The Measurement and Analysis of Depth in Archaeological Geophysics: Tests at the Biesterfeldt Site, USA

Abstract

Information on depth may be gained through the analysis of geophysical maps, by utilizing soundings, pseudosections, or time-slices, or via the application of downhole measurements. Various methods and techniques were compared at the Biesterfeldt site, a proto-historic earth-lodge village in the Northern Plains, USA. Both traditional and more experimental approaches were used, including ground-penetrating radar time slices and overlay analyses, a resistivity pseudosection, two-and three-dimensional magnetic and resistivity modelling, and downhole tests of magnetic susceptibility, magnetic viscosity, total magnetic field, capacitance and resistivity. A direct-push colour system, measuring the reflection of light over the red-green-blue (RGB) and near-infrared spectrum, provided another useful tool for mapping the depths of archaeological features and stratigraphic layers. Early historic maps of the site show more than 60 earth lodges and an encircling ditch. Current management efforts aim not only to georeference and evaluate the accuracy of these maps, but to determine the state of preservation of the archaeological features. These efforts are complicated by historic cultivation of the southern half of the site. Geophysical tests focused on depth yielded locations and depths for several lodges and the filled ditch as well as small and thin features and layers within them. A buried soil was also identified. Downhole geophysical and direct-push color techniques were particularly helpful for mapping lodges in the plowed portion of the site. These results were confirmed through excavation. Adding geophysical tests focused on depth at Biesterfeldt provided information useful for understanding feature formation, context, and post-depositional processes, and for designing effective at-surface geophysical surveys, planning excavations and site management. These tests highlight the advantages of integrating techniques focused on depth with geophysical area surveys.

Cutbank Geophysics: A New Method for Expanding Magnetic Investigations to the Subsurface Using Magnetic Susceptibility Testing at an Awatixa Hidatsa Village, North Dakota

“…At the Biesterfeldt Site, a protohistoric earthlodge village located along the Sheyenne River in eastern North Dakota, magnetic enhancement of lodge floors [3] was similar to that at the Sakakawea site. Like Sakakawea, the highest values were associated with ashy areas and associated features (hearths and pits).…”

“…Although no previous subsurface susceptibility studies had been conducted within the KNRI, down-hole and in-excavation susceptibility results from other sites in the Northern Plains had demonstrated the potential of subsurface measurements for detailing earthlodges and other typical features (e.g., [3,43,48,49]). At the Double Ditch site in North Dakota ( [43,48], also summarized in [2]), a prototype Bartington Instruments MS2H down-hole sensor was tested on a subterranean food storage pit, house basin, borrow pit, mound, and paleosol.…”

“…These subsurface geophysical studies can be used to understand exposed features as well as to reveal features invisible to the excavator. Subsurface geophysical surveys, however, have generally been conducted in conjunction with controlled excavations (e.g., [1,2]) or utilized small-diameter corers coupled with down-hole geophysical sensors (e.g., [3]) and thus have not provided broad access to buried cultural features made possible through a cutbank geophysical approach.…”

Technique, analysis routines, and application of direct push-driven in situ color logging

“…The system is a tristimulus colorimeter, which uses the narrow wavelength bands throughout the spectrum to measure the amount of radiation in the visible spectrum (Barrett 2002). We used the CLT (also known as soil color optical screening tool-SCOST TM ) designed by Dakota Technologies Inc., (Fargo, ND, USA) (Dalan et al 2011).…”

“…Viscarra Rossel et al (2006aRossel et al ( , b, 2009 show how to predict organic carbon and other soil parameters from such color records. For geoarchaeological exploration, Dalan et al (2011) derive data on the depth of basal boundaries of houses by in situ-obtained DP colors. They state the method to be a useful application.…”