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

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Presentation on theme: "Sedimentary Petrology GEO 333 Lab (3) Clastic Sedimentary Rocks (Classification & Description) 2009 Mansour Al-Hashim."— Presentation transcript:

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 in general Classification of sedimentary rocks Classification of sedimentary rocks Clastic sedimentary rocks Clastic sedimentary rocks Chemical and biochemical sedimentary rocks Chemical and biochemical sedimentary rocks Fundamental constituents of sedimentary rocks Fundamental constituents of sedimentary rocks

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

4 Textures of Sedimentary Rocks Sedimentary rocks may have Sedimentary rocks may have 1. Clastic (fragmental) texture Grains are stuck together. Grains are stuck together. Characteristic of clastic sedimentary rocks. Characteristic of clastic sedimentary rocks. Examples: sandstone and conglomerate. Examples: sandstone and conglomerate. 2. Non-clastic (crystalline) texture Interlocking crystals. Interlocking crystals. Characteristic of chemical sedimentary rocks. Characteristic of chemical sedimentary rocks. Examples: limestone, dolomite, and chert. 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. Direct measurement with calipers or meter sticks. For particles larger than several centimeters. For particles larger than several centimeters. Screening and petrographic microscope. Screening and petrographic microscope. For particles from 2 mm to about 1/16 mm. For particles from 2 mm to about 1/16 mm. Pipette or hydrometer (settling rates in water) Pipette or hydrometer (settling rates in water) For particles less than 1/16 mm. 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. 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.). Many statistical parameters can be calculated (e.g., median, mean, skewness, kurtosis, etc.). Used to characterize depositional processes and depositional environments. Used to characterize depositional processes and depositional environments. Udden-Wentworth grain-size scale is the most widely used. 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

12

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

14 Categories of roundness From Tucker (2001) 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. Depends on how many cycles of erosion and redeposition the components of a rock have undergone. There are two types of maturity: 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 From Folk (1951) From Folk (1951) Textural Maturity

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

20 Color Indications Black - organic matter FeS Black - organic matter FeS Yellowish - pyrite, markasite FeS 2 Yellowish - pyrite, markasite FeS 2 Yellowish or bluish - sulphates, carbonates, and chlorides Yellowish or bluish - sulphates, carbonates, and chlorides Yellowish to brownish - limonite, goethite FeO(OH) Yellowish to brownish - limonite, goethite FeO(OH) Reddish - iron oxides FeO Reddish - iron oxides FeO

21 From eos.ubc.ca

22 Cohesiveness (firmness) The degree to which the particles stick together. The degree to which the particles stick together. Cohesiveness can be described as: Cohesiveness can be described as: 1. Fragile 2. Soft 3. Intermediate 4. Hard 5. Very hard

23 Mineral Composition The most common minerals in sedimentary rocks are: The most common minerals in sedimentary rocks are: 1. Quartz 2. Clay minerals 3. Feldspars 4. Carbonates (calcite and dolomite) 5. Rock fragments Small amounts of amphibole, pyroxene, and mica. Small amounts of amphibole, pyroxene, and mica.

24 Sedimentary Structures Some common sedimentary structures include: Some common sedimentary structures include: 1. Bedding (stratification) 2. Lamination 3. Graded Bedding 4. Cross-Bedding 5. Ripple Marks 6. Mud Cracks 7. Raindrop Impressions Nodules, concretions, geodes, and Stromatolites. Nodules, concretions, geodes, and Stromatolites.

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26 Framework and Matrix The grains in a sand-sized or coarser grained sedimentary rock are known as the framework. The grains in a sand-sized or coarser grained sedimentary rock are known as the framework. These grains are either: 1. In contact with each other 2. Surrounded by empty spaces (pore spaces) 3. Surrounded by finer grained sediment (matrix) 4. 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: The most common cements in sedimentary rocks are: 1. Silica (quartz, opal, or chalcedony) 2. Carbonates (calcite, dolomite, or siderite) 3. Iron oxides (hematite) Recognition of matrix and cement is not always possible in hand specimens. Recognition of matrix and cement is not always possible in hand specimens.

29 Assignment 3

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

31 The End


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