Stratigraphy EASC 422
Principles of stratigraphy
Stratigraphy is the study of rock layers. Rock layers are formed from sediments
deposited by water, wind, ice, and animals. Sedimentary rocks are composed of
particles of minerals and organic matter that were carried by rivers, streams, lakes,
oceans, and glaciers. When sedimentary deposits accumulate over time, they form
layers called strata. Each layer represents a different period in Earth history. By
studying the stratigraphic record, we can learn much about past environments and
events.
The principle of original horizontality
Sedimentary rocks can be found in a variety of configurations, but they are rarely
horizontal and are usually tilted or dipping at various angles, or even folded. They
could not have been deposited in that condition; it is obvious. Sediments in a basin
are always deposited horizontally, regardless of basin shape. Tilting and folding are
structural changes that occur after rocks have been deposited and consolidated. So,
in order to study the rocks, you must imagine them not in their current position, but
as if they were originally deposited horizontally. This is the original horizontality
principle.
Principles of stratigraphy
Stratigraphy is the study of rock layers. Rock layers are formed from sediments
deposited by water, wind, ice, and animals. Sedimentary rocks are composed of
particles of minerals and organic matter that were carried by rivers, streams, lakes,
oceans, and glaciers. When sedimentary deposits accumulate over time, they form
layers called strata. Each layer represents a different period in Earth history. By
studying the stratigraphic record, we can learn much about past environments and
events.
The principle of original horizontality
Sedimentary rocks can be found in a variety of configurations, but they are rarely
horizontal and are usually tilted or dipping at various angles, or even folded. They
could not have been deposited in that condition; it is obvious. Sediments in a basin
are always deposited horizontally, regardless of basin shape. Tilting and folding are
structural changes that occur after rocks have been deposited and consolidated. So,
in order to study the rocks, you must imagine them not in their current position, but
as if they were originally deposited horizontally. This is the original horizontality
principle.
