Karstic Features of Gachsaran Evaporites in the Region of Ramhormoz, Khuzestan Province, in Southwest Iran

Karst and karstic features are a common and well-developed phenomenon that can be seen extensively in the Iranian Plateau, especially in the Zagros Mountains. However, little is known about their occurrence and extension in its evaporitic rocks. One of the very famous evaporitic formations well known in Iran and other countries around the Persian Gulf area is the Gachsaran Formation of Miocene age. Its exposures are largely distributed in the southwestern Khuzestan Province. The study area is located in its central to eastern part and is an area with extensive outcrops of the mentioned formation having some interesting karstic features. Undoutedly, solution processes and tectonic stresses had a key role on their establishment. The area is geologically part of the Zagros simply folded belt that obeys its general NW-SE trend. They are mostly thrusted over the Khuzestan Plain mainly by NW-SE striking thrust faults along the mountain-plain boundary. In the area of study, the formation is composed of anhydrite, red and grey marls, salt and sandy limestone. As a seismotectonically active region, it is significantly affected by few numbers of large and small faults such as Lahbari, Jarreh, Dasht-e Shir and Dasht-e Anar faults. Most of the karstic features such as sink holes, springs and cavities are related to the geologic structures. Direction of the stream courses is also related to them. Due to the incompetency and solubility of the layers, some solution features were formed within small folds. The morphology of the evaporite outcrops reflects the influence of the geologic structure. The important recognized trends are: SW-NE, E-W and NW-SE. This study was the first attempt to define karstification in the Gachsaran Formation with regard to its impact on the quality of surface and ground waters and to its limiting factors. Particularly with regard to the development of dam construction, it is planned that a comprehensive field survey and remote sensing analysis will be done to determine and define all the possible karstic features.