نقش چينه شناسي در توسعه كارست درحوضه آبگير چشمه علي دامغان

The effect of stratigraphy on developing karst in catchment area of Cheshme- Ali, Damghan

The study area (Cheshmeh-Ali and its catchment area) is located in 32 km northwest of Damghan. The catchment area is mainly composed of thick-bedded and massive limestones of Lar Formation and thin-bedded limestones and marly limestone of Dalichay Formation. In order to evaluate the effect of stratigraphy on karst development in the above-mentioned formations, the geology, the physical and chemical characteristics of water, and characteristics of input system in catchment area of the spring were studied. On the subject of physical and chemical characteristics of water, the discharge of spring, water temperature, electrical conductivity, pH, and dissolved carbon dioxide were measured in-situ and the major cations and anions measured in the lab. The above-mentioned measurements were carried out monthly during 2005-2006 water-year. According to the insignificant variability of all physical and chemical parameters of water and also the characteristics of the catchment area of the spring (i.e. the absence of important karst geomorphological features such as closed depression, sinkholes, large and deep solutional joints and fractures etc.) it may be argued that the aquifer feeding the Cheshme-Ali karst spring is dominated by diffuse flow system. Such a system in karstic aquifers indicates that the degree of karstification in the study area is low. According to the geology setting in the study area, the stratigraphy is one of the most important reasons for insignificant developing of karst in the catchment area of the Cheshmeh-Ali karst spring. Such that the Dalichay Formation (which is slightly suitable for karstification) is located between the thick-bedded and massive limestones of Lar Formation (which is highly appropriate for developing karst) and the location of spring which results in a gradual groundwater flow from aquifer to the spring. The gradual groundwater flow from aquifer to the spring has prevented the developing of karst in the aquifer.