OCEANOGRAPHY ch 5
Calcareous Ooze:
- organisms live in all surface waters of the ocean. BLANK is present on the deep‐sea floor up to 4500 meters deep Ooze does not accumulate all over the sea floor. - WHY??
Hydrogenous Sediments: NODULES
-Mostly manganese and iron oxides; recent evidence of phosphorites Also Co, Ni, Cr, Cu, Mo, Zn -Very slow accumulation: 1‐10 mm per million years -form around shark teeth and animal skeletons
tools used to study marine sediments
-deep sea cameras -clamshell sampler: for shallow sediment samples -deep sea drilling -piston corer -seismic profiling
Where do terrigenous sediments come from?
-from continents and rivers -blown dust -volcanic eruptions
As salinity increases, precipitation occurs:
1. Calcium carbonate (forms limestone) 2. Calcium sulfate (forms gypsum) 3. Sodium chloride (table salt)
Why are marine organisms made of siliceous and calcareous materials?
1. Compounds with silicon and calcium carbonate entered the oceans from river input and from dissolution at oceanic ridges. 2. Plants and animals used the compounds from the seawater to make skeletons. 3. Most of the organisms using these materials are plankton (drifting species) 4. When plankton and other animals die, their skeletons sink to the bottom of the ocean.
Cycle of CaCO3 Dissolution at Depth:
1. Deep seawater has more CO2, which increases acidity. 2. Greater acidity, cold water, and high pressure at depth increases solubility of CaCO3. Shells dissolve rapidly.
How do hydrogenous sediments come out of the seawater?
1. Dissolved from underwater rocks and sediments 2. Leaching from new crust at seafloor spreading centers 3. Hydrothermal vents 4. River runoff
Recipe for Oolite Sand:
1. Shallow water with high biological productivity 2. Sunlight to heat water 3. Plankton use carbon dioxide 4. Seawater becomes less acidic 5. Calcium carbonate precipitates out of seawater to maintain equilibrium
Erosion and deposition
1. When oceanic crust collides with continental crust, mountains rise up. 2. Wind and water erode sediment from mountain tops. 3. Sediment is carried to the sea by wind, streams, and rivers. 4. Sediments are deposited on the seafloor. 5. Sediment move with plates and get uplifted or subducted. 6. Either way, sediments are recycled.
Fine grains:
1. moved by suspended flow 2. settle at a slower rate
Coarse grains:
1. moved by turbulent flow 2. settle at a faster rate
dust & ashes
100 million metric tons/year of sediment from land to ocean
rivers
15 billion metric tons/year of sediment from land to ocean
Accumulation of ooze depends on three things:
1‐abundance of organisms at the surface 2‐dissolution rate as they sink to the bottom, 3‐accumulation of terrigenous sediment
hydrogenous sediments
Also called authigenic sediments: formed in the same place that they now occupy
sorting
BLANK is a function of energy in the environment
Terrigenous (Lithogenous) Sediments:
Before they come from the land, they come from igneous rock.
largest area
Biogenous sediment makes up the BLANK of ocean sediment.
manganese nodules
Commercial mining of BLANK has also been considered.
fecal pellets
Conundrum: If fine particles of benthic sediments take so long to settle (i.e. 20‐50 years), then why does the benthic sediment composition reflect the particle composition of the overlying pelagic water column?
seismic profiling
Determines thickness and structure of sediment layers on the continental shelf and slope. Finds oil and gas fields. Ship tows a sound transmitter and receiver behind it.
Grand canyon
Example of lithified sedimentary continental shelf deposits
sand and gravel
In 2005,BLANK & BLANK valued at more than $550 million were taken from the ocean.
sedimentary deposits
In 2010, an estimated 39% of the world's crude oil and 35% of its natural gas was extracted from the BLANK of continental shelves and continental rises.
How do oolite sands form?
Less acidic seawater or warmer seawater can initiate precipitation
Where do sediments come from?
NODULES PHOSPHATES CARBONATES METAL SULFIDES EVAPORITES
hydrocarbons
Offshore BLANK currently generate annual revenues in excess of $200 billion.
How old are ocean sediments?
Rarely older than 180 million years
Oolite Sands:
Rounded grains of precipitated calcium carbonate on shell fragments and small particles
Evaporites:
Salts precipitate as water evaporates from small sections of oceans, landlocked seas, or landlocked lakes.
ooze
Sediment containing at least 30% biogenous material From Marine Organisms Made up of single‐celled planktonic organisms and the single‐ celled animals that feed on them.
Why are very few areas of the seabed completely free of sediments?
Sediment is in the overlying water column but it may not collect -strong currents -seafloor young
pelagic sediments
Sediments of the slope, rise, and deep‐ocean floors are BLANK, and contain a greater proportion of biogenous material.
oozes
Skeletons settle and mix with terrigenous sediment - forms BLANK (both siliceous and calcareous) Slow accumulation rate: 1‐6 cm per thousand years
highest volume
Terrigenous (Lithogenous) sediment makes up the BLANK of ocean sediment.
Sediment
The accumulation of inorganic and organic particles in a loose, unconsolidated form ex) beach sand, bay, mud, shell deposits, benthic clay, abyssal oozes, deep sea nodules
neritic sediment
The sediment of continental shelves is called BLANK and contains mostly terrigenous material.
sediments are historical records
The youngest sediments are closest to the seafloor spreading center. The oldest sediments are closest to the subduction zone.
lification
White Cliffs of Dover, England Formed by BLANK: sediments converted to sedimentary rock by pressure‐induced compaction or cementation; lifted up by tectonic activity
Calcium Carbonate Compensation Depth (CCD)
below this depth, no calcareous ooze accumulates because the rate of dissolution is higher
color of sediments
depends on the origin -biological origin -red oxidized clay
siliceous ooze
found at great depths OR in cold, polar regions
fecal pellets
from animals; much larger than individual skeletons of diatoms, foraminfera, and other plankton Fall to the ocean floor in about two weeks!
Most marine sediments are made of
sand, silt, and clay particles.
Microtektites
‐ Particles of glass that formed from violent impact of meteors or asteroids hitting the Earth's surface
Interplanetary Dust
‐ Silt‐ and sand‐sized particles that enter the atmosphere from asteroids and comets ‐Large particles create friction with the atmosphere and light up ‐ most of material dissolves before reaching the sea floor
Calcareous Organisms
‐ contain calcium carbonate (CaCO3) ‐ coccolithophores (type of algae) ‐ foraminifera (type of protozoa)
mostly terrigenous sediments
‐ eroded from land ‐ carried by streams and rivers to the ocean ‐ currents distribute large particles (i.e. sand) along the coast ‐ waves carry small particles (i.e. silt and clay) to deeper water
radiolarians
‐ protozoa ‐ most common in equatorial regions ‐ west coast of South America
Poorly Sorted Sediments (high energy fluctuations)
‐Composed of particles of a mixture of sizes ‐Formed in places of high energy fluctuations ‐Example: base of an eroding shore cliff
Well‐Sorted Sediments (low energy fluctuations)
‐Composed of particles of mostly one size ‐Formed in places of low energy fluctuations ‐Example: deep‐ocean floor sediments
Benthic Sediments:
‐Deep water deposits ‐ fine‐grained particles ‐ higher proportion of biogenous sediments ‐ deposited slowly
sediment core tells us
‐Sediment movement and plate tectonics ‐ evolution of life‐forms through fossils ‐ climate change history
Neritic Sediments:
‐Shallow water ‐ close to land ‐ mostly terrigenous ‐ deposited quickly
Siliceous Organisms
‐contain silicon dioxide (SiO2) ‐ diatoms (type of algae) ‐ radiolarians (type of protozoa)
Granite (continental crust):
‐cools slowly ‐Crystals form during slow cooling ‐ granite is the source of quartz and clay ‐ almost all terrigenous sediment comes from granite rock
Turbidity Currents
‐current is powered by gravity ‐ mixture of suspended particles is denser than seawater ‐ transports coarse particles from the coast to the deep‐ ocean floor
Pennate Diatoms
‐single‐celled algae ‐ most common in deep, polar waters ‐ ocean basins around Antarctica
Ocean Sediments Vary Greatly in Appearance
• Particles of organic or inorganic matter that accumulate in a loose, unconsolidated form that vary according to: - Size - Source - Location - Color
Classification of Marine Sediments
• Size or Texture • Composition • Origin • Deposition Site
