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