Chapter 14: Sediments

Oceanography 2014

Chapter 14: Sediments

1. Stratigraphy

2. Terrigenous Sediments (Lithogenous)

3. Biogenous Sediments

4. Calcareous Ooze

5. Siliceous Ooze

6. Hydrogenous Sediments

7. Evaporites

8. Cosmogenous Sediments

9. Diatomaceous Earth

10.Grain Size

11.Mud

12.Well Sorted Sediment

Vocabulary

Terra- Hydro-Bio- Cosmo-

Root Words

Sedimentation: the accumulation of sediments

Weathering: process of breaking down rocks to create sediments

Erosion: movement of sediments by wind, gravity, or water

Sedimentation

Sediments are classified by grain size and origin Grain Size: from largest (coarse) to smallest (fine) is gravel, sand, silt, and clay

Mud = silt + clayLoam = sand + silt + clay

Origin: land, organisms, chemicals, volcanoes, and space (see table)

Poorly sorted sediment: sample contains a mixture of sediment sizes.Well sorted sediment: sample contains similar or same sized particles.

Sediment Classification

Origin of SedimentsType Origin Composition Location

Terrigenous From land by rivers, glaciers, & wind

Quartz and feldspar(sand and mud)

Rivers: temperate regions All: continental shelves

Biogenous Organisms, Shells, & skeletons

Carbon based; calcium-type (calcareous ooze) and silicon-type (siliceous ooze)

Tropical continental shelves and deep sea

Hydrogenous Chemicals including biochemicals

Ferromanganese nodules; phosphorites (organic debris from upwelling)

Deep sea deposits; continental shelves

Volcanogenic Volcanic eruptions

Cosmogenic Particles that fall from space

Sediment Classifications

Classification Grain Size ExampleClay <0.004 mm Talc, dusty powderSilt 0.004 – 0.0625 mm Heavy powderSand 0.0625 – 2 mm Sugar crystalsGranule 2 – 4 mm Aquarium gravelPebble 4 – 64 mm Grape-sizedCobble 64 – 256 mm Orange-sizedBoulder 256 mm +++ Brick or larger

Where do sediments come from?RiversGlaciersWavesWindsDissolving pieces of living things (biogenous)Chemical reactions

Terrigenous SedimentsMost abundant sediment

45% of all ocean sediment

Found at continental margins, abyssal plains and polar areas

River deposition: Atlantic Ocean: Amazon River Pacific Ocean: very little river deposition

Wind deposition: Dust blown across deserts Sahara Desert – Atlantic Ocean Gobi Desert – Pacific Ocean

What do you see here?

What do you see here?

Biogenic Sediment Second most abundant

Most common throughout the ocean

Found in deep ocean basins

Depends on biological productivity and rate of decomposition

Hard parts of organism preserved Calcareous Siliceous

Calcareous OozeFormed from the

shells of pteropods, forminifera and coccolithophores

Siliceous OozeDiatoms

Biogenic Sediment: Oozes

Low abundance 1% of all ocean sediment

Formed from dissolved solids precipitating out of seawater Most common: manganese nodules

composed of layers of metals such as manganese, iron, nickel, cobalt, and copper

Hydrogenous Sediment

Cosmogenic SedimentLeast abundant SedimentSources include interplanetary dust,

meteorites, asteroids, and comets

Distribution of Sediments

Displays the relationship between particle size and energy for erosion, transportation and deposition.

Hjulstrom’s Diagram

Continental Shelf, Slope and Rise

Controlled by tides, waves and currents

Main type of sediment found: Terrigenous and Biogenous

How is it getting to these areas? River Deposition (large particles) Currents Moving Sediment(sand and large particles) Waves Moving Sediment(silt and clay)

How fast can it accumulate? Depends on area Ranges from 10 centimeters to 7 meters per year

Important note about the Atlantic coast: much of the sediment is trapped by estuaries and does not reach the ocean.

Sedimentation at Continental Margins

Calcareous biogenic sediments dominate tropical shelves. River-supplied sands and muds dominate temperate shelves. Glacial till and ice-rafted sediments dominate polar shelves.

Shelf Sediment Type by Region

Sedimentation at Deep Ocean BasinsMain type of sediment found: Terrigenous,

Biogenous, and Hydrogenous

Sediments Found: Manganese Nodules (hydrogenous) Turbidites (terrigenous) Clays (terrigenous)

Cover 31% of deep ocean Accumulation: 2 mm/ 1000 years

Oozes (biogenic) Accumulation: 1-6cm/ 1000 year

Tools and Techniques:1. Clam-Shell “Grab” Samplers2. Piston Corers3. Deep-Sea Drilling4. Seismic Profiling

Studying Sediments

Grab samplers take a “bite” out of the sediment covering the bottom.

Corers use a weight to drive a core barrel into a soft bottom.

Economics1/3 of oil and gas reserves are on the continental

marginsSand and Gravel from ocean sources are a $480

million industry

MedicinesMicrobes living in ocean sediment have been used to

make antibioticsIn 2003, a group of bacteria was found within ocean

sediment that could be used to make a medicine to treat cancer

Why are Sediments Important?

Oceanography March 19, 2014

What are sediments? Where do they come from?

Oceanography March 21, 2014Sediment Classification

1. Name two ways sediments can be classified.

2. What does “bio” mean? How does that relate to a type of marine sediment?

Oceanography March 20, 2014Sediment Types

1. What role does weathering and erosion play on the introduction of sediments to the ocean?

2. Speculate on why you think cosmogenic sediments would be the least common.

Oceanography March 28, 2014Sediment Sampling

1. Why would scientists want to collect samples of oceanic sediment?

2. What are two types of information that could be determined from a sample of ocean sediment.

3. Name two ways sediment can be sampled.

Oceanography March 20, 2014Biogenic Sediments

1. What are the two types of biogenic sediment?

2. How do they form?3. Hjulstrom’s Diagram

Oceanography March 20, 2014Sedimentation Factors

What does a Hjulstrom’s Diagram explain?

Oceanography March 20, 2014Continental Sedimentation

What factors control sedimentation at continental margins?