Chapter 3
The Sea Floor
and its
Sediments
Copyright © 2014 The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chapter 3 The Sea Floor and
Its Sediments
Learning outcomes
1. 
2. 
3. 
4. 
5. 
6. 
7. 
8. 
9. 
Review the evolution of methods to measure ocean depth with
time up to the present
Construct a simple cross section of an ocean basin including both
a passive and active continental margin
Discuss the formation of atolls
Sketch the location of ocean ridges and trenches
Explain three different ways to classify sediments
List the organisms that contribute the majority of calcareous and
siliceous sedimentary particles
Identify where biogenous and lithogenous sediments are dominant
on the sea floor
Define isotopes and describe how they can be used with marine
sediments as historical records
List multiple seabed resources and appraise the extent to which
they are currently being recovered
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Section 3.1
Measuring the Depths
Copyright © 2014 The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Methods of Measuring Depth
•  Greek geographer Posidonius used a large rock
attached to a rope
•  Hand line and wire marked with fathoms, with a
lead weight on the end
•  In deep water, lines and weights could take
hours to reach the bottom
–  By 1895:
•  ~7000 measurements deeper than 2000 m had been made
•  ~550 measurements deeper than 9000 m had been made
•  Echo sounder, or depth recorder
•  Satellites that measure sea surface elevation
4
Echo Sounder, or
Precision Depth Recorder (PDR)
5
Using Sound to Map the Seafloor
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Sea Surface Elevation
used to Map the Seafloor
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Section 3.2
Seafloor Provinces
Copyright © 2014 The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Generalized Ocean Basin Cross Section
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Passive Continental Margin
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Submarine Canyons
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Abyssal Plains
•  The deep sea floor between 4000 and
6000 m depth
•  Cover roughly 30% of Earth’s surface
•  Common features
–  Islands
–  Seamounts (> 1 km tall)
–  Abyssal hills (< 1 km tall)
–  Guyots (flat top, once was an island)
–  Coral reefs
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Coral Reefs
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Ocean Ridges and Rises
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Ocean Trenches
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Section 3.3
Sediments
Copyright © 2014 The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Why Study Marine Sediments?
•  Provide information about Earth and its
environmental systems on long time scales
•  Can provide information about past climate
change
•  Can provide information about seafloor habitats
and how they impact marine organisms
•  Locating offshore mineral resources
•  Map offshore pollution
•  Identify sites for coastal structures and oil
platforms
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How Marine Sediments are Studied
Recovering sediment cores
Dredging the seafloor
Seismic imaging
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Classifying Marine Sediments
•  Particle size
•  Location
–  Neritic
–  Pelagic
•  Source and chemistry
– 
– 
– 
– 
Lithogenous
Biogenous
Hydrogenous
Cosmogenous
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Particle Size
•  Well-sorted vs. Poorly-sorted
•  Sinking Rate and Distance Traveled
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Location
(Distance from the shore)
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Source and Chemistry
•  Source classifications
–  Lithogenous, or Terrigenous
–  Biogenous
–  Hydrogenous
–  Cosmogenous
•  Chemistry
–  Silicate, or Siliceous, SiO2
–  Carbonate, or Calcareous, CaCO3
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Global Distribution of Marine Sediments
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Lithogenous Sediments
•  Material that comes from the land
•  Transported by:
–  Wind
–  Rivers
–  Ice rafting
•  Generally derived from preexisting rocks
–  Also known as Terrigenous sediments
–  Abyssal clay, or red clay, is composed of at
least 70% by weight clay sized particles
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Biogenous Sediments
•  Derived from organisms
•  “Ooze” contains >30% biogenous
material
•  Siliceous oozes
–  Phytoplankton: diatoms
–  Zooplankton: radiolaria
•  Calcareous oozes
–  Phytoplankton: coccolithophorids
–  Snails: pteropods
–  Amoeba-like animals: foraminifera
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Dissolution of CaCO3
lysocline: dissolution begins
Carbonate compensation depth: supply = dissolution
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Variable depth of Lysocline and CCD
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Hydrogenous Sediments
• 
• 
• 
• 
• 
Derived from the water
Carbonates
Phosporites
Salts
Manganese nodules
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Cosmogenous Sediments
•  Derived from space
•  Tektites
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Section 3.4
Seabed Resources
Copyright © 2014 The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
•  Sand and gravel
–  Sand and gravel, calcium oxide, calcium carbonate,
tin, iron, platinum, gold, and diamonds
•  Phosphorite
–  Phosphate fertilizer
•  Oil and gas
•  Gas hydrates
–  Methane and water
•  Manganese nodules
–  Manganese, copper, nickel, and cobalt
•  Sulfide mineral deposits
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Summary
• 
• 
Methods for measuring ocean depth
Bathymetric features
– 
– 
– 
• 
Sediment classification
– 
• 
Size, location, origin, and chemistry
Biogenous sediments
– 
– 
• 
• 
Continental shelf, slope, and rise
Ocean basin floor
Seamounts and barrier reef formation
Siliceous and calcareous sediments
Carbonate compensation depth (CCD)
Sediment sampling methods
Calcareous biogenous sediment cores
– 
Used to study climate change
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