90's Mr.Bond...

Geology 12

Sedimentary Rocks

Sedimentary rocks allow geologists

to recreate environments of the past

Sedimentary rocks allow geologists to be detectives...

To recreate environments of the past.

This was once...

Sandstone - the Wave, Arizona

...this.

Desert sand dunes

Sandstone and Conglomerate - Zhangye Danxia, China

This was once...

...this.

Rivers and streams

This was once...

Limestone - Halong Bay, Vietnam

...this.

Warm shallow-water marine reef

Sedimentary Rocks Topics:

1. General Information

2. Rounding & Sorting

3. Sediment & Sedimentary Rock Types

4. From Sediment to Rock – Lithification

5. Sedimentary Structures

6. Sedimentary Environments

#1 - General Info

Sediments are produced by Weathering of pre-existing rock...

Via either Physical (Mechanical), Chemical, or Biological

means.

Sediments are Transported:

Wind, Ice, Water = Erosion.

Sediments are Altered during transport:

Sorting, Worn Down / Rounded, Chemical Reactions,

etc)

Sediments are Deposited

Sediments are Buried, Compacted & Cemented into Rock

= = Diagenesis through Lithification

Where Do Sedimentary Rocks Come From?

Lithification = sediment compacted into sedimentary rock through pressure.

Diagenesis = any chemical, physical, or biological change undergone by a sediment after its initial deposition and during and after its lithification.

* Does not include weathering

Includes Biological

Formation of Layers in a Lake Bottom...

Lake Bottom = Low Energy

Environment = Small / Fine Sediments!

Here’s What

They Look Like

as rock!!

#2 – Size, Rounding & Sorting:

Sizes:

Clasts in Matrix:

A close look at one type of sedimentary rock!

Rounding & Sorting:

1. Environment of Deposition

2. Mode & Energy of Transport Medium

3. Distance from Source

4. Composition of Material

ALL determine:

the degree of

Rounding & Sorting!

In short, these factors (and others)

interact in a complex way to

determine:

The Type of Sedimentary Rock!

So by studying a particular

Sedimentary Rock’s

characteristics, we can find

clues about all of these

factors:

Environment of Deposition / Mode of Transport /

Distance from Source / Composition of Material

Sorting:

•SORTING is a measure of the range of grain sizes present.

•Particles become sorted on the basis of density, because of

the energy of the transporting medium.

•High energy currents can carry larger fragments.

•Low Energy currents can carry only small fragments

•As the energy decreases (usually farther from the source)

heavier particles are deposited and lighter fragments

continue to be transported.

•This results in sorting due to density.

Sorting of Sediments provides clues as to:

A) Mode / Energy of Transporting Medium

B) Environment of Deposition

Examples:

•Melting ice deposits poorly sorted/angular sediments.

•Rivers often deposits well-sorted/rounded sediments.

•Beach deposits and wind blown deposits generally show

good sorting & rounding because the energy of the transporting medium

is usually constant.

•Mountain Stream deposits are usually poorly sorted because the

energy (velocity) in a stream varies with position in the stream.

Sediments showing a mixture of grain

sizes (Poorly Sorted) usually results

from such things as:

•Rock falls,

•Debris flows,

•Mudflows, and

•Deposition from melting ice.

…or are very close to the source!

•Poorly sorted?

•Moderately sorted?

•Well sorted?

•Poorly sorted?

•Moderately sorted?

•Well sorted?

•Poorly sorted?

•Moderately sorted?

•Well sorted?

Moroccan tree-climbing goats

Rounding:

•During the transportation process, grains may

be reduced in size due to abrasion.

•Random abrasion results in the eventual

rounding off of the sharp corners and edges of

grains.

•Thus, rounding of grains gives us clues to the

amount of time a sediment has been in the

transportation cycle.

•Rounding is classified on relative terms as well.

Sediments freshly weathered or close to source =

Angular

Sediments Weathered long-ago or far from source =

Well Rounded

See Lab Manual Pg. #159 –Fig. 6.3 For Important Sorting/Rounding Info

•Angular grains?

•Rounded grains?

•Well-rounded grains?

•Angular grains?

•Rounded grains?

•Well-rounded grains?

•Angular grains?

•Rounded grains?

•Well-rounded grains?

These Sediments Are ALL Well Sorted...

Well Rounded

Very Well Rounded

Poorly

Rounded =

Angular

Intermediate Rounding

Gravel Size! Gravel Size! Gravel Size! Sand Size!

Well Rounded & Well Sorted

Poorly Rounded & Well Sorted

Intermediate Rounded & Poor Sorted

Poor Rounded & Intermediate Sorted

Rounding & Sorting Vary Together...

Rounding? Sorting?

Intermediate rounding, poor sorting

How would you describe Rounding & Sorting for this group

of Sediments from an “Outcrop” near Squamish?

How Would you describe

the “Energy” of the

depositing medium?

High Energy

Terminal Moraine

River Close To Glacier

River Further From Glacier

Let’s Interpret

The Information

in This Past

Exam Question!

#3 - From Sediment To RockLithification:

Lithification = Conversion of

Sediments to Rock!

Happens via the process "Diagenesis"

Includes:

1- Burial

2- Compaction

3- Cementation / Precipitation /

Crystallization

1. Burial

Adds pressure.Increases Temperature.

Decreases pore space.Squeezes water out.

Lower beds (1) are buried by successive layers of sediment (2 &3)!

TONS O’ Weight!

2. Compaction

Squeezing of sediments due to added weight of sediments

added on top - results in consolidation.

Squeezes water out of pore spaces between sediments.

Overall pore space between sediments is reduced.

Grains stick together.

Grains align.

Compaction

in Action!!

Burial usually responsible for compaction!

3. Cementation / Precipitation / Crystallization

Gluing of grains together.

Happens via the deposition of materials (usually calcite) between grains.

The materials are dissolved in pore water & precipitate out or crystallize.

Also decreases the pore space and squeezes more water out.

A close up of mineral grains cemented together by CALCITE CEMENT which has precipitated in the pore spaces!

Calcite Cement

Mineral Grains

Porosity and Permeability:

A B

Which image has greater porosity?

Which rock is the

most permeable?

Least permeable?

#4 - Sediment & SedimentaryRock Types:

Three Main Categories of Sedimentary Rocks:

#1- Clastic / Detrital

#2 - Chemical

#3 - Biological

Examples of

Clastic / Detrital

Sedimentary

Rocks:

The size of the clasts

(individual grains)

determine Rock Type for

Clastic Sedimentary

Rocks!

Collectively

called Gravel

Clastic

Collectively

called MudSand

Lab Manual p.164

Gravel!Associated With Very “High Energy” Environments…

-Mountain Rivers, Land Slides, Rivers in Flood, etc...

Rounded Gravel Sized Grains / Clasts

Angular Gravel Sized Grains / Clasts

Associated With “Medium Energy” Environments…

-Sea Shores, Lake Shores, River Banks, etc...

Sand!

Associated With Very “Low Energy” Environments…

-Sea Bottom, Lake Bottom, etc...

Mud!

Clasts Larger Than 256 millimeters = Boulder

&

Between 2 millimeters to 256 millimeters = Gravel

Produce:

Conglomerate if Round

&

Breccia if Angular

Gravel Sized Sediments From Squamish

Boulder & Gravel Sized Sediments From The Mamquam River in Squamish

How Do You Know?

What Type of Sedimentary Rock Would These Produce if They Were Lithified?

Conglomerate

Conglomerate:

Conglomerate:

Breccia:

Breccia:

Breccia...

Clasts between 1/16th of a mm & 2 mm

= Sand

Produce:

Sandstone

Sandstone:

Sandstone:

Sandstone Close-Up:

Arkose Sandstone:

Arkose = red, due to high amount of K-feldspar

Graywake Sandstone:

Graywacke = darker, poorly-sorted angular grains, formed in the ocean, along continental slopes.

Sediments Between 1/256 th of a mm & 1/16th of a mm = Silt

&

Sediments Smaller Than 1/256 th of a mm = Clay

Produce:

MudstonesSiltstone

Claystone

Shale

Siltstone:

Claystone:

GeneralMudstone :

Siltstones and Claystones are

grouped together collectively as:

MUDSTONES.

If a MUDSTONE is 'layered' and

breaks apart in thin chunks (Fissile)

we call it…

SHALE!!

Shale:

Shale:

Shale:

See How The Shale Splits Easily into Layers?In other words the shale is very “Fissile”

Burgess Shale, BC

Shale beds are often rich

in organic materials = fossils

Burgess Shale

Trilobite fossils

Mudstones / Shales have very small clasts

&

therefore have VERY LOW...

Porosity

Permeability

...and because they form in

"Low Energy" environments...

such as lakes or ocean bottoms

lots of "Organic Material"

accumulates in them...

Especially rich in marine microorganisms...

...as a result most oil/natural gas

sources originate from them!

...and are also capped by them!

Marine Shales = Rich In Marine Microorganisms = Oil/Gas Source!

Shales have a

lack of Porosity

& Permeability

= Good Trap

for oil/gas

migrating

upward!

Lab Manual p.164

Examples Of

Chemical

Sedimentary

Rocks:

For Our

Purposes

Consist Mainly of

Evaporites:

Diagram showing development

of a typical

"Evaporite" deposit

such as Gypsum or Halite

Ocean Water = Mineral Rich = Minerals left behind as

chemical precipitates when it evaporates!

Bonneville Salt Flats, Utah

A sedimentary environment that was once a

shallow sea that evaporated…results in

EVAPORITE DEPOSITS!!

Top Gear filming at

Bonneville Salt Flats:

Consists of NaCl precipitated from Water

Halite:NaCl

Halite = Rock Salt

...more Halite!

Gypsum:

Consists of Gypsum precipitated from Water

CaSO4. 2H2O

A Bed of Gypsum:

Chert:

Consists of silica precipitated from Water

SiO4

Chert Close-up:

Consists of Dolomite precipitated from Water

Dolomite (a carbonate, like limestone):

Huge Dolomite

Formations form

the “Dolomite

Mountains” of Italy!

Dolostone (rock containing dolomite)

Dolostone

Ironstone

Consists of Limonite/Hematite precipitated from Water

Examples Of

Biological

Sedimentary

Rocks:

Most Important

Types are

CarbonatesMade of Calcite

(Calcium Carbonate)

CaCO3

Become Limestone:

Limestone :

Much Limestone comes from significant

Biological Contributions such as

coral reefs

or

shells of marine organisms

whose production has involved chemical

reactions...

…in other words it is BIOCHEMICAL!!

Limestone Beds:

Oolitic limestone:

Oolites are tiny concentric

spheres of calcium

carbonate (Calcite) which

range between 0.1 and 2.0

mm in diameter.

Oolites are not

fossils!

They form by the

precipitation of Calcite

under certain conditions in

warm shallow seas.

Travertine = limestone chemically

Precipitated from hot springs

Travertine Terracesin Turkey

Micrite...

Microcrystalline calcite

Limestone (coquina):

Limestone (coquina) Close-up:

Limestone (coquina) Close-up:

Fosilliferous Limestone :

Fosilliferous Limestone Close-Up:

Chalk

Chalk

White Cliffs of Dover,

England

Other Types

Consist of

Mainly

Plant Fragments

Compressed over

Time

COAL

Mostly of Plant & Animal fragments which

have been chemically altered;

Therefore, we can classify it as a

CHEMICAL SEDIMENTARY ROCK with

a significant biological contribution...

…in other words it is BIOCHEMICAL!!

Peat

Bituminous CoalLignite Coal

Peat

Anthracite Coal

COAL...

Bituminous Coal:

A Close Up of Bituminous Coal:

Anthracite Coal:

Most metamorphosed coal, 92-

98% carbon