Investigation of a Bronze Age plankway by spectral induced polarization

Abstract

AbstractThe induced polarization (IP) method was developed originally for ore exploration. The transition from electronic to electrolytic conduction causes strong polarization effects in ores. However, other porous materials also exhibit polarization effects. They are caused by electrochemical processes at the internal interface between the pore fluid and the mineral grains. Although these effects are one to two orders smaller in size, modern IP equipment is able to resolve these phenomena. Spectral induced polarization (SIP) investigates the polarization effect in a wide frequency range. As a SIP measurement has an identical setup to conventional resistivity survey, a multichannel geoelectrical instrument (SIP‐256) was developed that is able to measure both apparent resistivity and the polarization effect using a multi‐electrode array.The Federsee bog near Lake Konstanz with its optimal preservation conditions is of international importance for archaeology. Pile dwelling settlements dating back to the eneolithicum have been revealed. Wood samples of a Bronze Age plankway (1500–1400 BC) were collected and investigated. The astonishing result of the laboratory measurements was that the samples showed a remarkable polarization effect in the classic frequency range of IP. Wood therefore can be regarded as a polarizable material. As a consequence a SIP survey was performed in order to investigate the plankway. The SIP survey was carried out in a frequency range from 1 to 60 Hz, where the maximum polarization effect in the laboratory was observed. Two profiles were measured, one parallel and one perpendicular to the plankway. In contrast to the result of the resistivity measurement, the plankway could be identified by weakly increased polarization effects. Copyright © 2002 John Wiley & Sons, Ltd.