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?


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