Identification of gypsum karstification using an electrical resistivity tomography technique: The case-study of the Sivas gypsum karst area (Turkey)

The Sivas district is the most important gypsum karstified area in Turkey. The oldest evaporites in the region were formed during the sedimentation process of the Oligocene period. Generally, these units extend along the southern part of the Sivas basin. After the Early Miocene Sea drained from this region, extensive evaporite deposition developed. An electrical resistivity tomography (ERT) study was carried out between the Hafik and imranli districts of the Sivas gypsum karstified area. In this research, the prior aim was to determine the general characterization, geometry, sedimentary cover and resistivity properties of gypsums. In addition, the study includes the synthetic modelling of different gypsum karstification types. The evaluation and interpretation were based on ERT data that was collected from the Hafik-imranli region. First, the different karstifications were identified, together with the characteristic features of gypsum in the area. The ERT studies showed that there are large and old karst structures between the Hafik and Zara district. However, the karst structures that are located between the Zara and irnranli regions were interpreted as smaller and younger. The characteristics of both of the regions are different in terms of the morphometric properties. It is certain that the Kizilirmak River has an important impact on the formation of these structures. ERT studies have shown that the cover-and bedrock-type collapse sinkholes are very spread out across the area, and their geometries are different. Throughout time, the suffosion type of cavities formed inside the cover-type sinkholes as a consequence of geological and geomor-phological events. The ERT sections showed that certain parts of these structures collapsed, and then alluvial materials filled in. The shallow groundwater level in the drilling results and the conductive zone in the ERT results are compatible with each other. ERT studies clearly determined the various karstification typologies of gypsums in the region, which also contributed to the creation of a detailed conceptual geological model

Application of the self-potential method to archaeological prospection: Some case histories

The self-potential (SP) method is very rarely used in archaeological prospection because related phenomena are not very well known. The aim of this study is to discuss the different SP phenomena that might be observed at archaeological sites, and therefore the SP method was applied at different archaeological sites in Anatolia (Turkey), such as Acemhöyü k, Amorium, Burgaz and Ulucakhöyük archaeological areas and the Sinop amphorae workshop site. These studies indicated that SP anomalies existed over both burned or unburned materials at archaeological sites, such as walls, pits, kilns, etc. Furthermore, SP anomalies were also found over areas of complex soil distribution and visible physical changes on the surface. Other kinds of SP anomalies were also observed in those archaeological structures located very close to the coastline. These results were confirmed by archaeological excavations, which were carried out after geophysical surveys in the areas studied. All the studies supported that electrokinetic and electrochemical potentials might be the main cause of SP anomalies in the buried archaeological structures. The SP data collected with the gradient and total measurement techniques were processed by forward and inversion methods, and the main SP parameters (h, Q and x0) were determined. In addition, the SP results were compared with other applied geophysical methods such as resistivity and magnetic. © 2004 John Wiley & Sons, Ltd