Reading the Rock Record
Sedimentary rocks are rocks made of particles cemented together. They
can be particles of other rocks like sandstones, clay and mudstones, particles
made by living organisms as limestones are, or particles deposited chemically
like salts and other evaporites.
By looking at physical attributes of the sedimentary rocks you can tell
something about the energy of the environment, climatic conditions, source
of the sediments, how they were transported. Fossils in the rock record
living creatures, ecological relationships, chemical conditions. Correlating
layers localy, regionaly and in the end on a global basis, a relative time
scale was established. Paleomagnetic data and chemical isotopes can also
be correlated to put together a picture of continental configuration, paleoclimate
and ocean chemistry.
The photo above was taken in Glacier National Park in Montana, USA. The
ripple marks here in this case tell you the sediments were washed by waves
going in two directions. The red colour indicates the sediments were exposed
to the air so that iron oxidized.