Relative Time
• Relative Dating = sequence of events through time: establishing order
in with rocks are deposited and subsequently deformed and altered.......…
Relative Time - Principles
Principle of superposition
Oldest layers on the bottom => younger layers near the top
Relative Time - Principles
• law of cross-cutting relationships
• law of inclusions
Unconformities
=> conformable beds or strata = relative continuous deposition => no periods
of erosion or nondeposition (time not represented by strata).......
=> unconformity = the result of periods of erosion and nondeposition = missing
time......
Unconformities
1. Disconformity
layered rocks over layered rocks…….erosion and nondeposition
Unconformities
2. Angular unconformity
layered rocks over tilted rocks………..
Unconformities
3. Nonconformity
layered rocks over crystalline rocks……..
• Recognition = Crucial => time not represented by rock
Unconformities - influence on the rock record
Application - Relative Time
- using the principles of relative time to reconstruct the geologic history
of a complex area
Assignment
• Read Ch. 7
• Do the questions with figures 7.1-7.3, 7.5,7.8, 7.13, 7.14, 7.17