Virtual Field Study
Locating Yourself Stratigraphically:
Once you have recorded your observations and measurements at an outcrop you need to
determine where it is stratigraphcially, i.e., where it is in relative geologic time.
This is particularly true if the goal of your study is to examine evolutionary relationships. This section of
the module uses three sample locations along the Calvert Cliffs shoreline to demonstrate
how a composite a stratigraphic column, the synthesis of individual outcrops, is constructed.
The first step in the process is to examine an outcrop to determine what formal rock unit, or formation, you are examining. In our study area, these would be the Calvert, Choptank and St. Mary's Formations and they differ from one another on the basis of grain size, color and assemblages of fossils. In the 19th century, a geologist named George B. Shattuck studied these rocks and recognized that each of these three formations could be further subdivided based on the fossils that are present. These subdivisions are now called "Shattuck fossil zones" and when you can identify the fossils that are present in an outcrop, it is not too difficult to determine which rock unit you are looking at. In addition to using basic field skills, such as recognizing the dip of the rock layers, the fossil zones can be used to correlate, or equate, one outcrop to another. In this fashion we can determine the relative age relationships of the outcrops and ultimately we can synthesize them together to construct a composite stratigraphic column.
Last modified October 06 2008 02:54 PM