The Grand Canyon - Geologic History
• 1.8 - 1.6 Ga - parts of continents converge
• Mountains Form - sea floor sedimentary rocks deeply buried - Vishnu
Schist
• Igneous intrusions- Zoroaster Granite
• Basement rocks
The Grand Canyon - Geologic History
• Mountains are eroded - 0.5 Ga passes before sediments are again deposited
• 1.2 Ga - sediments that become the Grand Canyon Group are deposited
The Grand Canyon - Geologic History
• 600 Ma - extension produces fault-block mountains
• GC group preserved in low-lying areas
• Tilting and folding
The Grand Canyon - Geologic History
• 500 Ma - following a period of erosion - layers of sediments deposited
in marine and continental systems throughout the Paleozoic, Mesozoic, and into
the Cenozoic
The Grand Canyon - Geologic History
• 45 Ma - Laramide Orogeny
• Kaibab Uplift - Colorado Plateau
• Younger rocks eroded
The Grand Canyon - Geologic History
• 5 -7 Ma Gulf of California opens
• Colorado River system integrates and begins to cut down
• Why?
Types of Stream Erosion
• 1. headward erosion
• 2. Downcutting
• 3. lateral erosion
Stream erosion has limits
• Base Level
• => the downward limit of stream erosion:(downcutting)
• => two types 1) local; and 2) ultimate
•
• Local or Temporary base level = lakes, waterfalls
•
• Ultimate Baselevel = sea level
The Grand Canyon - Geologic History
• 1 Ma volcanic eruptions - lava flows
• Lava dam - quickly breached