1

SEDIMENTOLOGY

SEDIMENTOLOGY

2

2

WEATHERING

WEATHERING

,

,

EROSION

EROSION

& EXAMPLES OF SEDIMENTS AND

& EXAMPLES OF SEDIMENTS AND

SEDIMENTARY ROCKS

SEDIMENTARY ROCKS

2

WEATHERING

WEATHERING

,

,

EROSION

EROSION

AND THEIR PRODUCTS

AND THEIR PRODUCTS

PROCESSES OF DESTRUCTION

PROCESSES OF DESTRUCTION

OF OTHER ROCKS

OF OTHER ROCKS

RESULT

RESULT

IN THE MATERIALS ULTIMATELY

IN THE MATERIALS ULTIMATELY

DEPOSITED AS SEDIMENTS

DEPOSITED AS SEDIMENTS

Rock

Rock

cycle

cycle

ver

ver

. 2

. 2

-

-

summary

summary

4

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

Physical

(esp. in cold & dry climate):

(esp. in cold & dry climate):

mechanical disintegration/

mechanical disintegration/

disaggregation

disaggregation

Produces

Produces

-

-

clasts

clasts

(detritus/grains)

(detritus/grains)

-

-

pebbles, sand, silt, mud)

pebbles, sand, silt, mud)

5

Chemical (

Chemical (

esp. in warm & wet climate):

esp. in warm & wet climate):

selective oxidation & dissolution of minerals

selective oxidation & dissolution of minerals

Produces:

Produces:

-

-

solutions &

solutions &

-

-

insoluble residue (e.g.

insoluble residue (e.g.

laterite

laterite

, bauxite)

, bauxite)

-

-

clay minerals

clay minerals

Biological:

Biological:

destruction by chemical & physical processes

destruction by chemical & physical processes

caused by organisms

caused by organisms

6

Physical

Physical

Weathering

Weathering

Chemical

Chemical

2

7

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

8

Water: the main agent of weathering

Water: the main agent of weathering

and erosion

and erosion

Water cycle

Water cycle

9

Agents of physical weathering:

Temperature variations

Insolation (high daily temp ranges –

hot arid climate)

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)

10

Effects of physical weathering:

Blocky disintegration
Granular disintegration
Exfoliation

11

Relies on water.
Commonly acidic because of :

• CO2 content)
• humic acids in soil (organic matter)

Main reactions: oxidation & hydrolysis

Chemical weathering

Chemical weathering

12

Chemical weathering

Chemical weathering

CO

2

in groundwater releases H ions:

H

2

O + CO

2

= H

2

CO

3

= HCO

3

-

+ H

2

+

3

13

Chemical weathering (2)

Chemical weathering (2)

14

Weathering of granite

Weathering of granite

Remember the Bowen Reaction Series

Remember the Bowen Reaction Series

&

&

apply

apply

to

to

the

the

chermical

chermical

weathering processes

weathering processes

.

.

15

Bowen Reaction Series

Bowen Reaction Series

&

&

weathering

weathering

processes

processes

.

.

16

Weathering profile &

Weathering profile &

products

products

(soil formation)

(soil formation)

Saprolite:
weathered
bedrock

17

Fossil soils =

Fossil soils =

palaeosols

palaeosols

18

Temperate climate:
Downward percolation of water
dominates
High organic matter content =
intense weathering of A zone

Palaeosols

Palaeosols

& climatic conditions

& climatic conditions

4

19

Palaeosols

Palaeosols

& climatic conditions (2)

& climatic conditions (2)

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

20

Weathering

Weathering

& economic deposits

& economic deposits

(BASIC EXAMPLES)

(BASIC EXAMPLES)

21

Weathering

Weathering

& economic deposits (3)

& economic deposits (3)

Laterite
Kaolin
Bauxite
Uranium roll-front

Other important aspects of chemical weathering:
Eg. karst – importance for hydrogeology – groundwater
resources