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

• Published in: Engineering geology Vol. 252; pp. 78 - 98
• Main Author: Drahor, Mahmut Göktuğ
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 26-03-2019
• Subjects: Electrical resistivity tomography; Evaporate; Gypsum karst; Sinkhole; Sivas; Gypsum karst; Sivas; Electrical resistivity tomography; Sinkhole; Evaporate
• ISSN: 0013-7952; 1872-6917
• DOI: 10.1016/j.enggeo.2019.02.019

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 İmranlı 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-İmranlı 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 İmranlı 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 Kızılırmak 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 geomorphological 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.
•This study reveals the importance of Electrical resistivity tomography (ERT) method in the research of gypsum karst.•ERT technique gives general characterization of gypsum karsts such as geometry, depth, dissolution zones, sedimentary covers and electrical properties.•This study also presents a distinctive feature from other ERT studies due to a large number of different resistivity data sets.•The general karst typology of Sivas gypsum karsts was revealed by this study with the aid of the collected two dimensional resistivity data sets.