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Sedimentary Petrology GEO 333

Preview of Lab 2. Classification in general Classification of sedimentary rocksClastic sedimentary rocks Chemical and biochemical sedimentary rocksFundamental constituents of sedimentary rocks. Objectives of Lab 3. Textures of sedimentary rocksGrain sizeRoundness and sortingMaturityColorCoh

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Sedimentary Petrology GEO 333

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

    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

    6. Non-clastic (crystalline) Texture

    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) 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

    15. Degrees of sorting

    16. Visual estimation of sorting

    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.

    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

    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)

    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, 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

    31. The End

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