10/27/15 Marine Sediments
Lithogenous Sediments
Marine Sediment Classification
Sources of lithogenous sediments
: Broken rocks from continents, islands, coastal
areas; or from volcanic ash
Classified by origin
•  Lithogenous (Terrigenous) – derived from land
•  Biogenous (Biogenic)– derived from organisms
•  Produced by weathering
•  Hydrogenous (Authigenic) – derived from water
: Breaking of rocks into
smaller pieces.
•  Cosmogenous (Cosmogenic) – derived from outer space
•  Mechanical weathering
•  Chemical weathering
Mechanical Weathering Frost wedging
Pressure release (exfoliation)
Chemical Weathering
Decomposition of rocks by chemical agents
React with acid
Lithogenous Sediments
Sediments eroded and
transported to the ocean
Oxidation
Transporting agents
•  Streams
•  Wind
•  Glaciers
•  Landslides
Abrasion
Lithogenous Sediments: Texture and Environment
Texture: size and shape of particles
Grain Size: reflects energy of transportation
e.g.,
e.g.,
Silicate minerals + H+ à quartz +
CaCO
+ H2CO
3(Calcite)
3 clay
minerals
+ dissolved
cations
2++, Fe
-)
2+ etc.)
(K+,
Ca+2+2
, Mg
--->Na+,
Ca +2
(HCO
e.g.,
4 (Fe3O4 (magnetite) + O2
----> 6 (Fe2O3) (hematite)
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Lithogenous Sediments: Texture- size -Sorting
Measure of grain size uniformity
•  indicates selectivity of
transport agent
Lithogenous Sediments: Texture- Shape (rounding)
Reflect distance and agent of
transportation process
•  Rounded
•  Angular
•  Well-sorted – all same size
•  Poorly sorted – different size
particles mixed together
Conglomerate Breccia
1 10/27/15 Biogenous Sediments
: Hard remains of once-living organisms Macroscopic biogenous sediments – include visible
shells, bones, teeth of once-living large organism
e.g., Fossiliferous limestone
Silica-rich microscopic Biogenous Sediments
Biogenous Sediments
Microscopic Biogenous Sediments
Silica-rich •  Diatoms
–  single-cell algae
–  Photosynthetic
–  mostly planktonic
Microscopic Biogenic Sediments
Calcium Carbonate
•  Coccolithophores
–  Also called
nannoplankton
–  Photosynthetic algae
•  Foraminifera
–  Protozoans
–  not photosynthetic,
need external food
•  Radiolarians
–  single-cell Protozoans
–  generally not photosynthetic,
need external food
–  also planktonic
Hydrogenous Marine Sediments
Calcium Carbonate Biogenic Sediments
Lithified coccolith-rich ooze: Rock chalk
•  Tests – shells of
microscopic organisms
•  Minerals precipitate directly from seawater
due to changes in T, P, chemical composition
e.g.,
•  Sediments rich in tests
are called ooze
e.g.,
siliceous ooze.
calcareous ooze
–  Carbonates
–  Phosphates
–  Evaporites
–  Manganese nodules
The White Cliffs of Dover,
Southern England
Hydrogenous Marine Sediments –  Metal sulfide
Age: Cretaceous Period
Hydrogenous Marine Sediments Hydrogenous Marine Sediments
Carbonates
e.g., Calcite, Aragonite, Oolites
Phosphates
•  Phosphorus-bearing
•  Occur in ocean of very
high biological
productivity
Evaporites
e.g.,
Halite (rock salt) NaCl
Gypsum CaSO4·2H2O
When lithified à Limestone
2 10/27/15 Hydrogenous Marine Sediments
Manganese Nodules
•  Manganese, iron, and other metals
Hydrogenous Marine Sediments
Cosmogenous Marine Sediments
Metal Sulfides: Contain Iron, Copper, Zinc, Silver + Other metals.
•  Macroscopic meteor debris
•  Microscopic iron-nickel and silicate spherules (small
globular masses)
–  Tektites
–  Space dust
Tektites
Marine Sediment Distribution
Neritic – Shallow water deposits
Pelagic - Deeper-water deposits
Neritic Biogenic Sediments Reef: in warm shallow water
Space dust
Neritic Biogenic Sediments
Stromatolites
•  Layered carbonate structures formed in high salinity, warm,
shallow seawater
•  Cyanobacteria produce these deposits by the trapping,
binding and cementation of fine sediments in mucous mats
Neritic sediments: Mostly lithogenous
•  Beach deposits: Mainly quartz-rich sands
•  Continental shelf deposits: Relict sediments
•  Bottom of continental slope: Turbidite deposits
•  Glacial deposits: High-latitude continental shelf;
currently forming by ice rafting
+ Some biogenic & hydrogenous
Neritic Carbonate Deposits
Precambrian Stromatolites
Coquina (near beach)
Fossiliferrous Limestone
(CaCO3)
Neritic Hydrogenous Deposits
Oolitic Limestone
e.g., Stromatolites near Shark Bay, Australia
Marine Sediment Distribution
Pelagic sediments
Abyssal Clay
At least 70% clay sized
particles from continents
e.g.,
volcanic ash
wind-blown dust
Oldest known fossils
: Stromatolites
Red from oxidized iron
Wind Transported Lithogenous sediments 3 10/27/15 Marine Sediment Distribution
Pelagic Deposits - Microscopic Biogeneous sediments Siliceous ooz (e.g., tests of diatoms & radiolarians)
•  Seawater is under-saturated with silica at all depths
•  Accumulates in areas of high productivity
•  Silica tests no longer dissolved by seawater when
buried by other tests
Distribution of Pelagic Biogenous Sediments
Calcareous Ooze
CCD: Calcite compensation depth
e.g, tests of cocoliths & Foraminifera
•  Warm, shallow ocean saturated with
calcium carbonate
•  Cool, deep ocean undersaturated
with calcium carbonate
CCD: Calcite compensation depth
•  Rate of supply = rate at which the
shells dissolve
•  Below CCD:
CaCO3 readily dissolves
Microscopic tests sink slowly from surface ocean to
sea floor (10–50 years)
Sea Floor Spreading and Sediment Accumulation
•  Rare calcareous ooze below 5000 meters in modern ocean
•  Ancient calcareous oozes at greater depths if moved by
sea floor spreading
Remains of cocoliths and other debris High % of calcareous ooze follow the mid-ocean ridges
Neritic and Pelagic Sediment Distribution
A 200-micrometer-long fecal pellet, large enough to sink
from surface to ocean floor in ~10-15 days.
Worldwide Marine Sediment
Thickness
•  Neritic sediments cover about ¼ of the sea floor
•  Pelagic sediments cover about ¾ of the sea floor
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