Upload
lillian-western
View
226
Download
9
Tags:
Embed Size (px)
Citation preview
Sea Floor & Sediments
Measuring the Depths Soundings
Echo Sounder
Measuring the Depths
Modern Tools ROV’s LADS Side-scan Sonar Satellites
Sea Floor Bathymetry
Continental Margin
Active margin Leading margin Pacific-type Convergent
boundary Continental shelf is
narrow and irregular
Continental Margin
Passive margin Trailing margin Atlantic-type Divergent
boundary Sediment build-up
on shelf
Continental Shelf
Continental Shelf
Formation
Shelf Break & Slope
Submarine Canyons
Turbidity Currents
Turbidites
Continental Rise
Atlantic, Indian, and Antarctic Oceans
Not usually found at active margins
Ocean Basin Floor
Abyssal Hills & Seamounts
Abyssal hills Most common topographic feature < 1000m
Seamounts Steep-sided volcanoes > 1000m
Abyssal Hills & Seamounts
Guyots (gee-ohs) Flat-topped seamounts
Coral Reefs
Trenches
Sediments
Rate of accumulation Distribution Source & abundance Chemical composition History
Particle Size
Particle Size
Size & shape Influences sinking rate and travel time
Particle Size
Particle aggregation Electrical attraction Fecal pellets
2200x
Location
Neritic Continental margins & islands
Pelagic Found on the deep sea floor
Location
Rates of Deposits
Neritic Sediments Highly variable
River estuaries Quiet bays
Relict Sediments
Rates of Deposit
Pelagic Sediments Slower than neritic 500-600 m
Source & Chemistry
4 sources:1. Preexisting rocks
2. Marine organisms
3. Seawater
4. Space
Lithogenous Sediments
Terrigenous sediments Fine to coarse Most common Weathering of rocks Transport by rivers,
winds, volcanoes and glaciers
Lithogenous Sediments
Terrigenous sediments Dominant neritic sediment Clear size distribution
Lithogenous Sediments
Pelagic lithogenous sediments Abyssal clay
70% clay-size particles 0.1 cm per 1000 years!
Red clay Due to oxidation of iron
Lithogenous Sediments
4 types of clay minerals:1. Chlorite
Lithogenous Sediments
4 types of clay minerals:2. Kaolinite
Lithogenous Sediments
4 types of clay minerals:3. Illite
Lithogenous Sediments
4 types of clay minerals:4. Montmorillonite
Biogenous Sediments
Fine to coarse 2nd most common Shells & skeletons CaCO3 [calcareous]
SiO3 [siliceous]
Oozes
Biogenous Sediments
Coccolithophorids Pteropods Foraminfera
Lysocline
Carbonate Compensation Depth
The depth at which the amount of calcareous material preserved falls below 20% of the total sediment
Biogenous Sediments
Diatoms Radiolarians
Hydrogenous Sediments
Derived from chemical reactions in the water
Hydrogenous Sediments
Carbonates Limestone-type deposits Shallow, warm water
Ooliths
Hydrogenous Sediments
Phosphorites Phosphorus in the form of phosphate Continental shelf & slope
Hydrogenous Sediments
Salts High rate of evaporation in shallow areas Carbonate salts, sulfate salts, then chlorides
Hydrogenous Sediments
Manganese nodules Manganese, iron, nickel, cobalt & copper
Cosmogenous Sediments
Sediments derived from space
Lithification
Formation of sedimentary rock Temps <200ºC
Diagenesis
Chemical changes of sediments when they react with seawater
Sampling Methods
Dredges Large bulk samples Benthic organisms
Sampling Methods
Grab samplers Mud & sand Quantitative sampling
Sampling Methods
Corers Gravity corer 1-2 m cores
Sampling Methods
Corers Piston corer Up to 20 m cores
Sampling Methods
Corers Box corer Large, undisturbed
samples
Door
Sampling Methods
Platform drilling JOIDES Resolution 1100 m cores
Sampling Methods
Acoustic profiling
Sediments as Historical Records
Paleoceanography Chemistry of biogenous sediments
Ratio of 18O:16O Proportion of these in skeletons reflects abundance
of isotopes in water
Seabed Resources
Sand & Gravel Annual world production = 1.2 billion metric
tons Only significant seabed mining done in the US
Seabed Resources
Phosphorite Mined to produce phosphate fertilizers Substantial source in Onslow Bay, NC
Seabed Resources
Sulfur Used for production of sulfuric acid
Seabed Resources
Coal Produced by burial of plant material in areas of
low oxygen Peat
Seabed Resources
Oil & Gas Represent >95% of
the value of all resources extracted from the sea floor
Sedimentary rocks 85-180 million years old
Seabed Resources
Gas Hydrates Combo of natural gas (CH4) and water Ice-like structure
Seabed Resources
Manganese Nodules Manganese, copper, nickel & cobalt Cobalt is of particular interest