USING GRADIOMETER AND GPR DATA TO IDENTIFY AND MAP CULTURAL FEATURES

In cultural resource assessments, geophysical surveys are often limited to identifying and locating anomalies for further investigation. In this study, we apply the facies concept to identify radar anomalies with similar reflection characteristics in order to interpret and map different types of cultural features. In addition, we integrated the GPR data with a gradiometer survey.

The survey was conducted at Site 40BT8 located on the T₁ terrace of the Little Tennessee River. Site 40BT8, based on artifact analysis, has a prehistoric to contact period of Native American occupation. Terrace soils consist of a sandy loam. The site is typically submerged by the Chilhowee Reservoir and was exposed when the reservoir was lowered for maintenance work on the dam. Cultural features exposed on the lakebed were mapped in addition to geophysical surveying as part of a nondestructive archaeology preservation effort. Six rectangular survey grids were set up for GPR and gradiometer data collection. Geophysical data were collected at a 0.5 m transect spacing. GPR-Slice software was used to produce a 3-dimensional model of the GPR data. Surfer contouring software was used to construct gradiometer images.

Four radar facies were interpreted to represent possible cultural features of interest. For example, truncated reflections with a horizontal fill could be storage pits; disrupted reflections are interpreted as possible post holes and high amplitude horizontal reflections are interpreted as potential buried hearths. Three additional facies were identified and attributed to channel fill, metal objects, and unknown features.

The magnetometer data showed circular, rectangular and linear patterns of magnetic anomalies on the terrace. The GPR profile for each magnetic anomaly was reviewed to identify the reflection characteristics (radar facies). These radar facies were then mapped across the terrace. These data were used to target select features for further investigation. This approach provides researchers with a detailed 3-dimensional view that provides temporal information of a site’s human occupation.