Chapter 4
Marine Sediments
Essentials of Oceanography
7th Edition
Ocean sediment
Various materials settle through the water
column and accumulate on the ocean floor
Layers represent a record of Earth history,
including:
Movement of tectonic plates
Past changes in climate
Ancient ocean circulation patterns
Cataclysmic events
Collecting ocean sediment
Specially
designed ships
collect cores by
rotary drilling
Cores allow
scientists to
analyze ocean
sediment
Figure 4B
The 4 main types of sediment
1. Lithogenous = composed of fragments of
pre-existing rock material
2. Biogenous = composed of hard remains of
once-living organisms
3. Hydrogenous = formed when dissolved
materials come out of solution (precipitate)
4. Cosmogenous = derived from outer space
Origin of lithogenous sediment
Forms by:
Weathering =
breakup of exposed
rock
Transportation =
movement of
sediment
Deposition =
settling and
accumulation
Sediment-transporting media
Figure 4-4
Lithogenous sediment
composition
Most lithogenous
sediment is
composed of
quartz, which is:
Abundant
Chemically stable
Durable
Figure 4-5
Lithogenous sediment texture
Texture
includes:
Grain size
Sorting
Rounding
Maturity
Figure 4-7
Distribution of lithogenous
sediment
Lithogenous sediment occurs as:
Neritic (nearshore) deposits
Beaches
Continental shelves
Turbidites
Glacial-rafted debris
Pelagic (deep ocean floor) deposits
Abyssal clay
Origin of biogenous sediment
Organisms that produce hard parts die
Material rains down on the ocean floor and
accumulates as:
Macroscopic shells, bones, teeth
Microscopic tests (shells)
If comprised of at least 30% test material, called
biogenous ooze
Biogenous sediment composition
Microscopic biogenous tests are
composed of 2 main chemical compounds:
1.
Silica (SiO2) including opal (SiO2 · nH2O)
Diatoms (algae)
Radiolarians (protozoan)
2.
Calcium carbonate or calcite (CaCO3)
Coccolithophores (algae)
Foraminifers (protozoan)
Examples of silica-secreting
microscopic organisms
Diatom
Radiolarian
Figure 4-8
Siliceous ooze
Silica-secreting
organisms
accumulate to form
siliceous ooze
(>30% siliceous
test material)
Figure 4-8c
Examples of calcite-secreting
microscopic organisms
Coccolithophores
Foraminifers
Figure 4-9
Calcareous ooze
Calcite-secreting
organisms
accumulate to form
calcareous ooze
(>30% calcareous
test material)
Figure 4-9d
Biogenous ooze turns to rock
When biogenous
ooze hardens and
lithifies, can form:
Diatomaceous earth
(if composed of
diatom-rich ooze)
Chalk (if composed
of coccolith-rich
ooze)
Chalk cliffs of southern England
Figure 4-10
Distribution of biogenous ooze
Most biogenous ooze found as pelagic
deposits
Factors affecting the distribution of
biogenous ooze:
Productivity (amount of organisms in surface
waters)
Destruction (dissolving at depth)
Dilution (mixing with lithogenous clays)
Distribution of siliceous ooze
Silica slowly but
steadily dissolves
in seawater
Siliceous ooze
found where it
accumulates faster
than it dissolves
Figure 4-11
Distribution of calcareous ooze
Calcite dissolves
beneath the calcite
compensation depth
(CCD) at 4.5 km
Calcareous ooze can
be found below the
CCD if it is buried
and transported to
deep water
Figure 4-12
Biogenous ooze as
environmental indicator
Surface water
temperature
Main locations
found
Siliceous ooze
Cool
Calcareous ooze
Warm
Sea floor
beneath cool
surface water in
high latitudes;
upwelling areas
Sea floor
beneath warm
surface water in
low latitudes; not
too deep (CCD)
Origin of hydrogenous sediment
Hydrogenous sediment forms when
dissolved materials come out of solution
(precipitate)
Precipitation is caused by a change in
conditions including:
Changes in temperature
Changes in pressure
Addition of chemically active fluids
Types of hydrogenous sediment
Manganese nodules
Phosphates
Carbonates
Metal sulfides
Evaporite salts
Mining
manganese
nodules
Figure 4-25
Evaporite
salts
Figure 4-15
Cosmogenous sediment
Cosmogenous sediment is
composed of material derived
from outer space
Two main types:
Microscopic space dust
2. Macroscopic meteor debris
1.
Forms an insignificant
proportion of ocean sediment
Microscopic
cosmogenous
spherule
Figure 4-16
Mixtures
Most ocean sediment is a mixture of
sediment types
One type of sediment usually dominates,
allowing it to be classified as primarily:
Lithogenous
Biogenous
Hydrogenous
Cosmogenous
Worldwide distribution of neritic
and pelagic sediment
Figure 4-17
Ocean sediments as a resource
Ocean sediments contain
many important resources,
including:
Petroleum
Gas hydrates
Sand and gravel
Evaporative salts
Phosphorite
Manganese nodules and
crusts
Offshore drilling rig
Figure 4-21
End of Chapter 4
Essentials of Oceanography
7th Edition