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Sedimentary Petrology GEO 333

Sedimentary Petrology GEO 333. Lab (3) Clastic Sedimentary Rocks (Classification & Description) 2009. Mansour Al-Hashim. Preview of Lab 2. Classification in general Classification of sedimentary rocks Clastic sedimentary rocks Chemical and biochemical sedimentary rocks

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Sedimentary Petrology GEO 333

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  1. Sedimentary PetrologyGEO 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

  12. Roundness and Sorting Roundness (angularity) • 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.

  13. Categories of roundness From Tucker (2001)

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

  15. Visual estimation of sorting From Tucker (2001)

  16. 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.

  17. Textural Maturity From Folk (1951)

  18. 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.

  19. 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

  20. From eos.ubc.ca

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

  22. 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.

  23. 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.

  24. 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)

  25. Framework and Matrix From Immenhauser (2002)

  26. 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.

  27. Assignment 3

  28. References • Compton, 1962. Manual of field geology. • Folk, 1974. Petrology of sedimentary rocks. • Folk, 1951. Stages of textural maturity in sedimentary rocks: Journal of Sedimentary Petrology, v. 21. • Immenhauser, 2002. Sedimentology for master students. • Tucker, 2001. Sedimentary petrology: an introduction to the origin of sedimentary rocks. Blackwell Science, London, UK. • eos.ubc.ca

  29. The End

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