Marine Province Flashcards
Passive continental margins
Lacks a plate boundary
Low degree of plate tectonic activity
3 major ocean floor provinces
Continental margins
Deep ocean basins
Mid ocean ridge
Active continental margin
High degree of tectonic activity
Includes convergent active margins and transform active margins
Continental shelf
Generally flat zone extending form the shore beneath the ocean surface to the shelf break
Shelf break
A point at which a marked increase in slope angle occurs
Continental shelf average width and range in km
70 km but varies to 1500 km
Shelf break average depth in meters
135m
Continental slope
Lies beyond shelf break and is where’s the deep ocean basins begin
Which North American continental margin has a continental slope with a steeper average gradient
Pacific margin
Submarine canyons
Narrow nut deep submarine valleys that are V shaped in profile view and have branches or tributaries with steep over hanging walls
Constrast the size of the Monterey Submarine Canyon and the Grand Canyon
Comparable in size in terms of length width and steepness
Average depth of continental slope
3500m below sea level
Why the portions of submarine canyons below a few hundred meters could not have formed by stream erosion
Many are not directly offshore where rives enter the the sea and many are confined to the continental slope
Contrast the shapes of submarine canyons confined to the continental slope to canyons that cut across the continental shelf
Canyons confined to the continental slope have straighter and steeper canyon floor gradients
Explain the formation of most submarine canyons
Turbidity currents
Turbidity currents
Underwater avalanches of muddy water mixed with sediments that move down the continental slope
Triggering mechanisms for turbidity currents
Shaking by earthquake
Overstepping of sediment that accumulates on the shelf
Hurricanes passing over the sea
Rapid input of sediment from flood waters
Continental rise
Transition zone between the continentals margin and the deep ocean floor comprised of huge submerges piles of debris
Formation of continental rise
When a turbidity current moves through and erodes a submarine canyon, it exits through the mouth of the canyon. The angle of the slope decreases and the turbidity current slows down causing the material to settle
How grade bedding sequences in continual rises form
As the energy of the turbidity current dissipates in a submarine canyon, the larger pieces settle first, then progressively smaller pieces settle, and eventually the very fine pieces settle out.
Deep sea fan
The deposits at the mouths of submarine canyons that are fan shaped
Role of deep sea fans in the formation of continual rise
They create the continental rise when they merge together along the base of the continual slope
Why continental rise often do not form along active continental margins
The steep continental slope leads directly into a deep ocean trench. Sediments from turbidity currents accumulates km the trench causing failure in continental rise
Indus deep sea fan’s length
1800 km
