1. Sedimentary Petrology GEO 333
Lab (3)
Clastic Sedimentary Rocks
(Classification & Description)
2009
Mansour Al-Hashim

2. Preview of Lab 2 Classification in general
Classification of sedimentary rocks
Clastic sedimentary rocks
Chemical and biochemical sedimentary rocks
Fundamental constituents of sedimentary rocks

3. Objectives of Lab 3 Textures of sedimentary rocks Grain size
Roundness and sorting
Maturity
Color
Cohesiveness (firmness)
Mineral composition and sedimentary structures
Framework and matrix
Cements in sedimentary rocks

4. Textures of Sedimentary Rocks
Sedimentary rocks may have
1. Clastic (fragmental) texture
Grains are stuck together.
Characteristic of clastic sedimentary rocks.
Examples: sandstone and conglomerate.
2. Non-clastic (crystalline) texture
Interlocking crystals.
Characteristic of chemical sedimentary rocks.
Examples: limestone, dolomite, and chert.

5. Clastic (fragmental) Texture
From eos.ubc.ca

6. Non-clastic (crystalline) Texture
From eos.ubc.ca

7. Grain Size (1) Grain sizes can be determined by:
Direct measurement with calipers or meter sticks.
For particles larger than several centimeters.
Screening and petrographic microscope.
For particles from 2 mm to about 1/16 mm.
Pipette or hydrometer (settling rates in water)
For particles less than 1/16 mm.

8. Grain Size (2)
Results of grain-size analysis can be demonstrated as histograms, cumulative curves, or frequency curves.
Many statistical parameters can be calculated (e.g., median, mean, skewness, kurtosis, etc.).
Used to characterize depositional processes and depositional environments.
Udden-Wentworth grain-size scale is the most widely used.

9. Wentworth grade scale

10. Modified Udden-Wentworth grain-size Scale

11. Simplified grain-size scale

13. Roundness and Sorting Roundness (angularity) Sorting
Indicates how smooth or sharp the edges and corners of particles are.
Usually measured with reference to a comparative chart (the commonest is Powers’ , 1953).
Sorting
The degree of uniformity of grain sizes.

14. Categories of roundness
From Tucker (2001)

15. Degrees of sorting
From Compton (1962)
* Note the standard deviation values between classes

16. Visual estimation of sorting
From Tucker (2001)

17. Maturity
Depends on how many cycles of erosion and redeposition the components of a rock have undergone.
There are two types of maturity:
1. Compositional maturity
Compositional maturity = quartz + chert / feldspars + rock fragments.
2. Textural maturity
Textural (structural) maturity = sorting and roundness of sand-sized grains.

18. Textural Maturity
From Folk (1951)

19. Color
Organic matter, sulfides, and some iron oxides give rocks a dark color.
Indicating deposition in a reducing environment.
Some iron oxides give rocks red or yellowish color.
Indicating deposition in an oxidizing environment.

20. Color Indications Black - organic matter FeS
Yellowish - pyrite, markasite FeS2
Yellowish or bluish - sulphates, carbonates, and chlorides
Yellowish to brownish - limonite, goethite FeO(OH)
Reddish - iron oxides FeO

21. From eos.ubc.ca

22. Cohesiveness (firmness)
The degree to which the particles stick together.
Cohesiveness can be described as:
Fragile
Soft
Intermediate
Hard
Very hard

23. Mineral Composition The most common minerals in sedimentary rocks are:
Quartz
Clay minerals
Feldspars
Carbonates (calcite and dolomite)
Rock fragments
Small amounts of amphibole, pyroxene, and mica.

24. Sedimentary Structures
Some common sedimentary structures include:
Bedding (stratification)
Lamination
Graded Bedding
Cross-Bedding
Ripple Marks
Mud Cracks
Raindrop Impressions
Nodules, concretions, geodes, and Stromatolites.

26. Framework and Matrix
The grains in a sand-sized or coarser grained sedimentary rock are known as the framework.
These grains are either:
In contact with each other
Surrounded by empty spaces (pore spaces)
Surrounded by finer grained sediment (matrix)
Cemented together by a bonding material (cement)

27. Framework and Matrix
From Immenhauser (2002)

28. Cements in Sedimentary Rocks
The most common cements in sedimentary rocks are:
Silica (quartz, opal, or chalcedony)
Carbonates (calcite, dolomite, or siderite)
Iron oxides (hematite)
Recognition of matrix and cement is not always possible in hand specimens.

29. Assignment 3

30. References Compton, 1962. Manual of field geology.
Folk, Petrology of sedimentary rocks.
Folk, Stages of textural maturity in sedimentary rocks: Journal of Sedimentary Petrology, v. 21.
Immenhauser, Sedimentology for master students.
Tucker, Sedimentary petrology: an introduction to the origin of sedimentary rocks. Blackwell Science, London, UK.
eos.ubc.ca

31. The End