Continental Margin, Slope
and Ocean Basin
depositional systems
Presented by: Haritha Dilshan
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Introduction
Marine waters cover nearly 71% of the Earth’s surface. And, if we subtract the 6% area of the
continental shelf, 65 % of the earth's surface is occupied by continental slope and rise, and deepsea parts.
The deep parts of the ocean receive sediment from the continents through a set of connected
environments. These environments begin at the edge of the continent, pass down a steep
transitional zone, and reach the deep floor of the ocean. Each zone has its own geometry,
processes and characteristic deposits.
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Continental Margin
• The continental margin is the submerged edge of the continent. It includes the continental
shelf, the continental slope and the continental rise. These areas together form the transition
from the land to the deep ocean.
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Parts of the Continental Margin
Continental
Shelf
A shallow submarine platform at
the edge of a continent, inclines
very gently seaward,.
The sediment is usually sand
near shore, where the bottom is
shallow and influenced by wave
action.
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Underwater topography of the Mid-Atlantic Ocean
Continental Shelf
Deposits and Structures
•
Waves, tides and storms are dominated
here.
•
After sediment settles and lithifies in the
continental margin, the rocks usually show
wave ripples, tidal bundles and storm beds
marked by hummocky cross stratification.
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Parts of the Continental Margin
Continental Slope
• It is a steep slope that extends
from a depth of 100 to 200 meters
at the edge of the continental shelf
down to oceanic depths. The
average angle of slope for a
continental slope is 4∘ to 5∘ . But in
some areas, it may be 20∘
• Continental slopes are temporary
depositional sites of sediments.
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Continental Slope
Deposits and Structures
•
Deposition is by gravity flow processes
ranging from submarine slides and slumps
to debris flows and turbidity currents.
•
Submarine canyons carve steep, narrow
pathways down the slope and guide
turbidity currents toward the basin floor.
•
These currents carry dense mixtures of
sand, silt, clay and water.
•
When they slow at the continental rise, the
sediment settles into turbidites that show
clear graded bedding.
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Parts of the Continental Margin
Continental Rise
• Along the base of the continental
slope lies the continental rise, a
wedge of sediment that extends
from
the
lower
part
of
the
continental slope to the deep-sea
floor.
• The continental rise, which slopes
at about 0.5°-1°, more gently than
the continental slope.
• The environment in the continental
rise is quite and unique.
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Continental Rise Deposits and Structures
•
It is the landing zone where gravity flows (C)
C
coming down the slope lose their speed and drop
their load.
•
D
The rise is usually built from submarine fans (B).
These fans have channels and levees near their
B
A
upper parts and sheet like lobes farther out.
•
Lower parts of a bed show coarse sand with
parallel lamination and cross lamination, while the
upper parts grade into rippled lamination and mud
(A) match the Bouma sequence.
A – Graded bedding
B – Submarine Fans
C – Turbidity flow
D – Submarine canyons
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Ocean Basin
• The ocean basin is the deep floor of the ocean
that lies far beyond the continental rise. It is a
quiet, low energy environment where very fine
sediment settles through the water to the
seafloor.
• Sediment in this region shows well-developed
graded bedding, coarse grained near the
bottom and finer-grained toward the top and
ultimately merging to pelagic sediment layers.
• Its surface includes broad abyssal plains,
abyssal hills, seamounts, guyots and deep
trenches.
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Ocean Basin
Features
• Abyssal plains
Very broad, flat areas covered by fine muds and distal
turbidites.
• Abyssal hills
Low, gentle topographic highs formed by faulting or volcanic
activity on the seafloor.
• Seamounts and guyots
Underwater volcanic mountains. Guyots have flat tops
trimmed by wave erosion before subsidence.
• Deep-sea trenches
Very narrow, deep depressions formed at subduction zones.
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Thank you!
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