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sediment = material composed of particles that have settled to the bottom of a liquid

boring you say?

200 million years of Earth's 4.6 billion year history are in marine sediments - not too shabby!

Information Highway to the Past

movements of the ocean floor

ocean circulation patterns

nutrient supplies for plants & animals

Deep Ocean Sediments

-- lithogenous or terrigenous

-- red brown or buff - oxidized iron

-- derived from continents, carried by winds and currents

-- ACCUMULATES slooooowly at 1 mm per 1000 years

ooze = 30% or more skeletal material by weight

-- biogenous

Oozes

-- foraminifera (protozoan or 1-celled critter)

1 micron (uM) = 1 millionith of a meter!

-- coccoliths (algae)

Carbon Crucial to Life - Overhead

More Oozes

-- diatoms (algae)

-- radiolaria (protozoans)

World Distribution of Oceanic Sediments - Fig. 4-16a,b in text

Rate of Accumulation for Oozes

-- reproduction of planktonic organisms

Destruction

-- dissolving in water

-- silica dissolved at all depths

-- calcium carbonate varies with depth

-- lots of CaCO3 in warm surface waters

-- CaCO3 dissolved at depth - more CO2

Carbonate Compensation Depth -- where CaCO3 is dissolved as fast as it falls from above -- varies from ~6000 m in Atlantic to ~3500 m in Pacific

Carbonate Compensation Depth - Fig. 4-17 in text

Coastal waters are often highly productive, with abundant planktonic organisms thriving in the surface waters. Why then are biogenous oozes rarely found nearshore??

biogenous sediments dissolve readily at shallow depths on the continental shelf?

plankton species in coastal waters have no skeletons?

planktonic organisms are consumed by large organisms, preventing deposition of skeletons?

Answer is: the large input of terrigenous sediment to the continental margin overwhelms the biogenous component in the sediment

This is tied to. . .

-- oozes can't form because they are diluted by sediments of other origins-- near continents especially

-- in areas where there is not much productivity in the surface waters

-- where the seafloor is extremely deep

so lithogenous clays may prevail or . . .

Another Type of Sediment

-- chemical reaction w/seawater causes minerals to precipitate

-- manganese nodules (first discovered in 1800s by Challenger expedition)

-- made of manganese dioxide and iron oxide

Manganese Nodules - Fig. 4-15 in text

Economic Issues

manganese, iron, perhaps copper, nickel, and cobalt

-- depressed metals market now

-- issue who owns the nodules? Law of the Sea in international waters

petroleum

-- enough oil available until 2020 - offshore drilling will still be important

-- Gulf of Mexico, Persian Gulf, North Sea

burial of nuclear waste in sediments

Ocean Drilling Program Show-and-Tell: drillbit

Last update: April 14, 2000
http://dusk.geo.orst.edu/oceans/lec09H.html