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Earth Science
Chapter 13 - The Ocean Floor
39
Science
5th Grade
02/19/2006

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Term
Three major ocean basins
Definition
Pacific
Atlantic
Indian
Term
What is the dominant feature of the ocean floor?
Definition
the mid-ocean ridge system


other major: deep ocean trenches
Term
Continental Margin
Definition
the boundary between the continents and the deep ocean basins
Term
Three components of
the continental margin
Definition
continental shelves

continental slope

continental rise
Term
Continental shelves
Definition
submerged upper part of continental margin

shoreline to shelf break
Term
Continental Slope
Definition
steeper part of continental margin

outer edge coincides with geologic edge of the continents
Term
Continental Rise
Definition
starts at the base of the continental slope, and eventually connects with the deep sea floor

large apron of sediment

rises are broad and less rugged
Term
Coastal Plains
Definition
former areas of the continental shelf that are now exposed above sea level
Term
Submarine canyons
Definition
cut through the continental shelves and slopes

similar to rift valleys in morphology

associated with large river systems

probably formed as river valleys when seal level was much lower
Term
Mid-Ocean Ridges
Definition
continuous elevated zone on all major ocean basins

has steep-sided central rift valley, site of:
basaltic volcanism
shallow focus earthquakes
hydrothermal vents

ridges are relatively narrow and rugged
Term
abyssal hills
Definition
areas of low rolling topography

many appear to e extinct volcanoes covered by sediment
cover 80% of pacific basin and much of indian ocean
Term
abyssal plains
Definition
extensive, flat areas of the sea floor

occur at the base of the continental rises

areas of thick deposits of sediment that has buried original topography
Term
fracture zones
Definition
narrow elongated zones of rugged topography with steep ridges and valleys

extensions of transform faults from the mid-ocean ridges

parallel eachother
Term
trenches
Definition
deepest parts of the ocean floor

relatively narrow, but long

usually associated with volcanic arcs
Term
Ocean Plateaus
Definition
isolated portions of the ocean floor that stand a kilometer or more above their surroundings

found in all ocean basins

can be microcontinents or associated with volcanic activity
Term
Pacific Basin
Definition
more than half the world's water

deepest

bounded by active continental margins,
including trenches and volcanoes

islands abundant
numerous marginal seas
few rivers empty into pacific
Term
Atlantic Basin
Definition
relatively narrow,
bounded by parallel continental margins

greatest extent is in N-S direction

many rivers drain into Atlantic

highest salinity
due to high sediment transport and surface runoff

few islands
several marginal seas

Arctic Ocean is an extension of the Atlantic Basin
Term
Indian Basin
Definition
shortest in N-S extent

esentially straddles equator

intermediate depth

few islands or marginal seas

proximaty of continents leads to rapidly changing climatic conditions from summer to winter (monsoons)

3 of largest rivers empty, supplying significant sediment
Term
Marginal Ocean Basins
Definition
large ocean-bottom depressions near continents

separated from open ocean by submarine ridges or islands
Term
3 Types of Marginal Ocean Basins
Definition
those associated with volcanic island arcs

basins that lie betwen continents

long, narrow basins surrounded by continent
Term
Passive Margins
Definition
found along coastal areas surrounding atlantic ocean

experience very little volcanic activity and few earthquakes

includes continental shelf, slope, and rise
Term
active margin
Definition
occur where oceanic lithosphere is being subducted beneath the edge of a continent

narrow margin

sediments from ocean floor are scraped from the descending plate and added to the continental crust as an accretionary wedge

common around Pacific Rim, parallel deep ocean trenches
Term
bathymetry
Definition
the measurement of ocean depths and the carting of the topography of the ocean floor
Term
hypsographic curve
Definition
method used by oceanographers to visualize land and ocean relationships; terrain relief
Term
lithogenous/terrigenous sediment
Definition
material derived from the continents or associated with oceanic volcanism (clay, silt)

transported to oceans by rivers, glaciers, and wind

sedimentation rates variable

found close to source
Term
biogenous sediment
Definition
derived from biological activity; remains of plants and animals
(shells, bone, teeth)

distribution controlled by:
biological productivity in surface waters
dilution by other sedimenet types
chemical dissolution
destruction by scavengers or burrowing organisms
Term
hydrogenous sediment
Definition
formed from seawater through chemical reactions (nodules and crusts)

both marine and freshwater

form in areas of low sedimentation rates or areas of net erosion

produce particles, concretions, crusts, or coatings
Term
cosmogenous sediment
Definition
fine dust and small particles that fall into the ocean from space (tektite)
Term
Ocean sediments are usually classified according to ___
Definition
source
Term
relict sediment
Definition
sediment deposited under conditions that no longer exist

for example, fluvial sediments deposited on the current continental shelves during the last glacial age when sea level was lower
Term
ooze
Definition
sediment contains more than 30% of skeletal (shells or bone) debris

two types:
silicerous: silica shells
calcareous: CaCO3 shells
Term
red clay
Definition

lithogenous sediment

color due to coating of oxidized iron
Term
kinds of lithogenous sediment
Definition
deep-sea muds or red clay

terrigenous sediment: land

glacial marine

relict sediment
Term
what processes control the distribution of
biogenous sediments?
Definition
biological productivity in surface waters
dilution by other sediment types
chemical dissolution
destruction by scavengers or burrowing organisms
Term
why study ocean sediments?
Definition
ocean is a site of deposition

generally undisturbed

deposited under slowly changing conditions
retain organized record of earth history
explain past climates
explain evolution of life
economically important resources
oil, natural gas, minerals
Term
what affects the global distribution of marine sediments?
Definition
proximity to source areas

water temperatures
that favor the growth of certain marine organisms
Term
suspended sediments
Definition
material transported to the oceans by rivers or wind

transport affected by particle size. particle shape, ocean currents

the smaller the particle, the slower the settling rate
Term
rates of settling of sand, silt, clay
Definition
sand - fastest 4 km/1.8 days
silt - 4 km/185 days
clay - 4 km/50 years
Term
methods of transport
Definition
wind
turbidity currents along bottom
rivers - continental margins only
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