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 Continental margin Deep-sea Sediment Type Neritic Pelagic Sediment Source Mostly Land (Terrigenous) 1) Biogenous 2) Wind-born 3) Meteorites

Sediment Types (Table 4.1) Type Lithogenous Biogenous Source Eroded Rock Volcanoes Airborne Dust Living Organisms Areas Everywhere Everywhere Hydrogenous Chemical Precipitation Cosmogenous Space Neritic Pelagic Pelagic Examples Sands Muds Red Clay Plants Corals Shells Oozes Mn Nodules Phosphates Micro Meteorites

Particle sizes of marine sediments

General classification Gravel Sand Silt Clay > 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 Lithogenous Biogenous Source Eroded Rock Volcanic ash Airborne Dust Living Organisms Hydrogenous Chemical Precipitation Cosmogenous Space Areas Examples Everywhere Sands Muds Red Clay Everywhere Plants Corals Shells Oozes Neritic Pelagic Mn Nodules Phosphates Pelagic Micro Meteorites

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

 

Sedimentary particles

 

"Weathering" --> fragments Erosion and 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" . . . . . . . . . . . .

. . . . . . . . . . . .

o o o o o o o o o o o o o o o o o o O O O O O O O O O O O O O O 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.