= 2 ways of dealing with time.…
A. Absolute/Numerical Time
B. Relative Time
Geologic Time Scale
• Concepts of relative and absolute time combined to create =>
• Geologic Time Scale
• Units of time
• Eon, Era, Period
Relative Time
• Relative Dating = sequence of events through time: establishing order
in with rocks are deposited and subsequently deformed and altered.......…
- based on the principle of uniformitarianism
• Steno's and Hutton's Principles:
1. Principle of original horizontality
2. Principle of original continuity
Layers originally continuous throughout a region => erosion
3. Principle of superposition
Oldest layers on the bottom => younger layers near the top
Relative Time - Principles
4. law of cross-cutting relationships
5. law of inclusions
6. Law of Floral/Faunal Succession
=> different groups of fossils succeed one another in the geologic record in a definite and recognizable order.....…the evolutionary clock
William “strata” Smith
=> 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......
1. Disconformity
layered rocks over layered rocks…….erosion and nondeposition
2. Angular unconformity
layered rocks over tilted rocks………..
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
Reconstructing Geologic History
- describe rocks
- establish sequence of events - principles & fossils
- interpret environments = sedimentary facies
Lateral and Vertical Relationship of Facies (Time & Space)
=> Stratigraphy
=> How does this history recorded in these rocks relate to the region
and the rest of the world? - Correlation
Stratigraphic Terminology -
Lithostratigraphy - Units = Group, Formation, Member, Bed
Correlation of stratigraphic units
Types
lithostratigraphic
correlation
similar rock types
Formations
Event Correlation
uses marker beds
ash beds/bentonites
Correlation => Types
Guide Fossils
Properties
occurs during a short interval in time
is easy to recognize and is common
lived in many different places…..
After correlation
- can reconstruct regional changes in environments, sea level,
and climate