Assessing Feature Function and Spatial Patterning of Artifacts with Geophysical Remote-Sensing Data

Abstract

Magnetic surveys and electromagnetic conductivity surveys were conducted at several sites during the course of field work at the Richland/Chambers Reservoir in north-central Texas between 1982 and 1985. Much of this work was conducted at the Bird Point Island site (41FT201), which was used as a proving ground to test the effectiveness of various remote-sensing techniques. Two devices, a Geometrics proton precession magnetometer and a Geonics Limited EM-38 electromagnetic conductivity sensor were tested. The data produced by the EM-38, although initially successful for locating large archaeological features, were less useful for site interpretation than those yielded by the magnetometer.Replicative experiments were conducted to test hypotheses related to feature function and to identify the sources of magnetism present in features. After an experimental hearth and a pit were created on an off-site area, a magnetic survey was conducted and the results were compared with the magnetic responses obtained from archaeological features. Remarkably similar magnetic responses were observed between the experimental features and certain classes of prehistoric archaeological features. Five-cracked rock, consisting of small fragments of iron-enriched sandstone and ironstone, was identified as the primary source of magnetism.In addition to identifying locations of features, the magnetic data also provided information regarding whether or not features had been subjected to multiple episodes of disturbance and reuse. Episodes of recurrent use were indicated by irregular symmetry and unusual magnetic polarity. Several large pit features, which archaeological evidence indicated had been reused, exhibited anomalies with multiple peaks of strong magnetic highs surrounded in several directions by peaks of weak to moderate magnetic lows. In contrast, hearths and pits lacking archaeological evidence of major disturbance or reuse were associated with anomalies that exhibited the normal dipolar signature associated with cultural features—a strong magnetic high with a strong magnetic low immediately to the north. The results of this study demonstrate that the magnetometer has a great potential for aiding in the interpretation of archaeological features in addition to its traditional use as a tool for identifying feature locations.