Marine Sediments
Chap 5
video
Lithogenous/Terrigenous Sediment
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Derived from land
Origin from weathering/erosion
Mainly quartz (SiO2) – resistant to abrasion
Main constituent of continental shelf
sediment can also be found in deep ocean
Sediment Texture
Big, cars go so slow, cool
Sediment Erosion, Transportation,
Deposition
Sediment Maturity
Neretic Deposits
(near shore lithogenous)
• found along continental margins and islands –
mainly lithogenous
• Beach deposits – mainly quartz rich sands – but
what ever is available
• Continental Shelf deposits – carried by rivers
• Turbidite deposits due to underwater avalanches
– from turbidity currents –show graded bedding
• Glacial Deposits – grinding by ice and trapped in
glacial ice
Pelagic Deposits
(open water lithogenous)
• Fine grained material that accumulates on the
ocean floor.
• Abyssal Clay >70% clay sized particles from
continent- due to lack of other particles
• Contain oxidized iron making them red-brown
or buff
Biogenous Sediment
• Derived from hard parts of once-living
organisms – algae and protozoans.
• Macroscopic can be seen with eyes
• Microscopic too small to be seen with unaided
eye
• Microscopic organisms produce small shells
called tests and accumulates in the deep
ocean to form ooze.
Composition
• Calcium Carbonate - CaCO3 (makes mineral
calcite)
• Silica SiO2.
Calcium Carbonate forms Calcareous Ooze
• Foraminiferans are protozoans
with porous CaCO3shells .
• Coccolithophores are microalgae
that are 10-100 times smaller
than diatoms, they are called
nanoplankton. They have CaCO3
plates (cocoliths) that make up
their shell. These decompose to
form cocolith-rich CaCO3 ooze
that can later lithify to form
chalk and limestone.
Dover
Stromatolites
• Lobate structures made of
layers of carbonate from
cyanobacteria at
particular shallow depth.
Silica forms Siliceous Ooze
• Silica biogenous ooze made
mainly from planktonic algae
called diatoms and a protozoans
called radiolarians
• Diatomaceous earth used in
filters, abrasives, absorbents,
glass. Also diatoms have a
droplet of oil in them that have
accumulated into petroleum
deposits (ex: off California)
• Silica dissolves is seawater and
will only accumulate silica ooze
where there is high production.
Calcite Compensation Depth -CCD
CaCO3 is saturate in warm shallow
waters and can form sediments.
At deeper cooler waters CaCO3 is
not saturated so does not form
deposits after a certain depth –
CCD.
Average CCD is 4500 m
Below 5000 m, calcareous ooze not
usually found unless it was made at
a higher depth and then covered
before it’s present depth.
lysocline
Hydrogenous Sediment
• Derived from seawater
• Chemical reaction cause minerals to
precipitate out of sea water usually when
there is a temperature or pressure change
Manganese nodules
• 5-20 cm lumps of Mn, Fe and other metals
• Found on deep ocean floor 100/m2
Phosphates
• Phosphate bearing compounds found on rocks
and nodules on the continental shelf and
banks at depths < 1000m.
• Used as fertilizer and other agricultural
proposes
Carbonates
• Aragonite and calcite are the two most
important carbonate sediments
• Aragonite has a different crystalline
structure and is less stable and changes
into calcite over time.
• Biogenous in origin, aragonite crstals can
form hydrogenously by precipitating
directly from seawater.
• Oolites are small calcite spheres that form
in shallow tropical waters with high
CaCO3 concentrations.
Metal Sulfides
• Made by black smokers at hydrothermal vents
• Iron, nickel, copper, zinc, silver and other
metals.
Evaporites minerals
• In restricted circulation areas where
evaporation is high – seawater becomes
saturated with minerals and the minerals
precipitate out.
• Collectively called salts, some evaporites may
taste salty because of NaCl and other do not
like calcium sulfate minerals anhydrite (CaSO4)
amd gypsum (and H20)
Cosmogenous Sediment
• Extraterrestrial origin
• Spherules = microscopic, usually once molten
basalt from impact events, forms tektites
• Although 90% of tektites are destroyed by
frictional heating with the atmosphere,
300,000 metric tons/year reach Earth
• Meteor = macroscopic, impact material made
of rock (chondrites) or iron and nickel (irons)
settle out around impact sites.
% of Pelagic Sediments
• 47.7% Carbonate
• 14.2% Siliceous
• 38.1% Abyssal