TOPIC 4 - THE EARTH'S OCEAN BASINS [Lecture ppt | pdf]


Key Questions for Geological Oceanography

What is the structure (size, shape) of each of the major ocean basins?

How did these basins form?

Do (& did) these ocean basins changes their structure?

Measuring the Size and Shape of the Earth's Ocean Basins

We want to know geographic position and water depth everywhere.

The HMS Challenger Expedition made the first attempt to measure water depth with winches and cables.

The Meteor Expedition was the frist to measure water depth with acoustic methods - Echo Sounding.

The first public map of the North Atlantic Ocean basin was published by Bruce Heezen (LDGO) in 1959.

Major Features of the Ocean Floor - I

Continental Margins:

Continental Shelf (<150 m water depth).

Continental Slope (steep ramp).

Continental Rise (sediment wedge).

all of these are cut by submarine canyons.

Types of Margins:

Passive - shelf hundreds of km wide.

Active - shelf may be less than 1 km wide (faulting, eqs., volcanoes usually present).

Major Features of the Ocean Floor - II.

Deep Ocean Basins (>4000 m water depth):

typically flat or subdued topography.

regularly cut by long fracture zones.

Mid Ocean Ridges:

long linear mountain chains.

occur in all oceans and bound basins.

fracture zones are perpendicular to ridges.

Major Features of the Ocean Floor - III.


long linear troughs.

usually occur along margins of continents.

Ocean Rises:

seamounts (guyots, atolls - all forms of submarine volcanoes).

submarine plateaus.



Return to Table of Contents