Geology Reference
In-Depth Information
Mudcracks:
Mudcracks
are created when a standing body of water, such as a lake,
dries up. The surface of the mud cracks and splits as it dries (see Figure 7-12).
These cracks can be preserved as structures in a sedimentary rock.
Figure 7-11:
Cur-
rent ripple marks.
Figure 7-12:
Mud
cracks.
Sedimentary structures can be useful in determining if a sedimentary rock layer is still in
the position (right-side-up) in which it was originally deposited. Understanding pro-
cesses that create sedimentary structures helps geologists interpret the history of a
rock's formation, as well as the environment at the time it was formed.
Stuck between a Rock and a Hard Place:
Metamorphic Rocks
Metamorphic rocks begin as either igneous, sedimentary, or preexisting metamorphic
rocks and undergo a major change, or
metamorphosis.
The change is caused by high
levels of heat and pressure — levels found deep in the earth's crust, below where sedi-
mentary rocks are formed but not so deep and hot that the rocks are melted into a
magma.
