Stratigraphic Principles Lecture Notes

Key Concepts

• Stratigraphic Principles: Rules to order geologic events.

Principle of Superposition

• In a series of layered rocks, oldest layer is at the bottom and youngest is at the top.
• Example: Grand Canyon sequence - Tipit sandstone (oldest) to Kaibab formation (youngest).

Principle of Original Horizontality

• Layered rocks are originally deposited horizontally.
• Deformation indicates post-deposition events.
• Example: Vasquez Rocks (tilted due to tectonic events).

Principle of Original Lateral Continuity

• Layered rocks are deposited continuously across a basin.
• Erosion explains gaps in layers.
• Example: Eroded strata showing sandstone and limestone continuity across valleys.

Principle of Cross-Cutting Relationships

• Rocks/features cutting through others are younger.
• Example 1: Sedimentary layers cut by a dike.
• Example 2: Quartz veins and fractures in rock sequence (B is oldest, A next, C youngest).

Principle of Inclusions

• Material included in a rock layer is older than the layer itself.
• Example: Granite chunks in sandstone mean granite is older.
• Considerations for intrusive igneous rocks like granite.

Unconformities

• Unconformities: Gaps in the geologic record due to erosion or non-deposition.
• Disconformity: Horizontal layers above and below with no deformation.
• Angular Unconformity: Tilted/folded rock layers below, flat layers above.
• Non-Conformity: Crystalline rock below, sedimentary rock above.
• Sicker Point, Scotland: Important site for understanding unconformities and deep time.

Significance of Hutton's Work

• Realization of Earth's age and deep time via uniformitarianism principles.
• Understanding the complex history of rock formation, tilting, erosion, and deposition.

Application

• Use these principles to decipher chronological order in geologic history.
• Practice with diagrams and videos to understand the process.

Study and Practice

• Review videos and slides related to these principles.
• Engage in practical exercises during class to apply these principles.