Sedimentary Rocks. Classification of Sedimentary rocks

Sedimentary rocks and the rock cycle

1. Sedimentary Rocks
From sediments to rocks
Dr Marcus Matthews

2. Sedimentary Rocks
Sedimentary rocks and the rock cycle
Sedimentary Environments
Facies
Diagenesis
Classification of Sedimentary rocks

3. Sedimentary Rocks and the
Rock Cycle
Weathering – parent rocks decomposed and or
fragmented
Erosion – carries particles away
Transportation – moves particles to new locations
Deposition – particles settle, minerals are
precipitated
Burial – layers of sediment accumulate
Diagenesis – physical & chemical changes that
transform a sediment into a rock
Sedimentary rocks are the product of
several overlapping processes

4. Weathering and Erosion
Yield the Raw Materials
Particles and dissolved substances
+
Clastic sediments Chemical deposits
Cementing materials

5. Weathering and Erosion
Yield the Raw Materials
Transported solid fragments
Boulders to clay
Often called siliclastic
Stable minerals e.g. quartz found unaltered
Less stable minerals e.g. feldspar often absent or partially
altered
New minerals e.g. clay minerals
Mineralogy of sediment reflects intensity of weathering as
well as length and type of transport
Clastic sediments generally accumulate more rapidly than
other types of sediments
Clastic sediments

6. Weathering and Erosion
Yield the Raw Materials
Dissolved products of weathering
Chemical sediments are formed at or near place of
deposition (e.g. rock salt, limestone)
Biochemical sediments contain un-dissolved remains of
organisms (e.g. chalk)
In practice many chemical and biochemical sediments
overlap
Chemical and Biochemical Sediments

7. Transportation and
Deposition
Most particles are transported by currents of water or air
(wind). Rivers annually carry a solid and dissolved sediment load
of more than 20 billion tonnes. Currents in air move material
globally but in much smaller quantities

8. Transportation and
Deposition
Currents sort sediments into different size groups
L.S. Fichter (1993, 2000)
http://csmres.jmu.edu/geollab/fichter/sedrx/simpbasclas.html
Clastic rocks
Chemical & biochemical rocks

9. Transportation and
Deposition
Transportation changes the character of the particles.
The key factors are time, distance and mode of transport.
Transportation results in reduced particle angularity and size

10. Transportation and
Deposition
Example: Clastic particles eroded at the headwaters
of the Missouri River in the mountains of western
Montana take hundreds of years to travel the 2000
miles to the Gulf of Mexico. These particles may be
affected by physical weathering (rounding) as well as
intermittent chemical weathering.
Transportation changes the character of the particles.
The key factors are time, distance and mode of transport.
Transport by glaciers does not result in rounding of
particles. The particles are reduced in size.
Transport by wind rounds and polishes particles.

11. Sedimentary Environments
Type and amount of water (ocean, lake, river, arid
land)
Topography (lowland, mountains, coastal plain,
shallow ocean, deep ocean)
Biological activity (coral reefs, swamps)
A sedimentary environment is a geographic
location characterised by a particular combination of
geological processes.

12. Sedimentary Environments
Continental Environments
Alluvial
Desert
Lake
Glacial
Shoreline Environments
Deltaic
Tidal flat
Beach
Marine Environments
Continental shelf
Continental slope
Organic reefs
Deep-sea

13. Facies
Facies are combinations of sediments or
sedimentary rocks characteristic of a particular
sedimentary environment.
Examples: Alluvial facies and deltaic facies

14. Sedimentary Facies:
Alluvial
The sediments deposited by a meandering river form a
sequence where each bed forms in a different part of the
channel. As the channel migrates they are deposited in sequence
on top of each other. The sequence is cyclic with each cycle
ending in over-bank flooding.
Fining upward
sequence

15. Sedimentary Facies: Deltaic
The river delta is a complex
environment as it involves the
combination of river, tides and wave
action. Channel switching by river
causes delta lobes to be periodically
abandoned resulting in a cyclic
sequence of sediments.
Prograding
delta lobe
Marine shale
Coal (abandonment)
One
delta
cycle
One
delta
cycle
Coarsening
upwards
sequence
Active delta lobe
Abandoned delta lobe

16. Diagenesis
Physical and chemical changes that
transform a sediment into a rock
Mud (clay) Mudstone & shale
Sand Sandstone
Gravel Conglomerate/breccia
Carbonate Limestone & marl
rich muds

17. Diagenetic Processes:
Compaction
10-20% water
50-60% water
Compaction (primarily of muds)
Pressure due to
overburden (burial)
squeezes water out of
pore space.
Particles forced closer
together as pore volume
reduces
Note
Geologists say compaction
Geotechnical Engineers say consolidation
To a Geotechnical Engineer compaction means removal of air
through application of energy

18. Diagenetic Processes:
Cementation
Common cements
Iron oxide
Calcium Carbonate
Clay minerals
Silica
Precipitation of new minerals
Loose sand Cemented sandstone

19. Diagenetic Processes: Re-
Crystallisation
New crystal faces precipitated on existing mineral grains
Loose sand
Example: development of a strong quartzite
through precipitation of silica on original quartz
grains
Cemented sandstone
= same mineral

20. Diagenetic Processes:
Dissolution

21. Classification of Clastic Sedimentary
Rocks
Cobbles 60-200mmm, Boulders >200mm
ClaySiltSand
F
i
n
e
M
e
d
i
u
m
C
o
u
r
s
e
F
i
n
e
M
e
d
i
u
m
C
o
u
r
s
e
Gravel
0.002mm0.06mm2mm60mm
0
.
2
0
.
66
2
0
Breccia
(angular fragments)
Conglomerate
(rounded fragments)
SandstoneSiltstone
Claystone
Shale
Grains visible
with naked eye
Grains visible with
naked eye (course),
with aid of x10 hand
lens (fine)
Grains not visible with aid of
x10 hand lens
Mudrocks

22. Classification of Clastic
Sedimentary Rocks
Major types of sandstone based on mineral/rock
contentQuartzite Arkose Lithic SandstoneGreywacke

23. Classification of Sedimentary
Rocks
Classification of chemical and biochemical
sedimentary rocks
Sediment Rock Composition Minerals
Sand & mud Limestone CaCO
3
Calcite
Siliceous sediment Chert SiO
2
Opal,
Chalcedony
Quartz
Peat, organic matter Lignite, Coal Carbon (Coal)
Organics compounds (Oil)
(Gas)
Biochemical

24. Classification of Sedimentary
Rocks
Sediment Rock Composition Minerals
Evaporite Evaporite Sodium chloride Halite
Calcium sulphate Anhydrite
Gypsum
Iron oxide sediments Iron formation Iron oxide Hematite
Limonite
Iron carbonate Siderite
Formed by diagenesis Dolomite Calcium-magnesium
Dolomite
(Dolostone) carbonate
Phosphorite Calcium phosphate Apatite
Classification of chemical and biochemical
sedimentary rocks
Chemical
o

29. Classification of Sedimentary
Rocks
Classification of chemical and biochemical
sedimentary rocks
Sediment Rock Composition Minerals
Sand & mud Limestone CaCO
3 Calcite
Siliceous sediment Chert SiO
2 Opal,
Chalcedony
Quartz
Peat, organic matter Lignite, Coal Carbon (Coal)
Organics compounds (Oil)
(Gas)
Biochemical
o

30. Classification of Sedimentary
Rocks
Sediment Rock Composition Minerals
Evaporite Evaporite Sodium chloride Halite
Calcium sulphate Anhydrite
Gypsum
Iron oxide sediments Iron formation Iron oxide Hematite
Limonite
Iron carbonate Siderite
Formed by diagenesis Dolomite Calcium-magnesium
Dolomite
(Dolostone) carbonate
Phosphorite Calcium phosphate Apatite
Classification of chemical and biochemical
sedimentary rocks
Chemical
o