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SEPTMEBER 21 2012
LECTURE 7: HISTORY OF MARINE SEDIMENTS
WHAT ARE THEY?
• Eroded rock particles and fragments
• Transported to Ocean
• Deposits that settle through water column
2 types of weathering
Break down of rocks, solid and minerals through direct contact with the planet’s atmosphere.
1.) PHYSICAL WEATHERING: (Heat, water, Ice, pressure) When water becomes ice it expands.
A physical break down of a rock: makes small chunk and more surface area.
More surface area = more area to be weathered.
*Sand breaking down from larger rocks.
2.) CHEMICAL WEATHERING: (Soil,PH,temperature,precipitation,mineral) Acid breakdown w/
sediments and rocks.
Product of respiration = co2
Product of photosynthesis = o2
These two products make carbonic acid. (H2O + CO2 = H2CO3)
Congruent weathering: Results in ONLY dissolved ions.
Limestone weathering = a sedimentary rock consisting mainly of calcium carbonate,
deposited as the calcareous remains of marine animals or chemically precipitated from the
sea: used as a building stone and in the manufacture of cement, lime, etc. = Dissolved ions
Florida sinkholes produced by dissolutions of limestone by carbonic acid. More
weathering – more holes.
Incongruent weathering: Dissolved ions AND clay.
Breakdown sediments w/ grainsized scale go big to small.
Boulders,pebbles,cobbles = gravel
Sands,course and fine = sand
Silt, clay = mud (fine particles)
• Grain size
Proportional energy of transportations and deposition.
(move big = needs a lot of energy /small = little energy)
Why does deep sea have fine grain material and why are beaches sandy?
At the bottom there is slow nonmoving energy.
Sand is slow moving.
Clay and silt > low settling velocity
(takes decades for clay to reach bottom)
Boulders > higher settling velocity
Erosion velocity: Amount of energy it takes to erode sediments. (a lot)
Bottom of Ocean = low energy environment.
1 ES 144 NOTES
SEPTMEBER 21 2012
Takes sand grain one day to sink 4000 m.
Takes clay particles decades.
Silt, 6 months.
Sand erodes easily; clay is much harder to erode.
Classifications of marine sediments: BY ORIGIN
Terrigienous or lithogenous
Hydrogenous (AKA authigenic)
***Most commonly abundant
• Cosmogenous (space)
TERRIGENOUS: (From rivers)
• Most lithogenous sediments are at cont. margins.
• Coarser closer to shore, finer farther from shore
• Mainly mineral quartz
COSMO: space dust, insig. proportion of marine sediments. Macroscopic Meteor debris.
VOLCANO… : ash
* Distributed by wins, streams, submarines, gravity flow, ocean currents and sea ice.
Eroded fragment from land.
Reflect composition of rock from which derived.
Agents of transport.