Sea Floor and Sediments

G131 HOME

INFORMATION

SCHEDULE

RESOURCES

EXERCISES

NOTES Links to summaries of key issues for each topic

PREAMBLE

Introduction

History

PART I

Water Planet

Plate Tectonics

Sea Floor

Review 1

Physical Prop.

Chemistry

Ocean Stuct.

PART II

Atmosphere

Currents

Waves

Tides

PART III

Coasts/Beaches

Environ. for Life

Production

Plankton

Nekton

Benthos

Environ. Issues

VISUALS

Links to images employed in lectures on a topic-by-topic basis

TEXT Link to chapter outlines at online learning center at McGraw Hill.

NOTES Links to summaries of key issues for each topic

Sea Floor and Sediments (contd.)

Notes on Topic:

The notes represent summaries of key issues for each topic

They emphasize the terminology used to describe the various phenomena.

4. Patterns of Deposits:

Learning Objectives:

Controls on patterns of sediment deposition.
Sources, sinks and controls on glacial sediments and wind-blown dusts.
Factors affecting particle sizes, sorting, graded bedding, rates of deposition.

Sites of Deposition:

Terrigenous:

derived from land, deposited close to source

Neritic:

shallow-water, coastal sediments from mixed sources (land, biota)

Pelagic:

deep sea sediments

Terrigenous Deposits:

River transport

major source for sediments in ocean (13 x 10⁹ tons/a),
most from mountainous areas, especially Asia
deposition controlled by physical processes,
sinking controlled by size
larger particles deposited near land
fine-grained material reaches deep ocean
turbidity current redistribute shelf sediments
dilute biogenous materials

Glacial transport

rock debris and flour (scoured and powdered rocks)
rafted over ocean (ice-rafted debris) by icebergs
form glacial-marine deposits

Wind-blown transport

dusts, silt, loess blown by winds, varies seasonally

Particle Size and Rates of Deposition:

Particle size variation:

gravel (>2mm), sand, silt, clay
may be poorly sorted (mixed) or well sorted
settling rate dependent on size
particles may aggregate or settle faster in fecal pellets

Rate of sediment accumulation:

deep ocean 0.5 - 1 cm/ka
up to 8m/a by major rivers

Formation of Rock:

Loose sediments are transformed by burial and heat
Lithified into sedimentary rocks
Extensive increases in temperature and pressure create metamorphic rocks

Sampling Methods:

Various dredges, grab-samplers retrieve ocean sediments

coring devices collect sediment sequences
drill ships maintain dynamic position and retrieve cores
sediment layers probed by acoustic profiling

5. Seabed Deposits:

Learning Objectives:

Recognition of diversity of material resources on sea floor.
Need for international agreements in the use or explotiation.

Types:

Many different resources, but few economically viable.
Sand and Gravel:

mined in shallow waters
coral sands as source of calcium carbonate
in some areas recovery of ore minerals,: tin, gold.

Phosphorite:

Phosphorite sands and muds in shallow waters
potential source of fertilizer

Sulfur:

mined in Gulf of Mexico by superheated steam.

Coal:

undersea coal deposits, originally formed on land
mined off Japan

Oil and Gas:

offshore production requires deep-drilling capability
many deep-water prospects on Atlantic margins

Manganese nodules:

source of metals, exploration, not commercial exploitation

Sulfide Minerals:

hydrothermal vent deposits as sources of metals

Laws & Treaties:

Territorial Waters:

6km, to 22km (UN, 1982)

Exclusive Economic Zone to 370km
Conference on the Law of the Sea in 1974:

treaty completed in 1982
ocean resources heritage of all humankind,
convention effective 1994, now endorsed by US.

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