discussed in the section on resources
(Chap. 10).
8.4 "Red Clay" and "Clay Minerals"
8.4.1 Origin of "Red Clay": the Questions. Of all deposits, "red clay" is uniquely
restricted to the deep-sea environment. The bulk of the components are extremely
fine-grained, and the coarse silt and sand fractions consist of particles originating in
the ocean: hydrogenous minerals, volcanogenic debris, ferromanganese concretions,
and traces of biogenous particles such as fish teeth, arenaceous forams, and in some
cases, spicules and radiolarians.
What is the source of "red clay"? This question is really two questions in one.
The first question addresses the ultimate source: to what extent is the clayey
fraction in pelagic clays derived from in situ decomposition of volcanic material, and
what is the contribution from continents and other sources?
The second question concerns transportation: what is the relative importance of
transport by wind versus transport by rivers and ocean currents in bringing continentderived clay particles to their site of deposition?
8.4.2 Composition of "Red Clay". To answer the questions posed (how much of the
clay is of oceanic, how much of continental origin; and how did it get there?), we
need to know the composition of the fine-grained constituents, their distribution on the
sea floor and their accumulation rates. Analyses by X-ray diffraction began in the
1930s (R. Revelle in the Pacific, C. W. Correns in the Atlantic) and have been greatly
improved and systematically applied to deep-sea deposits since. The following minerals are important in the clay and fine silt fractions of "red clay" (see Appendix A4):
1. Clay minerals: smectite, illite, chlorite, kaolinite, and mixed-layer derivatives;
2. Lithogenous minerals; feldspar, pyroxene, quartz;
3. Hydrogenous (or authigenic) minerals: zeolite and ferromanganese oxides and
hydroxides.
The latter provide much of the X-ray amorphous material present in "red clay".
Iron-oxide minerals with Fe 3 +, typical for oxygen-rich environments, are responsible
for the red to brown colors.