North American Database of Archaeological Geophysics

Abstract/Summary:

Project Name: Cahokia Mounds State Historic Site, IL;

Reference: Dalan, R.A. and B.W. Bevan (1998). Directionality of Geophysical Parameters as an Indicator of Cultural and Natural Deposits: Experiments at the Cahokia Mounds Site. Office of Contract Archaeology, Southern Illinois University at Edwardsville, Edwardsville, Illinois. Geosight, Pitman, New Jersey. Submitted to Illinois Historic Preservation Agency, Springfield, Illinois.

Directional contrasts in geophysical parameters may allow a distinction between two different types of soil. Soils which have been deposited by natural processes may have geophysical parameters which are very directional. Soils which have been moved by humans may be a jumbled mixture; for these soils, the geophysical parameters may vary little with direction, although they may vary markedly with location.

This hypothesis was tested at the Cahokia Mounds State Historic Site in Collinsville, Illinois, but it was not found to be true in the area of this experiment. The study took place in an area known as the West Borrow Pit Group, located to the southwest of the Grand Plaza. This experiment was done with several different geophysical techniques, including electrical resistivity sounding, an electrical resistivity pseudosection, electromagnetic conductivity, and seismic refraction. It was expected that the anisotropy on and near the mounds would be very low, while it would be higher distant from the mounds in areas where naturally-deposited soils occur. This was not the case. It was also expected that the directions of anisotropy off the mounds or deeper underground within similar deposits would be about the same; this also was not true.

Since these tests have only been made in a part of one site, it also cannot be certain that the method may not be valid at other locations. This has simply been the first test of this approach and there are improvements which might help future work.

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