Weathering

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Mass Wasting
Erosion
Soils
Weathering
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Weathering the physical and chemical breakdown
of rock exposed to wind, water, ice, and living
organisms
Regolith loose or broken rock layers resulting
from weathering Regolith covers most of the
earth.
Soil the upper-most layer of regolith that
supports life
3
Do things last for ever ? Consider
new concrete
a 1955 Chevrolet
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Rocks can be broken down or chemically altered on
the earths surface. Mechanical Weathering
Rocks are physically broken down by
various surface processes into smaller parts
without changing physical properties.
Chemical Weathering Rocks are
altered from one form to a
completely new form with a different
set of physical properties.
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I
weathering
Discuss with a friend

• Describe the difference between
• mechanical and chemical weathering.
• 2. Give two examples of MW and CW you
• have observed.

I will get an A on my exams and quizzes
6
Igtclicker question

• Which of the following situation represents
• a form of mechanical type weathering?
• a. a nail that has been rusted
• b. limestone metamorphosed into marble
• c. halite dissolving in water
• d. a crumbling sidewalk

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Mechanical Weathering the breaking down of rocks
How do we expose more surface area for chemical
weathering to do its job ? Lets show some
surface
Rock
More surface area
Less surface area
Increased mechanical weathering accelerates
chemical weathering.
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Types of Mechanical Weathering Processes
Frost Wedging repeated cycles of freezing and
thawing
Water
Water Freezes (expands)
pieces break off (watch for falling rock)
rock
rock
Dominantly takes place in freezing / thawing areas
Unloading reduction of pressure from
overlying rocks -- take the pressure off
me.
overlying rocks
Sheet like structures
granite pluton
Sheet like structures
eroded and uplifted
granite pluton
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Frost Wedging rocks are broken into plates and
split apart.
10
Exfoliation Dome granite is sheeting from
loss of pressure due to unloading processes.
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Types of Mechanical Weathering Processes

• Biological Activity breaking down rocks
  through
• animal burrowing
• humans
• plant roots

Human intervention
Animal burrowing
Plant root weathering
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I
mechanical weathering
Discuss with a friend

• Why is MW important?
• 2. Briefly describe how frost wedging,
• unloading and biological activity
• contributes to mechanical weathering

I will get an A on my exams and quizzes
13
Chemical Weathering Rocks are chemically
altered producing a new compound

• Why would a perfectly good rock want to change
• its appearance?
• STABILITY! Rocks require stability and achieve
• equilibrium with its surroundings
• Most rocks are not chemically stable at the
• earths surface
• Minerals (compositions) change to become stable
• at surface conditions

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• What common agent can begin the process of
  chemical alteration?????
• The Universal Solvent WATER (H2O)

How would we speed up the action of water? Rain
????? What in the atmosphere is added to
water to create a weak acid? H2O (rain)
CO2 (atmosphere) H2CO3 (carbonic Acid)

Lets weather some granite with the natural acid
H2CO3
Granite the most abundant continental rock
weathering the potassium feldspar
(orthoclase)
bicarbonate
potassium
silica
orthoclase
carbonic acid
water
kaolinite clay
2KAlSi2O8 2(H HCO3) H2O
Al2Si2O5(OH)4 2K 2HCO3 4SiO2
Granite has been chemically weathered and broken
down into individual grains.
in solution
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Reduced to Clay
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I
Chemical weathering
Discuss with a friend

• What is the universal solvent?
• 2. How is carbonic acid naturally
• Produced?
• 3. How would you describe the last or
• most reduced material ----- the end
• product of chemical weathering?

I will get an A on my exams and quizzes.
17
Igtclicker question

• The formation of carbonic acid is produced
• by
• a. combining hydrogen and water
• b. combining carbon dioxide and water
• found in the atmosphere
• c. polluted particles in the atmosphere
• d. dissolved gasses absorbed into the
• atmosphere

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Soil product of weathering containing solids,
liquids, and gas.
50 sand 20 silt 30 clay
Whats in your soil?
Loam dominant soil fraction
SILT
CLAY
Humus partially decayed organic
material
CO2/Air fills the soil voids
Water wets the soil and carries high
levels of dissolved substances
SAND
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• Soil Profiles
• horizons a layer of soil with
• distinctive physical and chemical
• properties.
• sequence of soil horizons from
• the surface to the underlying
• bedrock

O
A
E
O- Organic matter (humus)
A- Dark layer mixed with mineral and organic
matter
B
E- light-colored layer produced from removal
of soluble material leaching
C
B- accumulation of clay
C- weathered parent rock
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Factors that influence soil formation

• Parent Material
• residual regolith soil forms emplace or
  insitu

Soil forms and weathers emplace from parent
material.

• transported regolith regolith that is moved by
  rivers,
• wind, and ice

transported river deposits
transported regolith on Mars
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Factors that influence soil formation

• Climate soil profiles differ around the world
• which is directly influenced by
  climate
• arid soils vs. tropical soils

• Living organisms a HUGE influence on soils
• Plants make organic
  matter.
• (humus) animals mix the
  soil
• and recycle air and water.

• Topography the contour or slope of the land

• Time the longer the time the more mature a
• a soil becomes --- 1000s of years

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Classification of soils Soil Taxonomy Soil
classification is based on physical/chemical
properties of a soil
profile, influenced by climate, living
organisms, topography, and time. --- How
many different soils are there? Six categories
of soil classification order
sub-order great groups sub
groups family
series
Broadest
12-basic soil orders Names of soils are derived
from Latin/Greek. Latin solum soil Alfisols
(High-Nutrient Soil) Andisols ((Volcanic
Soil) Aridisols (Desert Soils) Entisols (New
Soils) Gelisols (Permafrost Soils) Histosols
(Organic Soils) Inceptisols (Young
Soils) Mollisols (Prairie Soils) Oxisols
(Tropical Forest Soils) Spodosols (Conifer
Forest Soils) Ultisols (Low-Nutrient
Soil) Verisols (Swelling Clay Soil)
12-orders
Specific
19,000 -series
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Distribution of Earths soils
What soil type (order) characterizes the San
Joaquin Valley?
Alfisols
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I
Sedimentary Rocks
Discuss with a friend

• Draw a typical soil profile and
• identify the common horizons.
• 2. Identify at least 3 factors that
• influence soil formation.
• 3. Describe the difference between
• regolith and soil.

I will get an A on my exams and quizzes.
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• Sedimentary Rocks
• Ig/met rocks represent 90-95 of the Earths
  crust.
• Sediment and sedimentary rock make up 75 of the
  Earths surface
• sediment covers the ocean floor --- except for
  mid-ocean ridges areas
• sedimentary rock concentrated at the surface
  interacting with the
• atmosphere, hydrosphere, lithosphere, and
  biosphere

Sediment/Sedimentary Rock
Igneous/Metamorphic Rocks 90-95 of the crust
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Chapter-6
Sediment
Compaction Cementation
Weathering
Lithification
Transportation
Deposition
Sedimentary Rock Cycle
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Weathering
Transportation
Deposit Sediment

• Sediments are separated into 3-broad categories
• Detrital (clastic) sediments
• inorganic grains or mineral fragments ranging
  in
• size from boulders to clay particles (flour
  size)
• Chemical sediment
• formed by the precipitation of minerals
  dissolved
• in lakes, rivers, or seawater environments
• Biogenic (bioclastic) sediment
• sediment composed of animal and plant remains
  or
• material precipitated by biological processes

To be a sedimentary rock, it must be lithified.
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Lithification processes by which sediment is
transformed into
sedimentary rock
Sediment can be lithified in three common
processes
Compaction Overlying weight of the sediment
squeezes and compresses pore spaces, which
pushes particles together.
A. loose, unconsolidated sediment with
abundant pore space B. compacted, compressed
sediment with reduced pore space
A
B
Cementation Pore water is expelled from voids,
and rising water carries iron, calcium carbonate,
and silica which precipitates as geological glue
(cement) holding the grains.

• Grains are cemented together by three
• types of cements
• iron cement
• calcium carbonate cement
• silica cement

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Lithification processes
Recrystallization Overlying pressure causes less
stable minerals to convert to more stable
minerals, producing new substances that cement
pre-existing grains.
Grain boundaries convert to more stable
mineral compositions, cementing grains together.
Overlying pressure
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Detrital (Clastic) Sediment
Classification based on grain size
lithified
gravel sediment ranging from pea-sized to larger
conglomerate
gt2mm
lithified
sand-sized particles (fine to coarse sandpaper)
sandstone
lithified
1/16 mm
finer particles size of table salt
siltstone
1/256 mm
finest sedimentary particles (flour-size)
lithified
shale
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Chemical Sediments and Sedimentary Rocks
Chemical Sediment sediment formed by the
precipitation of minerals dissolved in a lake,
river, or seawater
All surface water and groundwater contain
dissolved ions, creating a venue for
precipitation of chemical sediment.
Ca2
Ca2
SO2-2
SO2-2
.
Ca2
Ca2
SO2-2
Ca2
Ca2
Ca2
SO2-2

• Precipitation of chemical rocks takes place in
  two ways
• Plants and animals alter the chemical balance
• of the water body (lake, ocean).
• Increasing amounts of calcium carbonate
• cause precipitation of
  limestone.
• evaporation of chemically saturated water
• bodies

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Evaporation of chemically saturated water
creates a chemical sedimentary rock (evaporite).
Na
Na
Cl-
a lake containing sodium (Na) and chlorine
(Cl-)--free ions
Cl-
Cl-
Na
Na
Cl-
Evaporation
Lake water is evaporated, concentrating sodium
and chloride ions (saturation). Sodium and
chlorine combine to form halite (table salt).
NaCl
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The Great Salt Lake, Utah (evaporite halite)
As lake becomes saturated, density of water
increases.
Utah
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Chemical sedimentary rocks that have
been precipitated or are the result of
evaporation
Gypsum evaporite CaSO4
Halite evaporite NaCl
Limestone-- precipitated calcium carbonate
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Varities of Chert-SiO2
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• Biogenic Sediments and Biogenic Rocks
• Biogenic sediment is composed of organic remains
  of plants and
• animals (bioclastic rocks).
• shell, bones, teeth, plant fragments, wood, roots

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• Common Biogenic Rocks
• Limestone
• most abundant biogenic sedimentary rock
• composed of calcium carbonate CaCO3(calcite,
  dolostone,
• aragonite)
• lithified shells, skeletal material

• Chert
• composed of silica SiO2
• precipitated silica shells (made by sea animals)
  that protect
• microscopic sea animals Animals die, and
  silica shells
• sink, creating layers of chert beds on the
  ocean floor.

When the animal dies, it loses the chert off its
back.
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Biogenic (bio-clastic) rocks result from
animal and plant secretions -- The term
clastic indicates that these rocks contain
fossils or parts of plants, shells, compacted
plant material
Animal parts
Cemented shell fragments
Fossil Limestone
Microscopic fossils
Coquina
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Chalk
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• White Cliffs of Dover, England
• made of microscopic hard parts of organisms
• soft, porous material

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Common Biogenic Rocks
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• Peat to Coal
• accumulated remains of terrestrial plants
• with time and pressure ---- peat
• continued pressure and lithification ------ coal

lithification
Peat
Increasing pressure
metamorphism
Anthracite coal
Bituminous coal
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Inorganic (Chemical)
Bio-clastic (Biochemical)
Detrital sedimentary rocks the most common
sedimentary type
Inorganic (Chemical)
Sedimentary Rock Classification Chart
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Sedimentary Rock Classification Summary Tree
Sedimentary Rocks are divided into
3-classification categories
Clastic sediments
Chemical sediments
Bio-clastic (chemical) sediments
formed by precipitation
composed of animal parts
from
composed of inorganic grains
plants and animals
evaporation processes
classification based on distribution of grain
sizes
Classification based on lack of grains and
chemical composition
Conglomerate
Gypsum (CaSO4)
Sandstone
Decreasing grain size
Siltstone
Halite (NaCl)
Shale
Limestone (CaCO3)
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I
Chemical weathering
Discuss with a friend

• Briefly describe the textural differences
• between the 3 categories of sedimentary
• rock classification.

I will get an A on my exams and quizzes.
44
Igtclicker question
Which statement below best describes a chemical
sedimentary rock? a. a rock composed of
inorganic grains visible to the
eye b. a rock composed of fossils c. a rock
produced from the sediment secreted
from plants d. a sedimentary inorganic rock
formed from evaporational processes
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What do sedimentary rocks tell the
earth scientist?
These rock layers were deposited one layer at a
time and lithified. The banded appearance is
known as bedding or groups of layers called
strata. The boundary between each stratum is
called a bedding surface.
Bedding surface
bedding
strata
By observing the sedimentary rock type (clastic,
chemical, biogenic) and depositional patterns, an
earth scientist can decipher the geologic history
like reading pages in a book.
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• Sedimentary Environments
• accumulation of sediments characterized by
  physical and biological
• conditions
• textural and compositional characteristics of
  sediment are clues
• that dictate the type of sedimentary
  environment.
• Continental Sedimentary Environment
• dominated by stream erosion/deposition
• wind erosion producing dune landscapes (eolian
  environment)
• characterized by playa deposits (evaporites)
• glacial deposits unsorted particles (clay to
  boulder size)
• Marine Sedimentary Environment
• Shallow marine (200m to surface)
• boarders the worlds continents (continental
  shelf's)
• sediment type dependent on water depth, climate
• receives large quantities of continental
  sediment
• warm climates carbonate mud's dominant

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Continental
Continental
Transitional
Continental
Continental
Continental
Transitional
Shallow Marine
Deep Marine