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Marine Provinces
The effect of Plate Tectonics
(Once again not a form of dubstep)
• This chapter is quite literally about the shape
of the ocean floor. It has been created over
billions of years by several processes. Perhaps
the most influential has been Plate Tectonics.
I. Methods of measuring the ocean depths =
Bathymetry.
A. Soundings – Earliest means (85BC) of
measuring ocean depth.
1. utilized a weight and rope.
2. Depth was measured in fathoms (6ft).
B. Echo soundings - Began in the early 1900s
1. Eco sounder used sound “pings”
bounced off sea floor to measure depth.
2. Accurate but not detailed.
3. Recent Radar technology is improving
C. Satellite imaging –
1. Can “see” large areas of sea floor at one
time.
2. They can cover areas not yet mapped by
ships (very slow).
3. The shape of the ocean surface itself
reflects large features on the seafloor below.
4. Typically combined with other Bathymetric
techniques as resolution from space is low.
D. Seismic Reflection Profiles
1. Low frequency explosion or gun sounds
penetrate and bounce off sediment and rock
differently.
2. This Seismic Reflection Profile shows
sediment layering (oil exploration).
II. Features of the Continental Margins
A. Ocean floor is divided into
1. Continental margins – shallow, close to
continents.
2. Deep ocean basins – Deep, further from land.
3. Mid-ocean ridge – shallow, near middle of
ocean (remember plate tectonics).
B. Continental Margins
1. Passive vs. Active continental margins.
a. Passive margins – imbedded in the interior of
lithospheric plate (not close to a boundary).
i. thick sediment accumulation.
ii. Broad continental shelf
iii. Little volcanic and earthquake
activity.
b. Active Margins – Near lithospheric boundary.
i. deep-sea trenches are common
ii. Chains of islands common
iii. Lots of volcanic and earthquake activity
iv. Thin sediment accumulation
C. Continental shelf – Generally flat zone
extending from a passive shore.
1. average width is 43 miles.
2. many sediment features and islands located
here.
D. Shelf break marks the boundary between
the continental shelf and continental slope.
E. Continental Slope – steep slope between
shelf and Abyssal plain.
a. Submarine Canyons are formed in the
slope.
i. formed by erosion and turbidity
currents.
F. Continental Rise – Pile of debris at the base
of the Continental slope.
1.Formed from many deep sea fans.
a. that is at the mouths of canyons.
2. Function of erosion.
III. Deep-Sea ocean basin features.
A. Abyssal Plains – Some of the deepest,
flattest portions of the oceans.
1. Formed by suspension settling (fine
particles) and cover ocean crust features.
2. Not many found in Pacific Ocean.
a. Trenches near shelf act as a “gutter” for
debris.
3. Volcanic peaks of abyssal plain
a. Abyssal hills are only visible in the Pacific
because they have been covered by sediment
in the other ocean basins (eg. Atlantic)
b. Sea mounts – volcanic peaks remaining
under water but rising over 1KM above sea
floor.
c. Islands – Sea mounts that rise above the
sea surface. example the Hawaiian islands.
4. Cold seeps and Methane Hydrates.
a. support unique ecosystems free from
sunlight energy.
5. Volcanic reef development.
a. First a Fringing reef develops (coral) directly
from shoreline.
b. Second. As volcanic island subsides
(erodes) deeper lagoons are formed behind
reef. Now it is a Barrier Reef.
c. Third. Coral grows above water level and
island erodes below water. It is now an Atoll.
-So first fringing reef, second barrier reef, third
atoll.
6. Tablemounts – AKA Guyouts
a. Stage of subsiding volcanic Sea Mount after
Atoll.
b. Flat-top over 200m under surface.
c. Reef (atoll) remnants remain but are too
deep to be alive.
• IV. Mid-Oceanic ridges –
A. Occupy about 30% of the ocean floor.
B. They are divergent boundaries where ocean
basins grow – High volcanic activity
1. This is an area where new lithosphere is
produced (recall convection cells)
C. Divergent are different from Convergent ocean
boundaries (deep-sea Trenches) where lithosphere is
Destroyed.
1. incidentally these trenches have some of
the steepest slopes in the ocean.
***Totally random bit of important information***
= A sediment-laden current that flows off of the
continental slope is called a turbidity current.
-As water picks up sediments on the continental
shelf they become more dense and thus flow
quickly down the continental slope after passing
over the continental breaks and thus causing
underwater avalanches that form the submarine
canyons……. There you go.
The End