Electrical and GPR prospecting at Palo Blanco archaeological site, northwestern Argentina

Abstract

We conducted a geophysical survey at the Palo Blanco archaeological site located in Catamarca, Argentina. Age estimates from radiocarbon dating indicate first occupation of the site around 1500 years ago. The first description of the site was done in 1960. At that time, five residential units with different architectural arrangements were reported. These structures had different levels of deterioration caused by exposure and human activities. Some of these original structures have become completely covered by sediments. To aid in the design of efficient excavation plans, detailed maps are required to locate the buried walls. For this purpose, we conducted geophysical surveys over one of the structures. We had poor documentation about the structure at the time of the survey. Only one of the walls described in the earlier report was partially visible. We used two geophysical methods: ground-penetrating radar ͑GPR͒ and electrical resistivity. We performed 2D inversion of the resistivity data, together with numerical GPR simulations. These helped to distinguish the expected reflection events from others, aiding in a correct interpretation of the data. Finally, we made a complementary interpretation of the resistivity and GPR data to compile a detailed map of the selected structure. We found that considering the two methods independently would have led to an incomplete map. We delineated a much more complex structure than originally expected and designed an excavation plan which was carried out. The layout of the rooms of the structure fully matched the predictions based on the interpretation used in detecting the walls and their depths. In this way, the geophysical forecasts were confirmed after excavation.

GPR prospecting in a prehispanic village, NW Argentina

“…These signals are very similar to the characteristic ones produced by diffraction at the tops of the excavated walls in NH3 (the previously investigated sector); for example, Fig. 3 shows this kind of electromagnetic response (from Martino et al, 2006). The similarities between the detected anomalies and the previously obtained patterns and the repetitive appearance in successive profiles allow us to assume here the presence of a buried wall centered at 14.5 m and directed along the WE direction.…”

“…In 2004 we have began an archaeo-geophysical study in Palo Blanco site, NW Argentina. In the first stage of this study, we obtained a detailed map of one of the buried structures in this site, by applying the GPR and the dipole-dipole methods (Martino et al, 2006). This map made possible an efficient excavation of the structure.…”

“…In a previous work (Martino et al, 2006), a monostatic survey was carried out in the NH3 sector of Palo Blanco and a detailed map of the subsurface was obtained. These investigations confirmed Sempé's descriptions of this residential unit, and also a number of nonreported internal walls were predicted.…”

Two different approaches for georadar data processing: A case study in archaeological prospecting

“…The exploitation of georadar in archaeological applications is very common (Barone et al, 2007;Martino et al, 2006;Abbas et al, 2005;Orlando, 2005;Tallini et al, 2004;Leckebusch, 2003;Piro et al, 2002;Basile et al, 2000;Conyers and Goodman, 1997;Malagodi et al, 1996). The georadar is usually exploited in a configuration, where the receiving and transmitting antennas are separated by a small fixed offset and are moved very close to or in contact with the ground-interface and for each position a time domain trace is collected.…”

Rapid evaluation of multifrequency EMI data to characterize buried structures at a historical Jesuit Mission in Argentina

“…Geoelectrical methods are especially suitable for detailed quantitative analysis since there are many proven 2D and 3D inversion codes available that can produce high-resolution electrical images of the subsoil. This methodology has previously enabled us to characterize different archeological and environmental targets (Osella et al, 2005;Martino et al, 2006).…”