Where to begin?
First, ask yourself "How Big?"
A geologist can look at rocks as closely as he or she wants
to answer the questions that he or she is interested in asking. Sometimes
it's important to describe a section of rock and the changes that occur
over just a few centimeters. Other times, it may only be necessary to
make very general observations. In this case, subtle changes in the rock
exposure or well log you are studying may be ignored, and a very general
stratigraphic column may be prepared. This also makes sense if you are
describing a large area. Think about it this way - if you were attempting
to understand the stratigraphy of the Grand Canyon, you wouldn't waste
time observing the rock column meter by meter by meter by meter by.........you'd
be there forever! Therefore, you'd be more likely to look for changes
in the rock that were much more obvious.
|You want to describe the stratigraphy of these
rocks by making observations every centimeter? Good luck - you'll
be there for a lifetime! Better think of another plan.
However, if you were trying to understand under what conditions
the Coconino sandstone, one of the rock units seen at the Grand Canyon,
was deposited, you'd be wise to look much more closely at this 100 meters
(300 feet) of rock outcrop. In this case, it makes sense that you would
note changes that occur over small intervals, because your scope would
be much smaller. Changes in rock type that occur over a very small distance
would be much more important to you.
Want to see an example
of a stratigraphic column?