Geologist Indonesia

1. Ocean Sediments

2. Definition ocean Sediments
• Ocean sediments are unconsolidated organic and
inorganic particles that accumulate on the ocean floor.
• Ocean sediments originate from numerous sources
– weathering and erosion of the continents
(terrigenous/lithogenous)
– volcanic eruptions (volcanogenous) included in
terrigenous sediments.
– biological activity (biogenous)
– chemical processes within the oceanic crust and
seawater (Hydrogenous/autigenous)
– impacts of extra-terrestrial objects (cosmogenous)

3. Sediments
Chemical
Volcano Physical Cosmogen
Existing rocks weathering
Weathering
Transport by water, ice and winds
solution solid
precipitation deposition
Terrigenous piroclasts Cosmogen
Chemical Biogenous
Evaporites Limestone Conglomerate Tuffs Cosmogen
Tefra ous dust
Anhydrite Chert Sand
pyroclasts Tektites
Mn nodules Silt
spherules
Clay

4. 4-2
Sedimentation in the Ocean
Deep-sea Sedimentation has two main sources of
sediment: external- terrigenous material from the land
and internal-biogenic and authigenic from the sea.
Sedimentation in the Deep Sea

5. Grain size and current velocity affect the
deposition and erosion of sediment.
– Smallest and largest particles
behave similarly with respect to
transportation and erosion.
– Sand in the middle of the graph
takes the least amount of energy to
erode.
– Larger particles require more
energy to erode because they’re
heavy. It takes a stronger current to
lift them off the bottom.
– Particles smaller than sand also
take more energy to erode. Smaller Hjulstrom’s diagram
particles (especially clay) tend to
be cohesive.
12 - 5

6. Classification
• 1. Clasification by origin
– a. Terrigenous - erosional products (also volcanics)
composed of fragments of pre-existing rock material
– b. Biogenous - composed of hard remains of once-
living organisms. shells
– c. Hydrogenous - formed when dissolved materials
come out of solution (precipitate) (in situ
precipitation). Desolved materials form as a result
weathering
– d. Cosmogenous - extraterrestrial (derived from outer
space)

7. Percentage of Sediment type in
the Ocean
% of all ocean
Sediment type floor covered
Terrigenous ～ 45%
Biogenous ～ 55%
Hydrogenous <1%
(authigenic)
Cosmogenous very small amount

8. Classified by size according to the
Wentworth scale
• 2. Clasification based on size
– a. Gravel (pebbles, cobbles) = > 2mm
– b. Sand = 62 µm - 2 mm
– c. Silt = 4 - 62 µm
– d. Clay = < 4 µm
• Grain sizes are classified by using formula:
Φ = -log2d
Φ phi is Wentworth scale
d = diametre of the grains

9. Sediment Size Wentworth scale

10. • 1. By Constituents
– a. Pelagic sediments - open ocean, fine grained
• clays & biogenic oozes
– b. Hemipelagic - continental margin, coarser grained
• muds

11. Major Sediment Input to the Oceans
Source Amount (109 tons/yr)
Rivers 18.3
Glaciers and ice sheets 2.0
Wind blown dust 0.6
Coastal erosion 0.25
Volcanic debris 0.15
Groundwater <0.48

12. Terrigenous (or Lithogenous
Sediments):
• Derived from weathering of rocks at or
above sea level (e.g., continents, islands)
• Two distinct chemical compositions
ferromagnesian, or iron-magnesium
bearing minerals
non-ferromagnesian minerals – e.g.,
quartz, feldspar, micas
• Largest deposits on continental margins
(less than 40% reach abyssal plains)
• Transported by water, wind, gravity,
and ice
• Transported as dissolved and
suspended loads in rivers, waves,
longshore currents

13. Sedimentation Processes on the
Continental Shelf
• Tides, waves, and currents strongly affect
continental-shelf sedimentation.
– Shoreline turbulence: waves are one of the most
notable influences because it keeps particles from
settling. Surf and waves carry small particles out to
sea. Their affect diminishes further from shore.

14. • Sediments are also
transported to the open-
ocean by gravity-driven
turbidity currents.
• Dense 'slurries' of
suspended sediment
moved as turbulent
underflows
• Typically initiated by storm
activity or earthquakes
• Initial flow often confined
to submarine canyons of
the continental shelf and
slope
• Form deep-sea fans
where the mouth of the
canyon opens onto the
continental rise

15. River input of silt to ocean

16. • Sediment delivered to
the open-ocean by
Wind
wind activity as
Blown
particulate matter Sand
(dust) West
• Primary dust source is Africa
deserts in Asia and
North Africa
• Comprise much of the
fine-grained deposits in
remote open-ocean
areas (red clays)
• Volcanic eruptions
contribute ash to the
atmosphere which Pinatubo
settles within the June
oceans 1991

17. • Boulder to clay size particles
also eroded and transported
to oceans via glacial ice
• Glacier termination in circum-
polar oceans results in calving
and iceberg formation
• As ice (or icebergs) melt,
entrained material is
deposited on the ocean floor
• Termed 'ice-rafted' debris or
diamictites.

18. Pelagic lithogenous sediments
• Sources of fine material:
– Volcanic ash (volcanic
eruptions)
– Wind-blown dust
– Fine grained material
transported by deep
ocean currents
- Abyssal clay (red clay)
– Oxidized iron

19. Composition of Red Clay
• Clay minerals: montmorillonite, illite, chlorite,
kalonite, and mixed-layer derivatives
• Lithogenous minerals: feldspar, pyroxene,
quartz
• Hydrogenous (or authigenic) minerals: zeolite
and ferromanganese oxides and hydroxides.

20. Distribution of Clay Minerals
The clay mineral which are most abundant in deep sea clay
are montmorillonite and illite
Fig.8.8 Clay mineral distribution on the ocean floor. The map shows the dominant mineral
in the fraction less than 2 ㎛ . Mixture indicates that no one clay mineral exceeds 50% of

21. Hemipelagic Sediments
• Characteristic of the
continental slope & rise
• Muds carried across
shelf by wave & tide
energy as slightly dense
plumes
– extend out from slope
at depth where denser
water is encountered
• Relatively fast
sedimentation rate
• Hemipelagic mud is
generally gray or green
from the presence of
sulfides or magnetite

23. Biogenous Sediments:
• composed primarily of marine microfossil remains
• shells of one-celled plants and animals, skeletal fragments
• median grain size typically less than 0.005 mm (i.e., silt or
clay size particles)
• characterized as CaCO3 (calcium carbonate) or SiO2 (silica)
dominated systems
• sediment with biogenic component less than 30% termed
calcareous, siliceous clay
• calcareous or siliceous 'oozes' if biogenic component greater
than 30%

24. planktonic
foraminifera
• Oozes consist of biogenous
minterals: shells of planktonic
foraminifera, radiolarians,
coccolithophores, and diatoms.
• About one half of the deep sea radiolarians
floor is covered by oozes.
• The most important factors
controlling the composition of
biogenous deep sea sediments
are fertility and depth.
coccolithophores
• Fertility controls the supply of
plankton remains, while depth
controls the dissolution of
carbonate (through pressure
and water mass chemistry). diatoms

25. Controlling Factors
Fig.8.4 Distribution of major facies in a depth-fertility frame, based on sediment
patterns in the eastern central Pacific. Numbers are typical sedimentation rates in
mm/1000 yr(which is the same as m/million yr). [Source as for Fig.8.2]

26. Distribution of calcareous material

27. Calcareous oozes
• Consist of foraminifera, coccolithophores and pteropods
which cover ~50% of the ocean floor
– distribution controlled largely by dissolution processes
– cold, deep waters are undersaturated with respect to
CaCO3
– deep water is slightly acidic as a result of elevated
CO2 concentrations
– solubility of CaCO3 also increases in colder water and
at greater pressures
– CaCO3 therefore readily dissolved at depth
• level below which no CaCO3 is preserved is the
carbonate compensation depth
• typically occurs at a depth of 3000 to 4000 m

28. • Calcium carbonate dissolves better in colder water, in acidic
water, and at higher pressures. In the deep ocean, all three
of these conditions exist. Therefore, the dissolution rate of
calcium carbonate increases greatly below the thermocline.
This change in dissolution rate is called the lysocline.
Below the lysocline, more and more calcium carbonate
dissolves, until eventually, there is none left. The depth
below which all calcium carbonate is dissolved is called the
carbonate compensation depth or CCD.

29. calcareous ooze

30. Patterson (1542) showed a
drastic increase of dissolution
rates below 3500 m in the
central Pacific.

31. Dissolution patterns in the deep sea
• The CCD is the particular
depth level at any one
place in the ocean where
the rate of supply of
calcium carbonate to the
sea floor is balanced by
the rate of dissolution, so
that there is no net
accumulation of carbonate. Generalized diagrams illustrating the
relative position of calcite and aragonite
• ACD (Aragonite solubility profiles in the modern tropical
Compensation Depth) ocean and the variation in temperature
with depth. The major zones of
• CCD (Calcite digenesis are plotted to the right.
Compensation Depth)

32. Figure 5-17
Calcium Carbonate in the ocean

33. Lysocline
• Another CCD-like level
which can be mapped to
describe dissolution
patterns is the lysocline.
• The concept of the
lysocline was introduced
to denote a contour-
following boundary zone
between well-preserved
and poorly-preserved
foraminiferal
assemblages on the floor
of the central Atlantic
Ocean and on that of the
South Pacific.
• The lysocline marks the
top of the Antarctic
Bottom Water.

34. White Cliffs of Dover
Formation of
calcareous
deposits
• composed largely of foraminifera and
coccolithophores
http://en.wikipedia.org/wiki/White_cliffs_of_Dover

35. Carbonate Shelves
• Carbonate sediments and reefs form in warm shallow
water regions where the influx of terrigenous materials is
low.

36. Plate stratigraphy
• Developed at the mid-oceanic ridge
• The axial rift valley is flank with hosts which covered by biogenic sediments
• As the spreading continues the hosts subsides below the CCD the biogenic
sediments are overlain by pelagic red clay.
•The stratigraphy of the plate consists of Basalt at the bottom, and is overain by
biogenic sediments and finally red clay.

37. Siliceous Ooze
• Distribution, production, and
dissolution patterns of the siliceous
deposits
• Remains of diatoms, silicoflagellates
and radiolarians, and sponge
spicules, all of which are made of
opal, a hydrated form of amorphous
silicon oxide.
• Diatom oozes are typical for high
latitudes, diatom muds for
pericontinental regions, and
radiolarian oozes for equatorial areas.

38. The siliceous deposits typically occur in areas of
high fertility; that is, in regions of surface water
with relatively high phosphate values.
Fig.8.15 Flux of siliceous fossil to the sea floor.[W. H. Berger, J. C.
Herguera, in P. G. Falkowski. A. D. Woodhead. eds, 1992, Primary
productivity and biogeochemical cycles in the sea. Plenum Press, New

39. Siliceous ooze
• Seawater undersaturated with silica
• Siliceous ooze commonly associated with high biologic
productivity in surface ocean

40. Distribution of neritic and pelagic marine
sediments

41. Silica content in the ocean

42. Controlling factors
• The formation of siliceous rocks is controlled by
• the rate of production of siliceous organisms in
the overlying waters
• the degree of dilution by terrigenous, volcanic,
and calcareous particles
• the extent of dissolution of the siliceous skeletons

43. • There is a distinct negative correlation between silica
and calcite distributional patters.
• increasing fertility leads to decreasing preservation of
calcite, but increasing accumulation of silica.
• A similarly opposing trend is indicated for depth
relationships, with silica corrosion being greatest in
upper waters, that of carbonate being greatest at depth

44. Deep sea cherts
• Silicified sediments cemented by cryptocrystalline and
microcrystalline quartz
• appears to proceed from mobilization and reprecipitation
of opal, generating a disordered cristobalite (=fibrous
quartz) which eventually alters toward a quartzitic rock
with mostly quartz-replaced and quartz-filled fossils as
diagenesis progresses.

45. © The Open University

46. Hydrogenous (or Authigenic) Sediments
• produced by chemical processes in seawater
• essentially solid chemical precipitates of several
common forms
• Non-biogenous carbonates
– form in surface waters supersaturated with calcium
carbonate
– common forms include short aragonite crystals and
oolites

47. • Phosphorites
– phosphate crusts (containing greater than 30% P2O5)
occurring as nodules
– formed as large quantities of organic phosphorous
settle to the ocean floor
– unoxidized material is transformed to phosphorite
deposits
– found on continental shelf and upper slope in regions
of high productivity

48. • Manganese nodules
– surficial deposits of
manganese, iron,
copper, cobalt, and
nickel
– accumulate only in
areas of low
sedimentation rate
(e.g., the Pacific)
– develop extremely
slowly (1 to 10
mm/million years)

49. • evaporites ('salt'
deposits')
– occur in regions of
enhanced evaporation
(e.g., Isolated seas, Red
Sea. Persian Gulf and
Dead Sea)
– evaporative process Dead Sea
Jordan,
removes water and
leaves a salty brine
– Consist of gypsum,
anhidrite, halite.

50. • The term evaporites is used for all deposits, such as salt
deposits, mainly chemical sediments that are composed
of minerals that precipitated from saline solutions
concentrated by evaporation. Evaporite deposits are
composed dominantly of varying proportions of halite
(rock salt) (NaCl), anhydrite (CaSO4) and gypsum
(CaSO4.2H2O). Evaporites may be classified as
chlorides, sulfates or carbonates on the basis of their
chemical composition (Tucker, 1991).

52. Cosmogenous Sediments:
• sediments derived from
extraterrestrial materials
• includes micrometeorites and
tektites
• tektites result from collisions
with extraterrestrial materials
– fragments of earth's crust
melt and spray outward from
impact crater
– crustal material re-melts as it
falls back through the
atmosphere
– forms 'glassy' tektites