This is a text version of the notes presented in class.  Some figures of interest in your textbook are indicated here, as well.

Feel free to email the instructor (dpalmer@kent.edu) with any
comments about the format and ease of use of these online notes.

First- A Review from Tuesday-- Latitude, Longitude, Maps

Example Map Projection: Mercator
The Mercator projection is frequently used by mariners
Mercator projections distort distance and area near the poles
 

 Example Map Projection: Equal Area
Equal area projections retain relative sizes of land masses
Linear paths between points are distorted (particularly near the edges of the map)

 Latitude and Longitude
Latitude: North-South,  Range=90°N to 90°S, North Pole=90°N, South Pole=90°S
Longitude: East-West, Range=0°E-360°E or or 180°W-180°E, 0°=Greenwich England
Latitude and longitude uniquely specify the location of each place on Earth
Kent, Ohio=41.15°N, 278.64°E
 

The Ocean Floor
In this lecture, we will cover information about the followingaspects of the ocean floor:

I.  Distinctive features of the ocean floor
• Continental shelves, slopes and rises
• Abyssal plains
• Mid-ocean ridge
• Trenches
• Guyots and Seamounts

and

II.Sediments on the ocean floor
• Terrigenous – Terrestrial sources
• Biogenic- Biological sources
• Authigenic-Precipitated out of the water
• Cosmogenic-dust and debris from space

I.  The Ocean Floor
1.  Ocean basins - large expanses of open ocean
Marginal seas - smaller saltwater regions connected to ocean basins by narrow passages
There are many marginal seas (e.g., Mediterranean, Norwegian, Caribbean)

2.  Bathymetry - Measuring Ocean Depths
Bathymetry can be measured using:
- weighted lines
- sound (acoustics)
- Earth-orbiting satellites (new!)
Acoustic bathymetry:
- a sound pulse is sent to the seafloor
- measure time needed for the echo to be received
- this time is related to the distance to the seafloor

3. Features of an Ocean Basin
 continental margins:  shelves, slopes, rises
 abyssal plains
 mid ocean ridges
 trenches
 submarine canyons and deep sea fans
 guyots and seamounts

4. Parts of a Continental Margin
Shelf - submerged area adjacent to continent
Slope - transition between continental shelf and deep sea floor
Rise - area at the base of the continental shelf covered by sediment deposited from the shelf

5. Continental Shelves
- Seaward extension of continental material
- Contain much of the sea's mineral and oil deposits and home to most economically important sea life
 
In general, continental shelves are more biologically active than ocean basins

6. A Real Continental Margin
Continental margins are not the same everywhere:
  - shelf width varies from place to place
  - slope angle varies from place to place
  - large-features are found on some margins

7. Submarine Canyons and Deep Sea Fans
Submarine canyons cut through the continental shelf and slope
- Carved by catastrophic events (turbidity currents) that carry sediment from the continental slope to
the deep sea and deposits it in a deep sea fan

8. Mid-Ocean Ridges
- Submerged mountain chains circle the Earth
- Most rise about 2 kilometers above the ocean floor
- Seismically active regions (sites of many earthquakes)

9. Abyssal Plains
Are expansive, flat areas of the deep oceans
These are some of the flattest features on the planet

10. Ocean Trenches
Are 3-6 km deeper than surrounding ocean
Geologically active (sites of  very large earthquakes and tsunami)

11.  Guyots and Seamounts
Guyots – flat topped, submerged, inactive volcanos
Seamounts – isolated volcanic peaks that rise at least 1,000 feet above the sea floor

For a good figure showing Global Seafloor Topography

II.  Sediments on the sea floor:  Different kinds of sediment are found in different parts of the ocean.  These types can be grouped into
 Terrigenous-sediment coming from the continents & islands
 Biogenic-organically produced material, like shell material, made by organisms
 Authigenic-minerals precipitating out of the water column and settling out
 Cosmogenic-dust and small particles, like tektites, reaching Earth from space

1. Terrigenous Sediments
Origin = continents and islands
- erosion of land
- volcanic ash
- wind-blown dust
Transport = rivers and wind

2. Biogenic Sediments
Origin = biology (shells and skeletons of marine organisms)
- abundant where biological productivity is high
- organic molecules in these materials can form oil and natural gas deposits

3. Authigenic and Cosmogenic Sediments
Authigenic - dissolved minerals present  in seawater chemically react to form solids
Example:  Manganese nodules
Cosmogenic - material from outer space
Example: Interplanetary dust
Authigenic and cosmogenic sediments are rare

4. Influence of Water Depth on Sedimentation
Shallow continental margins are terrigenous
Mid-depth waters far from coasts are biogenic
Deep ocean basins have red clays and authigenic nodules
- Calcium-based biogenic sediments dissolve in the deep ocean, leaving the small terrigenous
  clay particles that have traveled far from land

5. Sediment Thickness
Thick sediments near continental shelves - terrigenous and biogenic input
Thin sediments in deep regions - little terrigenous input, little biogenic accumulation
Very thin sediments near mid-ocean ridges - young seafloor

6. Global Distribution of Sedimentary Deposits

 

8. Preview of Next Lecture – Plate Tectonics & the Dynamic Earth
Focus Question:  What is the significance of ocean trenches and mid-ocean ridges?