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