Fig 5.12

WHERE DO SEDIMENTS ORIGINATE?

WEATHERING OF PRE-EXISTING ROCKS

HOW ARE SEDIMENTS MOVED? (ERODED/TRANSPORTED)

• water• wind• ice• gravity

WHERE DO SEDIMENTS ACCUMULATE?

75% OF SURFACE ROCKS ARE SEDIMENTARY.

JUST LIKE IGNEOUS ROCKS:

•TEXTURE MEANS SIZE OF GRAINS

Fine-grained Coarse- grained

Sedimentary Rocks:

Form in surface environments (75% of earth’s surface)

Classified according to texture (in part)

Reflect conditions of environment of formation

Accumulate in layers over time (can be “read” likepages in a book)

JUST LIKE IGNEOUS ROCKS:

•TEXTURE IN SEDIMENTARY ROCKS IS A MEANS TO CLASSIFY ROCKS

• BUT ALSO TELLS US ABOUT FORMATION OF ROCK …

• TEXTURE RELATES TO ENERGY OF ENVIRONMENT OF DEPOSITION

WATER SORTS SEDIMENTS ACCORDNG TO SIZE,SO TEXTURE TELLS US ABOUT ENERGY OF E.O.D.

Increasing energy = Increasing particle size

Layered nature of sedimentary rocks reflects depositional processes

What are SOURCES of sediments for sedimentary rocks?

Mechanical Weathering

Chemical Weathering

KAlSi3O8 + H+ + HCO3- + H2O ►►

Potassium feldspar

Al2Si2O5(OH)4 + K+ + HCO3- + SiO2

Clay mineral Carried away in solution

Introduced in solution

Products from mechanical /chemical wxg

Solids (residuals) Dissolved minerals

From chem. wxg

(in solution)

secondary minerals

from chemical wxg

(clays, iron oxides)

Primary minerals

from mechanical wxg

(quartz sand)

Minerals + organics =

SOIL

DETRITAL

(CLASTIC)

SED RX

CHEMICAL

SED RX

Conglomerate & breccia very coarse-grained

detrital rocks formed in high-energy

environments

conglomerate

breccia

Sandstone* a coarse-grained detrital

rocks formed in a medium to high-energy

environment.

* composition of grains is commonly quartz

Shale* a fine-grained detrital rock formed in a

low-energy environment(most common sedimentary rock).

* Composition of grains is almost always clay

Limestone* a chemical rock formed in a

variety of environments,often with the assistance

of organisms(most common chemical

sedimentary rock).

*composition is alwayscalcite (CaCO3),

grain size is variable

• Solution of calcite

• CO2 + H20 ► H2CO3

• CaCO3 + H2CO3 ► Ca 2+ + 2 (HCO3)-

WeatheringChemical Weathering Processes:

solid solution solution solution

29

• CaCO3 + 2 H+ + (CO3)2- Ca 2+ + 2 (HCO3)-

Formation of Limestone Precipitation of Calcite

solid solution solution solution

30

Rock Salt: a chemical rock

formed from evaporation of water

(evaporite)

Sedimentary processesand life processes are intermingled

Fossils are evidence of past life. They are concentrated in

sedimentary rocks.

• What are fossil fuels?•Coal•Oil•Natural gas

All are organic materials with C-H bonds

Fossils fuels are concentrated in sedimentary rocks.

Geologic requirements for oil production:

• source rock

• reservoir rock

• trap

• What is proposed relationship between

fossil fuels and global warming?

Global carbon cycle

Non-metallic mineral resources are concentrated in sedimentary rocks.

• Examples?

• What processes concentrate these materials?

Limestone Quarry

Crushed stone • Price: $6.80 per ton • Volume: 1.1 billion tons• Value? • Relative cost of development?

Copper • Price: $3,230 per ton• Volume: 2.2 million tons• Value?• Relative cost of development?

Chemical Weathering

KAlSi3O8 + H+ + HCO3- + H2O ►►

Potassium feldspar

Al2Si2O5(OH)4 + K+ + HCO3- + SiO2

Clay mineral Carried away in solution

Introduced in solution