MARINE PROVINCES
and features of ocean floor
If you started to walk from Santa Cruz
toward Hawaii…
What do you think would be main
driving force behind what’s on ocean
floor?
Tectonics
key factors shaping for character of
seafloor:
1. Plate Boundary types (Active vs. Passive)
2. Seafloor Spreading
3. Isostatic Equilibrum
Secondary Drivers:
1. Erosion from Coasts (affects margins)
2. Sedimentation (key everywhere)
Leads to :
Three main regions of ocean
floor:
1.
CONTINENTAL MARGINS
2.
DEEP OCEAN BASINS
3.
MID-OCEAN RIDGES
1. Continental shelves
Continental shelf
Extends from shoreline to shelf break
Gently sloping feature (tenth of a degree)
Made of continental crust
Covered with sediments
Width varies (10m-1500km) avg. = 70km
Shelf break occurs at 135 m depth (on avg)
Continental shelves
Siberian shelf = largest in world
N. Sea
Sunda shelf
Note: Wide vs. Narrow shelves tied largely to tectonics
Continental shelves
E. Siberia continental shelf: Can see it is clearly an extension
Of the continent
Continental Slope
* Lies beyond Shelf break
( Slope is steep (1-25 ˚, avg of 4˚)
* Has Submarine Canyons
Formed by ancient rivers and/ or “turbidity” currents
1)Ancient Rivers: during last ice age rivers carved the
submarine canyons during times of low sea level
(120m lower!).
* Many (but not all) canyons are situated at the mouths
of rivers.
Salinas River
Carmel River
Continental shelves: importance of
glacial cycles
Global Sea level Fluctuation – Glacial / interglacial cycles.
How to read a chart.
2) Turbidity currents
Huge undersea avalanches that
carve out the canyon
Figure 3-8a
Examples of
“Turbidites” that
have been uplifted
and exposed on land
At Point Lobos, CA.
SIO Canyon
SIO Canyon Rim
SIO Canyon Rim
Turbidity Flows
Turbidity movies:
http://learningobjects.wesleyan.edu/turbiditycurrents/
Monterey Canyon Turbidity Flow
Caught in the Act...again!
December 17-19, 2002
MBARI scientists observed two events in
Dec 2002 alone..
Turbidity Currents
Turbidity current reprise
~45- 50 mph!
Continental Rise
“RISE”
Cont Rise
Turbidity flows create:
Canyons & Deep sea Fans
Fans
2. Active vs. Passive margins
What accounts for a margin
being
“Active” vs. “Passive”?
Active Margins:
continental margins
at a convergent
plate boundary
Passive Margins:
continent margins
are in middle of plate
Figure 2-13a
Examine the shelf width
on active margins (West
coast of North and South
America)
VS.
passive margins (East
coast of North and South
America)
Active “convergent” margin
features
Steep Slope
Deep Trench
Coastal
Mountains
Narrow shelf
(or none)
(often
volcanic)
“transform” active margin
many features similar to “convergent’ – but
no subduction so…
1. Relatively narrow shelf
2. Steep slope- but No Trench
3. Submarine canyons/ fans on the
rise
1. California = transform active
margin!
Big Sur coast:
Active “transform” margin:
Steep topography, narrow
shelf, but no trench or
volcanos..
Passive margin
NO coastal
mountains
WIDE Shelf
(no trench)
Relatively gentle
slope/rise
(few or no canyons)
Passive margin coast
East Coast of US is passive margin
In Both North and
South America:
East Vs. West
coasts are very
different!
VERY Similar
features due to
Active vs. passive
margins
Time for a BREAK
Abyssal Plains
“Plains”
Cont margin generic
Abyssal terrains
Abyssal terrains- Why they are
flat…
Abyssal terrains- what’s
underneath
How do we get this data?
Other ways to map features above
and below the sediments:
“Swath Bathymetry”
Abyssal terrain features
Recall: main shaping forces are Tectonics (sea floor
spreading/ volcanism) + sedimentation
Deep Sea Tenches
What’s the difference between a trench and a canyon?
Trenches are subduction features!
Major Trenches of the world
Trenches
Global RIDGEs
Where would deepest trenches be?
(WHY would some be deeper than others?)
Mariana Trench
Recall: Plate boundary & blue spot
Recall: “THE Blue Spot”
(oldest = most dense crust)
Mariana Trench Flight
http://www.ngdc.noaa.gov/mgg/image/marianas.html
Trieste dive: 1960 made it to bottom (~7 miles
down)…. and back
Bathyscaphe Trieste- late 1950’s
Most of ship = Gasoline “Float” (22,000 gallons)
5” thick steel walls
(plexi-glass window)
9 tons of ballast
Dive of Trieste: Feb 1st 1960
(1940’s technology..)
• Last, Last light ..totally disappeared at ~ 800 ft
•~1hr down- huge “cracking” noise.. they kept
going anyway..
•5 hrs sinking down…
•Hit bottom at 37, 800 ft
•once on bottom saw….
•FISH and crustaceans!
Life Exists in the deepest ocean
No one had
ever been
back…
Until…last
quarter.
NEXT:
Marine sediments!
NEXT:
The Covering of the Sea Floor
Ocean Sediments