WHERE DO SEDIMENTS ORIGINATE?
Fig 5.12
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” like
pages 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
►►
Introduced in solution
Al2Si2O5(OH)4 + K+ + HCO3- + SiO2
Clay mineral
Carried away in solution
Products from mechanical /chemical wxg
Dissolved minerals
Solids (residuals)
From chem. wxg
(in solution)
secondary minerals
Primary minerals
from chemical wxg
from mechanical wxg
(clays, iron oxides)
(quartz sand)
CHEMICAL
DETRITAL
Minerals +
organics =
SOIL
(CLASTIC)
SED RX
SED RX
breccia
conglomerate
Conglomerate & breccia
very coarse-grained
detrital rocks formed in
high-energy
environments
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 always
calcite (CaCO3),
grain size is variable
Weathering
Chemical Weathering Processes:
•
Solution of calcite
• CO2 + H20 ► H2CO3
• CaCO3 + H2CO3 ► Ca 2+ + 2 (HCO3)solid
29
solution
solution
solution
Formation of Limestone
Precipitation of Calcite
• CaCO3 + 2 H+ + (CO3)2-
solid
30
solution
Ca 2+ + 2 (HCO3)-
solution
solution
Rock Salt:
a chemical rock
formed from
evaporation of water
(evaporite)
Sedimentary processes
and life processes are intermingled
Fossils are evidence of past life.
They are concentrated in
sedimentary rocks.
• What are fossil fuels?
•Coal
•Oil
•Natural gas
Fossils fuels are concentrated in
sedimentary rocks.
All are organic materials
with C-H bonds
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
►►
Introduced in solution
Al2Si2O5(OH)4 + K+ + HCO3- + SiO2
Clay mineral
Carried away in solution