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Sea Floor & Sediments
Measuring the Depths Soundings
Echo Sounder
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Measuring the Depths
Modern Tools ROV’s LADS Side-scan Sonar Satellites
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Sea Floor Bathymetry
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Continental Margin
Active margin Leading margin Pacific-type Convergent
boundary Continental shelf is
narrow and irregular
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Continental Margin
Passive margin Trailing margin Atlantic-type Divergent
boundary Sediment build-up
on shelf
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Continental Shelf
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Continental Shelf
Formation
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Shelf Break & Slope
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Submarine Canyons
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Turbidity Currents
Turbidites
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Continental Rise
Atlantic, Indian, and Antarctic Oceans
Not usually found at active margins
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Ocean Basin Floor
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Abyssal Hills & Seamounts
Abyssal hills Most common topographic feature < 1000m
Seamounts Steep-sided volcanoes > 1000m
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Abyssal Hills & Seamounts
Guyots (gee-ohs) Flat-topped seamounts
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Coral Reefs
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Trenches
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Sediments
Rate of accumulation Distribution Source & abundance Chemical composition History
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Particle Size
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Particle Size
Size & shape Influences sinking rate and travel time
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Particle Size
Particle aggregation Electrical attraction Fecal pellets
2200x
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Location
Neritic Continental margins & islands
Pelagic Found on the deep sea floor
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Location
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Rates of Deposits
Neritic Sediments Highly variable
River estuaries Quiet bays
Relict Sediments
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Rates of Deposit
Pelagic Sediments Slower than neritic 500-600 m
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Source & Chemistry
4 sources:1. Preexisting rocks
2. Marine organisms
3. Seawater
4. Space
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Lithogenous Sediments
Terrigenous sediments Fine to coarse Most common Weathering of rocks Transport by rivers,
winds, volcanoes and glaciers
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Lithogenous Sediments
Terrigenous sediments Dominant neritic sediment Clear size distribution
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Lithogenous Sediments
Pelagic lithogenous sediments Abyssal clay
70% clay-size particles 0.1 cm per 1000 years!
Red clay Due to oxidation of iron
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Lithogenous Sediments
4 types of clay minerals:1. Chlorite
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Lithogenous Sediments
4 types of clay minerals:2. Kaolinite
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Lithogenous Sediments
4 types of clay minerals:3. Illite
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Lithogenous Sediments
4 types of clay minerals:4. Montmorillonite
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Biogenous Sediments
Fine to coarse 2nd most common Shells & skeletons CaCO3 [calcareous]
SiO3 [siliceous]
Oozes
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Biogenous Sediments
Coccolithophorids Pteropods Foraminfera
Lysocline
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Carbonate Compensation Depth
The depth at which the amount of calcareous material preserved falls below 20% of the total sediment
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Biogenous Sediments
Diatoms Radiolarians
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Hydrogenous Sediments
Derived from chemical reactions in the water
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Hydrogenous Sediments
Carbonates Limestone-type deposits Shallow, warm water
Ooliths
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Hydrogenous Sediments
Phosphorites Phosphorus in the form of phosphate Continental shelf & slope
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Hydrogenous Sediments
Salts High rate of evaporation in shallow areas Carbonate salts, sulfate salts, then chlorides
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Hydrogenous Sediments
Manganese nodules Manganese, iron, nickel, cobalt & copper
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Cosmogenous Sediments
Sediments derived from space
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Lithification
Formation of sedimentary rock Temps <200ºC
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Diagenesis
Chemical changes of sediments when they react with seawater
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Sampling Methods
Dredges Large bulk samples Benthic organisms
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Sampling Methods
Grab samplers Mud & sand Quantitative sampling
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Sampling Methods
Corers Gravity corer 1-2 m cores
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Sampling Methods
Corers Piston corer Up to 20 m cores
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Sampling Methods
Corers Box corer Large, undisturbed
samples
Door
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Sampling Methods
Platform drilling JOIDES Resolution 1100 m cores
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Sampling Methods
Acoustic profiling
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Sediments as Historical Records
Paleoceanography Chemistry of biogenous sediments
Ratio of 18O:16O Proportion of these in skeletons reflects abundance
of isotopes in water
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Seabed Resources
Sand & Gravel Annual world production = 1.2 billion metric
tons Only significant seabed mining done in the US
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Seabed Resources
Phosphorite Mined to produce phosphate fertilizers Substantial source in Onslow Bay, NC
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Seabed Resources
Sulfur Used for production of sulfuric acid
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Seabed Resources
Coal Produced by burial of plant material in areas of
low oxygen Peat
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Seabed Resources
Oil & Gas Represent >95% of
the value of all resources extracted from the sea floor
Sedimentary rocks 85-180 million years old
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Seabed Resources
Gas Hydrates Combo of natural gas (CH4) and water Ice-like structure
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Seabed Resources
Manganese Nodules Manganese, copper, nickel & cobalt Cobalt is of particular interest