WEATHERING, EROSION
WEATHERING, EROSION
SEDIMENTOLOGY
SEDIMENTOLOGY
AND THEIR PRODUCTS
AND THEIR PRODUCTS
2 WEATHERING, EROSION
2 WEATHERING, EROSION
& EXAMPLES OF SEDIMENTS AND
& EXAMPLES OF SEDIMENTS AND
PROCESSES OF DESTRUCTION
PROCESSES OF DESTRUCTION
SEDIMENTARY ROCKS
SEDIMENTARY ROCKS
OF OTHER ROCKS
OF OTHER ROCKS
RESULT
RESULT
IN THE MATERIALS ULTIMATELY
IN THE MATERIALS ULTIMATELY
DEPOSITED AS SEDIMENTS
DEPOSITED AS SEDIMENTS
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Rock cycle ver. 2 - summary
Rock cycle ver. 2 - summary
WEATHERING:
WEATHERING:
breakdown of a rock at the earth's
breakdown of a rock at the earth's
surface to form particles/grains
surface to form particles/grains
3 groups of weathering processes:
3 groups of weathering processes:
Physical (esp. in cold & dry climate):
Physical (esp. in cold & dry climate):
mechanical disintegration/disaggregation
mechanical disintegration/disaggregation
Produces
Produces
- clasts (detritus/grains)
- clasts (detritus/grains)
- pebbles, sand, silt, mud)
- pebbles, sand, silt, mud)
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Weathering
Weathering
Chemical (esp. in warm & wet climate):
Chemical (esp. in warm & wet climate):
selective oxidation & dissolution of minerals
selective oxidation & dissolution of minerals
Physical Chemical
Physical Chemical
Produces:
Produces:
- solutions &
- solutions &
- insoluble residue (e.g. laterite, bauxite)
- insoluble residue (e.g. laterite, bauxite)
- clay minerals
- clay minerals
Biological:
Biological:
destruction by chemical & physical processes
destruction by chemical & physical processes
caused by organisms
caused by organisms
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Water: the main agent of weathering
Water: the main agent of weathering
and erosion
and erosion
Water cycle
Water cycle
EROSION:
EROSION:
Removal of the newly formed sediment
Removal of the newly formed sediment
from bedrock
from bedrock
(followed by transportation & deposition)
(followed by transportation & deposition)
4 agents of erosion:
4 agents of erosion:
- gravity
- gravity
- glacial action
- glacial action
- moving water
- moving water
- wind
- wind
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Agents of physical weathering:
Effects of physical weathering:
Temperature variations
Blocky disintegration
Insolation (high daily temp ranges 
Granular disintegration
hot arid climate)
Exfoliation
Freeze-thaw
Expansion of clay minerals (wet climate
= hydration & dehydration)
Stress release: erosion = decrease
of overburden pressure = rock expansion
& fracturing
Biological (mechanical, eg. tree roots)
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Chemical weathering Chemical weathering
Chemical weathering Chemical weathering
Relies on water. CO2 in groundwater releases H ions:
Commonly acidic because of :
" CO2 content) H2O + CO2 = H2CO3 = HCO3- + H2+
" humic acids in soil (organic matter)
Main reactions: oxidation & hydrolysis
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Weathering of granite
Weathering of granite
Chemical weathering (2)
Chemical weathering (2)
Remember the Bowen Reaction Series & apply
Remember the Bowen Reaction Series & apply
to the chermical weathering processes.
to the chermical weathering processes.
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Weathering profile &
Weathering profile &
Bowen Reaction Series & weathering
Bowen Reaction Series & weathering
products (soil formation)
products (soil formation)
processes.
processes.
Saprolite:
weathered
bedrock
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Fossil soils = palaeosols Palaeosols & climatic conditions
Fossil soils = palaeosols Palaeosols & climatic conditions
Temperate climate:
Downward percolation of water
dominates
High organic matter content =
intense weathering of A zone
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Weathering & economic deposits
Weathering & economic deposits
Palaeosols & climatic conditions (2)
Palaeosols & climatic conditions (2)
(BASIC EXAMPLES)
(BASIC EXAMPLES)
Arid climate (dry):
Upward movement of water: capillary rise forced by high
evaporation
Organic matter content very low
Precipitation out of solutions close to surface: "durictrusts"
(latin: durus = hard)
-Calcretes (calcite & dolomite)
-Silcretes (chalcedony)
-Ferricretes (Fe-oxides)
Humid tropical climate:
Laterites  v. rich in Fe & Al
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Weathering & economic deposits (3)
Weathering & economic deposits (3)
Laterite
Kaolin
Bauxite
Uranium roll-front
Other important aspects of chemical weathering:
Eg. karst  importance for hydrogeology  groundwater
resources
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