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Stratigraphy & Correlation
Rock Record:
• Three major ways of
subdividing the geologic
record:
Stratigraphy & Correlation
Stratigraphy & Correlation
Rock Units (lithology):
• bodies of rock defined by
their distinctive lithologic
features
Stratigraphy & Correlation
Stratigraphy & Correlation
Rock Units (lithology):
• must be wide spread.
= mapable.
Stratigraphy & Correlation
Stratigraphy & Correlation
Divisions of Rock Units:
Group
Formation - fundamental unit
Member
Bed - informal unit
Stratigraphy & Correlation
Rock Unit Names are based on:
1) Geographic location(where first described)
and
2) Rock type (lithology)
Stratigraphy & Correlation
Stratigraphy & Correlation
Rock Unit Names: for example
Blowing Rock Gneiss
Erwin Sandstone
Grand Father Mountain Formation(mixed
lithology)
Stratigraphy & Correlation
Stratigraphy & Correlation
Characteristics of Rock Unit:
• primarily an environmental indicator. • but environments change position through time.
Stratigraphy & Correlation
Stratigraphy & Correlation
Characteristics of Rock Unit:
therefore, boundaries of rock units
do not correspond to time units !!!
Stratigraphy & Correlation
Stratigraphy & Correlation
Characteristics of Rock Unit:
• boundaries of rock units
do not correspond to time!!
Stratigraphy & Correlation
Stratigraphy & Correlation
2. Time Units: (chronology)
• intervals of time
• independent of associated rocks (durations in millions of year).
Stratigraphy & Correlation
Stratigraphy & Correlation
Division of Time Units:
• Eon Era Period - fundamental unit
Epoch Age
Stratigraphy & Correlation
Stratigraphy & Correlation
Characteristics of Time Units:
• not equal subdivisions (e.g. not equal divisions of say, 10 million yrs)
• may include more than
one rock type
Stratigraphy & Correlation
Stratigraphy & Correlation
3. Time-Rock Units:
• All of the rocks deposited
during a particular interval of time.
Stratigraphy & Correlation
Stratigraphy & Correlation
Time-Rock Units:
Stratigraphy & Correlation
Stratigraphy & Correlation
Time Time-RockEon (Eonothem)
Era (Erathem)
Period System Epoch Series Age Stage
All of the rocks deposited during theCretaceous Period . . .
Belong to the Time-Rock Unit of theCretaceous System.
Stratigraphy & Correlation
Stratigraphy & Correlation
Review: ways to divide the rock record
Rock Units - lithology - can vary in age
Time Units - unequal divisions of time, will have variable rock types
Time-Rock Units - all of the rocks
deposited during a given interval of
time
Stratigraphy & Correlation
Stratigraphy & Correlation
Correlation:
• Establishment of an
equivalence between two
rock units.
Stratigraphy & Correlation
Stratigraphy & Correlation
1. Lithologic correlation:
• determine whether two rock
bodies are (or were) part of
the same rock body.
Stratigraphy & Correlation
Stratigraphy & Correlation
Stratigraphy & Correlation
Stratigraphy & Correlation
How? distinctive lithologic identity Claystone Limestone
Limestone Shale
Shale Sandstone
Sandstone Conglomerate
Stratigraphy & Correlation
Stratigraphy & Correlation
How? distinctive lithologic identity Claystone Limestone
Limestone Shale
Shale Sandstone
Sandstone Conglomerate
How? geophysical properties (e.g., radioactivity)
Stratigraphy & Correlation
Stratigraphy & Correlation
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How? geophysical properties (e.g., radioactivity)
Stratigraphy & Correlation
Stratigraphy & Correlation
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2. Time correlation:
• Process of determining whether
two rock bodies were deposited
at the same time.
Stratigraphy & Correlation
Stratigraphy & Correlation
Time correlation: How?
• Radiometric dating (e.g. 14C)
• marker beds (e.g. volcanic ash bed)
• paleomagnetic reversals
Stratigraphy & Correlation
Stratigraphy & Correlation
3. Biological Correlation:(Based on the Principle of Fossil Succession)
• Rocks with the same fossil
assemblages were deposited
during the same interval in
geologic time.
Stratigraphy & Correlation
Stratigraphy & Correlation
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