Chapter 8. Geological Structures, Part B: Folds, Faults, and Unconformities
Introduction
In this chapter you will apply what you’ve learned about structural cross-sections to examining more complex structures on geological maps. Understanding geological structures is important for engineering purposes and safety considerations, as was the case with the Vajont Dam disaster, but some geological structures can also tell us about the forces that have acted on Earth’s crust in the past. The structures can also tell us about conditions at the time those forces were acting. Folds—when fragments of Earth’s crust bend without breaking—indicate that the rocks being deformed were deeper in Earth’s crust and subject to higher pressures and temperatures. Faults—when rocks break and move relative to each other along that break—are the result of cooler rocks being deformed closer to the surface. Unconformities are buried surfaces that indicate a gap in time. That gap can be the result of a variety of processes that either stopped the formation of new rocks, or eroded away existing ones.
Learning Outcomes
After completing this chapter, you should be able to:
- Interpret a geologic map that shows folds, faults, and unconformities.
- Use block diagrams to illustrate more complex geological structures.
- Create a geologic cross-section that includes folds, faults, and unconformities.
- Understand the types of stress that rocks undergo, and their responses to stress.
- Recognize the different types of folds and faults, and the forces that create them.
Key Terms
- Anticline
- Basin
- Compressional forces
- Dip-slip fault
- Dome
- Horst & graben structure
- Monocline
- Normal fault
- Reverse fault
- Shear forces
- Strain
- Stress
- Strike-slip fault
- Syncline
- Tensional forces
- Thrust fault
- Symbols:
Attributions
Adapted from:
McBeth, J., Panchuk, K., Prokopiuk, T., Hauber, L., & Lacey, S. (2020). Introductory Physical Geology Laboratory Manual, 1st Canadian Ed., Overview of Geological Structures Part 2: Folds, Faults, and Unconformities by J. McBeth, T. C. Prokopiuk, & L. R. Hauber. CC BY-SA 4.0
Deline, B., Harris. R. & Tefend, K. (2015) Laboratory Manual for Introductory Geology, 1st Edition, Chapter 12. “Crustal Deformation” by R. Harris & B. Deline. CC BY-SA 4.0
