LECTURE NOTES:
OCEANOGRAPHY (MARSC 100),
SNYDER, L.
CH. 5: Marine Sediments
Marine Sediments: Loose organic or inorganic particulate material that accumulates,
unconsolidated, on the seafloor.
Why study Sediments?
1. Ocean’s & Earth’s “recent” history
Crust constantly recycled ~ 180 million years
2. Catastrophic events (asteroid 65 mya)
3. Past, present & future
Global Climate
Ocean/Atmosphere Conditions
4. Ocean resources
Oil & natural gas
Sand & lime (cement)
What Creates Sediments?
Weathering: Breakdown of rocks by chemical or mechanical processes
Erosion: Transport of loose weathered material from land to sea
Biologic remains
Volcanism
Chemical processes (water)
Space debris
Classifying Sediments
1. Particle Size: large grains deposited closest to shore, small grains (dust) carried by
currents & wind to ocean basins
 Settling Time
2. Sorting: Organized by grain size
 Well-sorted – sediment composed of same size particles
 Poorly sorted – sediment made up of particles of various sizes
3. Source: Origin (4 categories)
a. Terrigenous Sediments: Inorganic minerals (Granite, quartz, clay)
 Most abundant
 Volcanic eruption, land erosion, blown dust (EX: Dust from Gobi Desert: Asia to
Pacific)
 Land Erosion:
 Rivers: main source of terrigenous sed.
1. Mountains rise via plate convergence & subduction
2. Wind & rain erode mountains
3. River to sea
4. Sediment uplifts or subducts: made into mountain again
Humans alter the sediment cycle (Ex. Dams, levees, destruction of riparian habitat
& wetlands). Results in flooding, severe damage from storms (Hurricanes,
Tsunami, etc.)
b. Biogenous Sediments: Remains of living organisms (fossilize)
 Hard structures (Shells, exoskeleton)
 Oozes (30% biogenous)
o Siliceous (Silicon): EX. Diatoms (phytoplankton)
o Calcareous (Calcium-carbonate): Ex. Foraminifera (zooplankton),
Coccolithophore (Phytoplankton)
Calcareous Ooze: Deposits of Calcium-containing shells, phytoplankton
Not found below 4,500 m (14,800 ft.)
Calcium carbonate compensation depth (CCCD): Calcium carbonate dissolves in
seawater below 4,500 m: as pressure increases & temperature decreases.
Cold, deep water is acidic & High in CO2
Siliceous Ooze: Deposits of Silica-containing organisms
Common at greater depth & colder seas
Diatom ooze – Antarctica (cold, nutrient-rich, upwelling)
Radiolarian ooze
- Equatorial (Radiolarian = amoeba-like protozoans)
c. Hydrogenous Sediments: Dissolved minerals precipitated from seawater (fall out
of solution)
 Mineral sources: rock, sediment, hydrothermal vents, land erosion
o Evaporites - form in isolated seas with high evaporation [Ex. Gypsum
(CaSO4), Salt (NaCl)]
o Authigenic – formed in place
 Manganese Nodules: form via slow chemical reactions (bacteria
may aid)
 Grow 1-10 mm (0.04-0.4”) / million years!
 Compositon: Manganese & iron (50%), cobalt, nickel, copper,
often have shark tooth, algae, nuclei
 Form at depths:
 Pacific seafloor 30-50 % cover of Manganese nodules
d. Cosmongeous Sediments: Interplanetary dust: debris (comets, collisions) falls into
Earth’s atmosphere (constant)
 Most dissolves in seawater
 Minor sediment in ocean
 Impacts by large asteroids & comets: Crust thrown into space, melts, falls
back to Earth – forms microtektites (Glass-like, 0.2-0.8mm)
Classifying Sediments (cont):
4. Distribution: 3 Categories
a. Neritic sediments: Continental shelf
 Terrigenous, Current or wave deposited , Coarse grain, Rapid accumulation
b. Hemi-pelagic sediments: outer shelf & slopes
c. Pelagic sediments: deep sea
 Mixed, but greater proportion is Biogenous, Deposited suspension, Fine
grained (finest on floor), Slow accumulation
Terrigenous sediment: Not carried far out to sea
Result: Pelagic sediment dominated by biogenous material