1

Sedim

entary Rocks and

Sedim

entary Rocks and

Processes

Processes

Sedim

entary Processes

Sedim

entary Processes

��Weathering

Weathering

��Breakdown of pre

Breakdown of pre-- existing rock by physical and

existing rock by physical and

chemical processes

chemical processes

��Transport

Transport

��Movement of sedim

ents from environments of

Movement of sedim

ents from environments of

relatively high potential energy

relatively high potential energy

��Deposition

Deposition

��Settling of sedim

ents in environments of relatively low

Settling of sedim

ents in environments of relatively low

potential energy

potential energy

��Diagenesis

Diagenesis

��Chemical changes that occur after sedim

ents are

Chemical changes that occur after sedim

ents are

buried

buried

Sedim

entary Processes

Sedim

entary Processes

��Weathering

Weathering

��Physical Weathering

Physical Weathering

��Mechanical breaking of rock into smaller pieces (clasts)

Mechanical breaking of rock into smaller pieces (clasts)

��No new m

inerals form

ed

No new m

inerals form

ed

��Chemical Weathering

Chemical Weathering

��Reaction of rocks with air or water

Reaction of rocks with air or water

��New m

inerals form

ed at the expense of less stable m

inerals

New m

inerals form

ed at the expense of less stable m

inerals

��Transport

Transport

��Deposition

Deposition

��Diagenesis

Diagenesis

Physical Weathering

Physical Weathering

��Abrasion

Abrasion

��Grinding of rock fragments (e.g., sandblasting)

Grinding of rock fragments (e.g., sandblasting)

��Frost Wedging

Frost Wedging

��Ice is approxim

ately 8% greater volume than an equal number of m

Ice is approxim

ately 8% greater volume than an equal number of moles of

oles of

water

water

��Ice in cracks expands and creates an extensional stress

Ice in cracks expands and creates an extensional stress

��Salt Crystallization

Salt Crystallization

��Salt crystals that precipitate in cracks due to evaporation of s

Salt crystals that precipitate in cracks due to evaporation of saline

aline

solutions will expand when heated and create stress

solutions will expand when heated and create stress

��Exfoliation

Exfoliation

��Rock breaks apart in layers that are parallel to the earth's sur

Rock breaks apart in layers that are parallel to the earth's sur face

face

due to expansion when overlying m

aterial is eroded

due to expansion when overlying m

aterial is eroded

2

Abrasion of Brownstone

Abrasion of Brownstone

Frost Wedging of Brownstone

Frost Wedging of Brownstone

Chemical Weathering

Chemical Weathering

��Dissolution

Dissolution

��HH

22CO

CO

33+

+ C

aCO

CaCO

33→→

Ca

Ca2+

2+(aq)

(aq) + 2HCO

+ 2HCO

33--(( aq

aq))

��Dissolution of calcite in carbonic acid

Dissolution of calcite in carbonic acid

��All rainwater is a weak carbonic acid solution

All rainwater is a weak carbonic acid solution

��CO

CO

2 (g)

2 (g)+ H

+ H

22O

O (l)(l)↔↔

HH22CO

CO

3(aq)

3(aq)↔↔

HH+

+ (( a

qaq))+ HCO

+ HCO

33--(aq)

(aq)

��NaCl

NaCl→→

Na

Na++

(( aq

aq))+ Cl

+ Cl--

(( aq

aq))

��Dissolution of halite in water

Dissolution of halite in water

��Would you expect to find halite in outcrop?

Would you expect to find halite in outcrop?

��Would calcite be more resistant in wet or dry climates?

Would calcite be more resistant in wet or dry climates?

Dissolution of Marble from Acid Rain

Dissolution of Marble from Acid Rain

3

Chemical Weathering

Chemical Weathering

��Hydrolysis

Hydrolysis

��In hydrolysis a m

olecule is split into two parts by reacting wit

In hydrolysis a m

olecule is split into two parts by reacting with water.

h water.

One product includes an O

HOne product includes an O

H--from the water molecule, whereas H

from the water molecule, whereas H

++is

is

added to another

added to another

��Mg

Mg22SiO

SiO

44+ 4H

+ 4H

+++ 4OH

+ 4OH

--⇌⇌

2Mg

2Mg2+

2+(aq)

(aq)+ 4OH

+ 4OH

--+ 4H

+ 4H

44SiO

SiO

44(( aq

aq))

��Hydrolysis of

Hydrolysis of olivine produces a solution

olivine produces a solution(m

ineral dissolves)

(mineral dissolves)

��2KAlSi

2KAlSi 33OO

88+ 2H

+ 2H

22CO

CO

33+ 9H

+ 9H

22O

O ⇌⇌

Al

Al 22Si

Si 22OO

55(O

H)

(OH) 44

+ 4H

+ 4H

44SiO

SiO

44(( aq

aq))+ 2K

+ 2K

+++ 2HCO

+ 2HCO

33--

��Hydrolysis of

Hydrolysis of KK-- feldspar produces

feldspar produces kaolinite

kaolinite(clay product)

(clay product)

��What would happen to

What would happen to albite

albiteor or anorthite

anorthitedue to hydrolysis?

due to hydrolysis?

��What would happen to a granite in warm and wet environments?

What would happen to a granite in warm and wet environments?

��Where do the dissolved ions (e.g., Mg

Where do the dissolved ions (e.g., Mg2+2+, K, K++) go?

) go?

++

++

→+

+)

(4

48

10

44

28

34

4)

(4

84

aq

KSiO

HOH

OSi

Al

HO

HO

KAlSi

++

++

→+

+)

(4

48

10

44

28

34

4)

(4

84

aq

KSiO

HOH

OSi

Al

HO

HO

KAlSi

++

++

→+

+)

(4

48

10

44

28

34

4)

(4

84

aq

KSiO

HOH

OSi

Al

HO

HO

KAlSi

SilicicAcid

(Dissolved Silica)

Chemical Weathering

Chemical Weathering

��Oxidation

Oxidation

��4FeS

4FeS

22+ 15O

+ 15O

22+ 22H

+ 22H

22O

O →→

4FeO(O

H) + 8SO

4FeO(O

H) + 8SO

4422--+ 16H

+ 16H

++

��Oxidation of pyrite to form

lim

onite

Oxidation of pyrite to form

lim

onite

��4 FeSiO

4 FeSiO

3(s)

3(s)+ O

+ O

2(g)

2(g)+ 8H

+ 8H

22O

O →→

2Fe

2Fe22OO

3(s)

3(s)+ 4H

+ 4H

44SiO

SiO

4(aq)

4(aq)

��Oxidation and hydrolysis of pyroxene to form

hematite

Oxidation and hydrolysis of pyroxene to form

hematite

��What color will a mafic igneous rock become as it weathers at th

What color will a mafic igneous rock become as it weathers at the e

surface?

surface?

��What will happen to a granite that contains pyrite as it weather

What will happen to a granite that contains pyrite as it weather s s

at the surface?

at the surface?

Oxidation of Pyrite in Sandstone

Oxidation of Pyrite in Sandstone

Oxidation Rind in Sandstone Cobble

Oxidation Rind in Sandstone Cobble

4

Bowen

Bowen’’ s Reaction Series

s Reaction Series

and Chemical Weathering

and Chemical Weathering

Which m

inerals will be m

ost resistant to chemical weathering processes?

Chemical Weathering

Chemical Weathering

Start with feldspars and Fe-bearing

silicates…

End with clays, lim

onite, hematite,

and a loss of Si, Ca, Na, and K into

solution

Sedim

entary Processes

Sedim

entary Processes

��Weathering

Weathering

��Transport

Transport

��Movement of sedim

ents from environments of

Movement of sedim

ents from environments of

relatively high potential energy

relatively high potential energy

��Moved by w

ind or water

Moved by w

ind or water

��Sorted and stratified

Sorted and stratified

��Relatively fine

Relatively fine-- grained (sand by air; pebbles by water)

grained (sand by air; pebbles by water)

��Moved by glacier or gravity flow

Moved by glacier or gravity flow

��Unsorted and

Unsorted and unstratified

unstratified

��Clay to boulders

Clay to boulders

��Deposition

Deposition

��Diagenesis

Diagenesis

Sorted

Sorted vs

vsUnsorted Sedim

ents

Unsorted Sedim

ents

5

Sedim

entary Processes

Sedim

entary Processes

��Weathering

Weathering

��Transport

Transport

��Deposition

Deposition

��Settling

Settling

��Sedim

ent grains stop m

oving when there is insufficient

Sedim

ent grains stop m

oving when there is insufficient

energy to m

ove them farther

energy to m

ove them farther

��Precipitation

Precipitation

��Growth of new m

inerals from oversaturated water

Growth of new m

inerals from oversaturated water

��Diagenesis

Diagenesis

Graded

Graded

Bedding

Bedding

(Fining Up)

(Fining Up)

Deposition by Precipitation

Deposition by Precipitation

(Chemical Sedim

ents)

(Chemical Sedim

ents)

��Norm

al seawater has a salinity of 35g/kg

Norm

al seawater has a salinity of 35g/kg

��Only 6 ions comprise 99% of the ions dissolved in seawater:

Only 6 ions comprise 99% of the ions dissolved in seawater:

��Cl

Cl--

55.04 wt%

55.04 wt%

��Na

Na++

30.61 wt%

30.61 wt%

��SO4

SO422--

7.68 wt%

7.68 wt%

��Mg

Mg2+

2+

3.69 wt%

3.69 wt%

��Ca

Ca2+

2+

1.16 wt%

1.16 wt%

��KK++

1.10 wt%

1.10 wt%

��Marine precipitates will be composed of these ions.

Marine precipitates will be composed of these ions.

��What minerals form as marine precipitates?

What minerals form as marine precipitates?

��Where did K, Na, Ca, and Mg come from?

Where did K, Na, Ca, and Mg come from?

��Why is Fe not abundant in seawater?

Why is Fe not abundant in seawater?

Deposition by Precipitation

Deposition by Precipitation

(Chemical Sedim

ents)

(Chemical Sedim

ents)

6.15

6.15

NaCl

NaCl

Halite

Halite

7.38

7.38

CaCl

CaCl 22●●6H

6H

22OO

-----

-----

0.001

0.001

MgCO

MgCO

33Magnesite

Magnesite

0.0154

0.0154

CaSO

CaSO

44●●2H

2H

22OO

Gypsum

Gypsum

0.00014

0.00014

CaCO

CaCO

33Calcite

Calcite

Solubility (mol/l)

Solubility (mol/l)

Composition

Composition

Mineral

Mineral

Why is CaCl

CaCl 22●●6H6H22O not a naturally occurring

O not a naturally occurring evaporite

evaporitemineral?

mineral?

6

Chemical Sedim

ents

Chemical Sedim

ents

��Lim

estone are the m

ost common chemical

Lim

estone are the m

ost common chemical

sedim

ent

sedim

ent

��Common in shallo

w, tropical, m

arine

Common in shallo

w, tropical, m

arine

environments

environments

��Evaporites (deposits of gypsum and halite)

Evaporites (deposits of gypsum and halite)

are restricted to hot, arid environments

are restricted to hot, arid environments

where evaporation rates are high

where evaporation rates are high

Lim

estone R

eef and Lagoon

Lim

estone R

eef and Lagoon

Fossiliferous Lim

estone

Fossiliferous Lim

estone

Salt Lake D

eposits (Death Valley)

Salt Lake D

eposits (Death Valley)

7

Sabka

Sabka(Saudi Arabia)

(Saudi Arabia)

Gypsum Beds in Red Sandstone

Gypsum Beds in Red Sandstone

Diagenesis: Cementation

Diagenesis: Cementation

��Precipitation of minerals from solutions in pore water

Precipitation of minerals from solutions in pore water

��Composition of ground water varies greatly depending

Composition of ground water varies greatly depending

on such variables as bedrock composition and rainfall

on such variables as bedrock composition and rainfall

��Calcite and dolomite might develop in hard

Calcite and dolomite might develop in hard-- water areas

water areas

��Clays and quartz might develop in soft

Clays and quartz might develop in soft-- water areas

water areas

��Limonite and hematite may occur in rocks that are rich in iron

Limonite and hematite may occur in rocks that are rich in iron

��Pyrite may occur in rocks where the pore waters were anoxic

Pyrite may occur in rocks where the pore waters were anoxic