Sediment%20Texture%20Word-1 - III Clastic Textures Chapter...

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III. Clastic Textures – Chapter 3 reading 1. Clastic rocks have three components: Grains, Matrix, Cement 2. What is the difference between grains and matrix ? 3. How does cement differ from grains and matrix? How does it form? When does it form? What are some typical cements? 4. Properties of Sedimentary Particles : Sedimentologic studies from either surface or subsurface information depend on accurate sample description. The interpretation can be no better than the data you gather. Much of what we will discuss this semester is what aspects of sedimentary rocks should be described in the field or lab. The first of these will discuss is SEDIMENTARY TEXTURE which is a function of the size, shape, and arrangement of the particles in sedimentary rocks. We will spend several lectures examining some of the important properties of these sedimentary particles. T WO QUESTIONS : A. G RAIN SIIZE IS THE KEY PROPERTY WHY IS THAT ? W HY IS SIZE IMPORTANT ? B. H OW DO WE MEASURE GRAIN SIZE ?
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2 5. Grain size - Techniques for measuring grain size of a sediment sample or sed rock: Quantitative Qualitative direct measurement - gravel visual comparison (usually use intermediate axis) sieving - fine gravel and sand thin section - sand and silt 6. Grain Size What units do sedimentologists use? a) Could use a metric scale – measure grain size in mm or cm Sedimentologists do use the Wentworth scale - units are in mm And there are descriptive terms to go with the mm measurements b) Phi scale - logarithmic scale; has no units φ = - log 2 (size in mm) Example: 1 mm c) advantages to phi scale: (1) fractions are now whole numbers (2) most commonly encountered grain sizes are positive numbers (3) statistical analysis - graphing and calculations are easier 7. Grain size data – a) if you do a visual comparison in the field, you generally give a grain size range or an
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Sediment%20Texture%20Word-1 - III Clastic Textures Chapter...

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