1 / 32

Sedimentary Petrology GEO 333

Sedimentary Petrology GEO 333. Lab (5) Grain Morphology (Grain Shape) 2009. Mansour Al-Hashim. Preview of Lab 4. Classification of sediments Reading a ternary diagram Finding Clay : Silt Ratio Finding Mud : Sand Ratio. Objectives of Lab 5. Principle axes of sedimentary particles

richardsdavis
Download Presentation

Sedimentary Petrology GEO 333

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Sedimentary PetrologyGEO 333 Lab (5) Grain Morphology (Grain Shape) 2009 Mansour Al-Hashim

  2. Preview of Lab 4 • Classification of sediments • Reading a ternary diagram • Finding Clay : Silt Ratio • Finding Mud : Sand Ratio

  3. Objectives of Lab 5 • Principle axes of sedimentary particles • Grain shape • Roundness • Sphericity • Form

  4. Principle Axes of Sedimentary Particles • Each sedimentary particle has three main axes: • L (a): Long axis • I (b): Intermediate axis • S (c): Short axis

  5. Principle Axes of Sedimentary Particles From Cheel (2005)

  6. Principle Axes of Sedimentary Particles From Cheel (2005)

  7. Grain Shape (1) • Shape is a fundamental property of particles. • May provide important information about the history of sediments. • The three shape properties are: Roundness, Sphericity, and Form.

  8. Grain Shape (2) Grain shape depends on: 1) The original shape of the particle. Mica particles are usually flat, whereas quartz grains are rounded. 2) The internal structure and hardness. 3) The length of transportation (distance of source area). The longer a grain is transported, the more round it becomes.

  9. Roundness (angularity) • A description of the degree of sharpness of the corners and edges of grains. • Gives information about the distance of transport, the energy of transporting mechanisms, and the cycles of erosion and redeposition. • The simplest way to determine the roundness is by visual comparison with standard forms. • The most widely used chart for roundness is Powers’ chart.

  10. Powers’ visual comparison chart Roundness classes After Pettijohn et al. (1973)

  11. Wadell’s Roundness (Rw) • The most accurate method, but it involves the greatest effort and time. • Rw is the ratio of the average radii of curvature of the corners of a grain to the radius of the largest inscribed circle within the particle. • The maximum possible value of Rw is 1.

  12. Wadell’s Roundness (Rw) N : number of corners R : radius of the largest inscribed circle within the particle From Cheel (2005)

  13. Sphericity • The degree to which a particle resembles a sphere. • May be useful for understanding other properties of the particle (e.g. settling velocity) • Stoke’s Law of Settling applies accurately only to spherical particles, and its error increases as the sphericity decreases. • Normally given the symbol “ψ”

  14. Wadell’s Sphericity (ψ) Wadell Operational Sphericity (WOS). Wadell (1932)

  15. Sneed and Folk Sphericity (ψP) • Also known as maximum projection sphericity (MPS). • The most widely-used expression of sphericity. Maximum Projection Sphericity (MPS). Sneed and Folk (1958)

  16. Note • Calculating ψ and ψP requires the measurement of dS, which is impractical for sand-size sediments.

  17. Riley Sphericity (ψR) • Riley sphericity relies on measurements that can be taken from the two-dimensional view of a sand grain as seen through a microscope.

  18. Riley Sphericity (ψR) From Cheel (2005)

  19. Corey Shape Factor (S.F.) • Very similar to MPS. • Widely used by engineers to describe the overall shape of grains Corey Shape Factor (CSF). Corey (1949)

  20. Form • The geometric form of detrital grains, and is expressed using specific terms. • The two commonly used methods of describing the form of particles are based on the ratios of dL, dI, and dS. 1- Zingg diagram (1935) 2- Sneed and Folk classification (1958).

  21. Zingg Diagram From Cheel (2005)

  22. Figure by MIT OCW

  23. Sneed and Folk classification of grain form (1958) From Cheel (2005)

  24. Illenberger Form Diagram 1991 From Illenberger (1991)

  25. Summary Chart

  26. Quiz • Find the form, MPS, and CSF for the following grains • Grain 1: L= 56, I= 49.5, S=39 (mm) • Grain 2: L= 46, I= 36, S= 13 (mm)

  27. Assignment 5 (1) Determine the roundness and Riley sphericity of the given grain. From Folk (1974)

  28. Assignment 5 (2) Using a caliper, measure the L, I, and S axes of the given grains then complete the above table.

  29. References • Cheel, R.J., 2005. Introduction to clastic sedimentology, Department of Earth Sciences, Brock University, Ontario, Canada. • Folk, 1974.Petrology of sedimentary rocks. • Pettijohn F. J., Potter, P.E. and Siever, R., 1973. Sand and sandstone, pp. 617. Springer-Verlag, Berlin. • Illenberger, W.K., 1991. Pebble shape (and size!). Journal of Sedimentary Petrology, v. 61, p. 756–767.

  30. The End

More Related