Oceanography - Ch 5
5(1)
(1)
Sediment Types; Classification by Size
I
A. Definition - what is sediment?
-Loose particulate material deposited or precipitated
from fluid or air
-example: grounds in a coffee cup
-When cemented, sediments become sedimentary rx
B. Types of sediments Fig 5.1-5•3
-Dependent upon physical & biological processes,
wide variety
-examples:
sand
mud
gravel
ooze
-Variables include:
-thickness (absent to +/- 7000 feet)
-color (all hues of the spectrum
-surface features (smooth vs rough)
C. Classification by size and source
1. By size - Table 5.1 (soccer, tennis, golf balls, marbles)
-Sediment generally sorted by size during transport
due to energy regime of transport medium
-High energy water moves large and small
particles lag, sand, clay. boulders in a fast
mountain stream)
-Low energy water moves only small particles
lag, sand & clay in slow-moving river)
Example- Same water velocity out of lab hose (same "energy")
Which will drop out first on the way to the sea?
Sand ?
Cobble ?
Pebble ?
5(2)
-Types of sorting
-Well-sorted grains -Energy of environment consistent;
fluctuates only slightly leg, beach or river) -Grain sizes
similar in a deposit (all finer ones continue to be carried
downstream)
-Poorly-sorted grains -Energy of environment fluctuates
considerably, from high to low energy (eg, turbidity current)
-Grain sizes dissimilar
Lee 9 Classification of Seds (cont)
1. Review classification by size Table 5.1
2. Classification by source Table 5.2
4 types
•Terrigenous "earth-generated"
•Biogenous "lice-generated"
*Hydrogenous "water-generated"
•Cosmogenous "universe-generated"
5(3)
1. Terrigenous
-derived from land
-most abundant wsed in terms of volumes deposited
-16.5 billion tons/yr dumped into sea
-primarily qtz & clay
-qtz drops out along cont margins unless carried far offshore via submarine
canyons Fig 4.9
- clay carried far offshore in suspension
-settling time to sink 2.5 mi = 50 yrs or more
2. Biogenous (life-generated)
-'oozes' derived from plants & animals
calcareous
siliceous
both from shells, skeletons of tiny animals & plants
at death, shells drop to sea floor
life most abundant nr cont margin, but drift out over deep ocean
3. Hydrogenous
minerals precip. directly from seawater
- manganese nodules
- phosphorite nodules
4. Cosmogenous
- cosmic or extraterrestrial origin
- shpaed by air drag
5(4)
Ch 5(cont) D. Distribution of Seds
2 main environments
1. Neritic region - continental shelf
2. Pelagic region - cont. slope,cont rise, deep-ocean basin
1. Neritic regions("deposits of the coast")
-predom terrigenous seds (w/some biogenous)
-particle size in general grades from coarser nearshore to finer offshore (hiqher to
lower energy)
-rate of sed depos (up to 1m/1000 yrs) >deep ocean
-seds can reach 1000s feet in thickness as they
become lithified into rock
2. Pelagic region deposits ("of the sea") -more % biogenous than on shelf (because not much
terrig sand & silt makes it out this far)
-lots sed on slope & rise, less so on basin floor
-types of pelagic deposits
Turbidites (terrigenous)
Clays (terrigenous); make up 38% of deep-sea
seds
Biogenous Oozes
-not slimy after all
slow rate of deposition
-2 main types of oozes
-calcareous (usu in warm water)
-siliceous (usu in cold water)
types of oozes (cont)
5(5)
1 Calcareous ooze (CaC03)
-48% of all deep-ocean seds are calc. ooze
-composed of calcium carbonate shells
(from little plants & animals)
-not found below 4500 m
Why? (you may ask ....)
Because below 4500 m seawater dissolves
whatever CaC03 is accumulating (due to cold temp)
Therefore, rate of accumulation = rate of dissolution
(No net gain of sediment)
Interesting feature- "snow line" on undersea mts at 4500 m, like snow line on
mts on land (good fig in book)
2. Siliceous (SiO2)
predominates in cold regions, high latitudes
(because CaC03 doesn't precipitate in cold
water)
-found at depths >4500 m (because calcareous
ooze is dissolving away)
Hydrogenous deposits (water-generated)
 Manganese nodules fig in book
 Phosphorite nodules
-both show slow growth
- in areas of little sed deposition (otherwise, would be
covered up)
 Evaporites (precipitate out of seawater as mineral concen
goes up due to evaporation)
In order of precipitation:
Calcium carbonate (calcite) 1st
Calcium sulfate (gypsum) 2nd
Sodium chloride (halite=salt) 3rd
 Oolites (or ooliths) -CaC03 coated grains due to rolling
around on the beach in swash zone