Lecture Notes: Geologic Unconformities

Introduction to Unconformities

• Definition: Unconformities indicate missing time in the geologic record.
  • Causes:
    • No deposition: period where nothing was deposited.
    • Erosion: materials removed from the record and deposited elsewhere.
• Types of Unconformities: Three main types—disconformity, non-conformity, and angular unconformity.
  • General Tip: If unsure, refer to them collectively as "unconformities."

Types of Unconformities

Disconformity

• Description: Two horizontal beds separated by an unconformable surface (erosion or non-deposition).
  • Example: Layers A, B, C flat; top of C eroded and E laid on top.
  • Characteristics: Found between two sedimentary beds.
  • Indicators: Smiley face channels representing past river erosion.

Non-Conformity

• Description: Sedimentary beds overlay an unconformable surface on igneous or metamorphic rocks.
  • Example: Hard rock below, sedimentary beds above.
  • Characteristics: The boundary between differing rock types indicates a non-conformity.

Angular Unconformity

• Description: Flat sedimentary rocks overlay an unconformable surface with angled layers beneath.
  • Causes: Result from tectonic activities (faulting, folding) followed by flat deposition.
  • Example: Vertical layers below with horizontal layers above.
  • Characteristics: Exists between sedimentary rock layers.

Application and Visualization

• Video Explanation: Illustrates processes of sediment accumulation, tectonism, and volcanism over 100 million years.
  • Concepts:
    • Unconformities due to erosion, non-deposition, folding, and faulting.
    • Processes like sediment accumulation, extension, faulting, and volcanic activity.

Assignments and Further Learning

• Video Assignment: Analyze a hypothetical cross section representing geologic processes.
  • Key Focus: Understanding deposition timing, unconformity types, and geologic events.
  • Example: Sorting out complex sequences, understanding relative ages, and identifying geological features.

Practice and Observations

• Field Observation: Encourage identification of unconformities on hikes.
  • Look for: Disconformities, non-conformities, angular unconformities, and other geologic features.

Conclusion

• Preparation: Review definitions and diagrams and apply knowledge in real-world scenarios.
• Next Steps: Complete assignments and engage in field practice to solidify understanding of geologic processes.