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Stratigraphy – study
and correlation of
layered rocks
 We interpret
stratigraphy using a
stratigraphic
column
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
Senior Professional Workshop – November 2011
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Principle of superposition
Principle of original horizontality
Principle of lateral continuity
Principle of cross-cutting relationships
Principle of components

Sediment is deposited in horizontal layers
Principle of Lateral Continuity
 Layers may later be uplifted
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
Oldest strata lie at the bottom, and higher
strata are progressively younger
Strata extend continuously in all directions
until it thins
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
A feature that cuts another rock body is
younger than the one being cut
Deposition is not continuous over time
Unconformities are gaps in the stratigraphic
record in which:
1) no sediment was deposited
or
2) sediment was eroded away

Fragments within a rock are older than the
rock they are enclosed in
Nonparallel strata separated by erosional surface
Erosion
 Faults – rock breaks;
Fold
displacement occurs
 Folds – rock bends; does not
break
Fault
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Parallel strata separated by an erosional surface
Sedimentary
Erosion
Sedimentary
Sedimentary rocks rest on older igneous rocks
Sedimentary
Igneous
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Lithostratigraphy – using rock type to correlate
units
Biostratigraphy – using index fossils to
correlate units
 Based on the Principle of Faunal Succession
 Fossils succeed each other in order (oldest at
bottom)

Correlation
based on age

Use measured
ages to
determine
relative ages
Characteristics of index fossils:
1. Abundant
2. Easily recognized
3. Geographically widespread
4. Lived in many types of environments
5. Lived during a short period of time
Deposition rate varies
Unconformities represent missing strata
Radiometric ages needed for
chronostratigraphy
4. Must have appropriate index fossils
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
Using stratigraphic principles, we can
determine the logical order (sequence) of
geologic events
Youngest _____
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Oldest _____
Youngest _____
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Oldest _____
Youngest _____
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Oldest _____
Youngest _____
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Oldest _____
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