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Correlation Correlation is the process of showing that
rocks or geologic
events from different
places are of the
same/similar age.
The dark layers of rock near the top of the butte are of the same age as the the dark layers of rock
seen near the top of the plateau in the
distance. The dark layers of strata had been separated due to
erosion over many years.
Correlation by Exposed Bedrock
The Colorado River has “cut” through layers of sedimentary rock over
time.
One specific layer of rock on one side of the river can be “correlated” with
the same layer on the other side of the river.
Both rock layers would be of the same age.
Correlation by Similarities in Rock
The claystone that makes up the White River Formation is white-pink in color and has a “chalky”
texture to it.
The claystone found in Douglas,
WY is the….
… same claystone found in Ogallala,
NE some 250 miles away!!
The claystone found in both cities is of the
same age.
Fossils
A fossil is any evidence of past
life.
Fossils can take many forms. Bone, teeth,
shells, impressions/mold
of shells, skin impressions, footprints,
permineralized bone and plant material are all
examples of fossils.
Correlation by Index Fossils
An index fossil is evidence of
past life that …
LIVED FOR A SHORT PERIOD
OF TIME
and
CAN BE FOUND OVER A LARGE GEOGRAPHIC
AREA
Index fossils can be useful tools in correlation.
Mucrospirifer is an example of an index fossil.
Mucrospirifer only lived during a period of geologic time known as the Middle Devonian (398-385 mya).
SHORT PERIOD OF TIME
Rocks of Middle Devonian age can be found in areas of western New York to areas as far west as Iowa.
WIDE GEOGRAPHIC AREA
Mucrospirifer
Correlation by Index Fossils
Location #1 Location #4Location #3Location #2
FOSSILS
A B
C D
“Which fossil can be considered an index fossil?”
Exposed strata is seen at four separate locations. Each location is separated by 50 miles. Each layer within the exposed strata is represented by a color. Each colored
layer represents a specific age of geologic time.
Correlation by Volcanic Ash/Meteor Impact
A volcanic eruption may discharge a large
amount of gas and ash into the atmosphere.
A meteoric impact can discharge high
levels of iridium and other rare elements
into the atmosphere.
Volcanic ash and meteor impact debris
can be deposited rather quickly over a
large geographic area.
Like an index fossil, a layer of volcanic
ash/meteoric debris within rock strata can
be used as tool for correlation.
The K/T Boundary is a thin layer of sedimentary rock that is rich in iridium – an
element commonly found in celestial objects (ie: asteroids) but rarely found on Earth.
The K/T Boundary represents a period of geologic time (~ 300,000 yrs.) between the
Mesozoic and Cenozoic Eras.
The K/T Boundary can be found over a wide geographic area.
The K/T Boundary represents the point of dinosaur extinction.
K/T Boundary