Transcript Geological Provinces of the Ocean III

Most of the organisms that produce biogenous sediments are
microscopic and are therefore called microfossils.
These microfossils serve as a historical record of organisms that lived in
the ocean and give clues about marine conditions during their life.
Performing carbon dating, the age of microfossils can be determined.
Carbon dating = ratios of different isotopes of carbon are
measured.
Ratios of different isotopes of oxygen, strontium, or calcium can
determine historical water temp.
Ice cores and air bubbles in ice can give more information about the
earths past climate.
Climate and Changes in Sea Level
ICE AGE
long cold periods
Large amounts of water is trapped on land as glaciers and
therefore sea level drops.
Interglacial Periods
brief warm periods like the one we are in now
The peak of the last ice age occurred 18,000 years ago.
- ice sheets 2mi. thick covered N. America
- Sea level was about 425ft. lower than today
The greenhouse effect and other human influences can possibly
prevent the next ice age from occurring.
The Geological Provinces of the Ocean
The sea floor is divided into two
main regions:
1) continental margins
2) deep sea floor
Continental Margins
The offshore zone separates the dry-land portion of a continent from the deep ocean
floor. It consists of:
1) continental shelf
2) continental slope
3) continental rise
Characteristics of the Continental Shelf
•
shallow
•
closest part to land.
•
part of the continent that
presently happens to be
under water.
•
only 8% of ocean’s surface
area.
•
biologically rich.
•
include submarine canyons.
•
the outer edge is called the shelf break.
It’s where the slope gets steeper. Usually
at about (400-600ft. deep)
Characteristics of the Continental Slope
• steepest part of the continental margin.
• the edge of the continent.
• submarine canyons that began on the shelf continue down the slope.
• canyons carry sediment from the shelf to the deep sea floor where it forms the
continental rise.
Characteristics of the Continental Rise
• thick layer of sediment at the base of the slope.
• can originate from deep sea canyons forming a deep sea fan.
• can originate from currents that have redistributed the sediment from deep sea fans.
Characteristics of the Abyssal Plain
• The sea floor
• Biologically rich.
• Almost flat
• Rises toward mid-ocean ridge (at less than one degree)
• Associated with seamounts, guyots, plateaus,and rises.
• Slopes steeply downward at trenches.
Active and Passive Margins
Active Margin
• continental crust (South American Plate) is colliding with oceanic
crust plate (the Nazca Plate) to form a trench.
• earthquakes and volcanoes are associated with trenches.
• features consist of steep rock shorelines, little or no shelf, a steep slope, and no rise.
Passive Margin
• edge left when South America separated from Africa.
• features consist of a flat coastal plain, wide shelf, a gentle slope, and thick rise.
Mid-Ocean Ridge
• Includes a central rift valley.
• Associated with hydrothermal vents and deep hot springs.
The formation of hydrothermal vents and deep hot springs occurs as
follows:
1) Seawater seeps down through cracks.
2) Seawater gets heated by the mantle.
3) Heated water (50-660° F) forces its way back up through the crust.
The hot water can dissolve a variety of sulfides.
When the hot water mixes with the surrounding sea water it cools and
the dissolved minerals solidify and accumulate around the vents
forming Black Smokers.