1. 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.

2. 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.

3. 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.
… same claystone found in Ogallala, NE some 250 miles away!!
The claystone found in both cities is of the same age.
The claystone found in Douglas, WY is the….

4. A fossil is any evidence of past life.
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.

5. 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 ( 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

6. Correlation by Index Fossils
Location #1
Location #2
Location #3
Location #4
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.
FOSSILS A B
“Which fossil can be considered an index fossil?” C D

7. 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