Stratigraphy & Correlation. Rock Record: Three major ways of subdividing the geologic record: Stratigraphy & Correlation.

Stratigraphy & Correlation



Rock Record:

• Three major ways of

subdividing the geologic

record:



Rock Units (lithology):

• bodies of rock defined by

their distinctive lithologic

features



Rock Units (lithology):

• must be wide spread.

= mapable.



Divisions of Rock Units:

Group

Formation - fundamental unit

Member

Bed - informal unit


http://www.answersincreation.org/images/grandcanyon_strat.gif

http://www.answersincreation.org/images/grandcanyon_strat.gif

Rock Unit Names are based on:

1) Geographic location(where first described)

and

2) Rock type (lithology)



Rock Unit Names: for example

Blowing Rock Gneiss

Erwin Sandstone

Grand Father Mountain Formation(mixed

lithology)



Characteristics of Rock Unit:

• primarily an environmental indicator. • but environments change position through time.




therefore, boundaries of rock units

do not correspond to time units !!!




• boundaries of rock units

do not correspond to time!!



2. Time Units: (chronology)

• intervals of time

• independent of associated rocks (durations in millions of year).



Division of Time Units:

• Eon Era Period - fundamental unit

Epoch Age



Characteristics of Time Units:

• not equal subdivisions (e.g. not equal divisions of say, 10 million yrs)

• may include more than

one rock type



Characteristics of Time Units:



time interval

3. Time-Rock Units:

• All of the rocks deposited

during a particular interval of time.



Time-Rock Units:



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.



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



Correlation:

• Establishment of an

equivalence between two

rock units.



1. Lithologic correlation:

• determine whether two rock

bodies are (or were) part of

the same rock body.



How?

• physically trace the outcrop





How? distinctive lithologic identity Claystone Limestone

Limestone Shale

Shale Sandstone

Sandstone Conglomerate



How? distinctive lithologic identity Claystone Limestone

Limestone Shale

Shale Sandstone

Sandstone Conglomerate

How? position in a stratigraphic sequence



How? position in a stratigraphic sequence



How? geophysical properties



How? geophysical properties (e.g., radioactivity)



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How? geophysical properties (e.g., radioactivity)



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2. Time correlation:

• Process of determining whether

two rock bodies were deposited

at the same time.



Time correlation: How?

• Radiometric dating (e.g. 14C)

• marker beds (e.g. volcanic ash bed)

• paleomagnetic reversals



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. Rock Record: Three major ways of subdividing the geologic record: Stratigraphy & Correlation.

Documents

boundaries of rock units

bodies of rock

rock bodies

rock body

particular interval

geologic record

rocks depositedduring

thecretaceous period