Transcript No Slide Title

No Quiz This Week
• Exam tomorrow night; here, 7 PM
• Bring a pen/pencil you can write a short
essay with
• Extra credit (up to 5% extra)- redo the
exam with discussion in small groups
(8:00)
So Far, We’ve Covered...
• Basic Earth Properties and Maps
• Ocean Basin Features
• Plate Tectonics
What’s Next?
• Sediments
• Ocean Water: Physical Properties
– Density, Evaporation
• Ocean Water: Chemical Properties
– Dissolved matter
– Salinity
– Nutrients
Class #11
OCEAN SEDIMENTS
Introduction
Marine sedimentary provinces
Importance of particle size
Terrigenous sediments
Turbidity currents
"The sediments are a sort
of epic poem of the Earth."
-Rachel Carson
Ocean sediments are our best record
of Earth history!
Ocean sediments are somewhat like a book
of earth history- every detail says something
about events on the earth.
Many sedimentary rocks can be found on
land today.
Sedimentation Patterns
•Layering -- oldest at bottom, youngest at top
•How thick are they?
–very little on mid-ocean ridges
–up to 10,000 m beneath continental rises
–average = 500 m
•Sediments collect slowly
–Deep ocean (avg.): 0.5 - 1.0 cm/1000 yr
–Continental margins: 10 - 50 cm/1000 yr
–River mouths may be higher
•Where does all this stuff come from?
•Continents (weathering and erosion)
•Biogenic particles
•Volcanic ash
•Chemical precipitates
•Micro-meteorites
•Why do we care?
•Oil, gas, and other resources
•Record of past conditions and
processes
Neritic
Marine Sediment Provinces
Area
Sediment
Type
Sediment Source
Continental
margin
Neritic
Mostly Land
(Terrigenous)
Deep-sea
Pelagic
1) Biogenous
2) Wind-born
3) Meteorites
Sediment Types (Table 4.1)
Type
Source
Lithogenous
Eroded Rock
Volcanoes
Everywhere
Airborne Dust
Living
Everywhere
Organisms
Biogenous
Hydrogenous
Chemical
Precipitation
Cosmogenous Space
Areas
Neritic
Pelagic
Pelagic
Examples
Sands
Muds
Red Clay
Plants
Corals
Shells
Oozes
Mn Nodules
Phosphates
MicroMeteorites
Particle sizes of marine sediments
General classification
Gravel
Sand
Silt
Clay
Particle diameter, mm
>2
0.06 - 2
0.004 - 0.06
< 0.004
"Mud" -- silt and clay
Coarse
Finer
Finest
Particles Sizes in Sediment- Interpretation
(1) Larger --> sink faster
(2) Faster-moving water holds coarser sediment
and more of it.
(3) Rapid currents transport coarse + fine seds.
(4) Slow currents transport only fine sediments.
So….
•Coarsest Particles: beaches, near-shore, inner
shelf -- "fast" currents
•Finest: quieter places
Sediment Types (Table 4-1)
Type
Source
Areas
Lithogenous
Eroded Rock
Volcanic ash
Airborne Dust
Living
Organisms
Sands
Everywhere Muds
Red Clay
Everywhere Plants
Corals
Shells
Oozes
Neritic
Mn Nodules
Pelagic
Phosphates
Pelagic
MicroMeteorites
Biogenous
Hydrogenous
Chemical
Precipitation
Cosmogenous Space
Examples
LITHOGENOUS SEDIMENTS
(1) Terrigenous sediment
– ~75% of all marine sediment (by mass)
– Mostly settles on continental margins
•So they DO NOT cover a very large area
– Atlantic: Large “fans” spread out on the
deep-sea floor
– Pacific Ocean: Trapped by trenches; little
transported to deep-sea floor
Erosion removes material from land:
Where does it go?
Continental
rocks
"Weathering" -->
fragments


Sedimentary
Erosion and
particles
transport

-- streams, rivers

-- wind
-- glaciers
Continental
margins
Turbidity Currents:
Move sediment down the continental margins
Turbidity Currents
•Dense, muddy water
(turbid water) cloud or
slurry that flows down
the continental slope
onto the continental
rise- HUGE
•Turbidity current: dense slurry (“avalanche”) of
poorly sorted, suspended sediment
•Sediment deposited as current slows
•Largest particles settle first (poorly
sorted)
•Finer particles settle next
•Finest particles (mud) settle last
Turbidity Currents
http://faculty.gg.uwyo.edu/heller/sed_video_downloads.htm
Result -- a "graded bed"
............
............
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OOOOOOO
Finest sediment
particles
Coarsest
sediment particles
LITHOGENOUS SEDIMENT- Pelagic
(2) "Red Clay" -- terrigenous dust + volcanic ash
–Transported to open ocean by winds + water
currents
–Settles eventually
–Dominant only in deep areas where other
types absent.