Evolution of noble gas and water isotopes along the regional groundwater flow path of the Konya Closed Basin, Turkey

Noble gas and water isotope compositions of regional groundwater were investigated along two transects in the Konya Closed Basin (KCB) of central Turkey. According to the 3He/4He versus Ne/He plot of samples, crust (up to 86%) and mantle (up to 26%) appear to be the primary and secondary sources of dissolved He in groundwater, respectively. After the beginning of both transects where the flow domain is confined, both 3He and 4He accumulate steadily in groundwater. Thereafter, the intermediate recharge from the surface in the unconfined part of regional flow system disrupts the steady accumulation trend of 3He and 4He. Effect of intermediate recharge on regional groundwater is also indicated by the spatial variations in specific conductance, temperature, water isotopes, and tritium signals. At the last part of the flow domain where the system becomes confined again 3He and 4He start to accumulate in the eastern transect whereas they continue to decline in the western transect probably because of degassing to atmosphere through thinner confining unit. The 4He accumulation rates based on radiocarbon ages and 4He concentrations along both transects between the mountain flank and Obruk Plateau are in agreement with literature values but differ from each other. The accumulation rate along the eastern and western transects are 4.93 × 10-11 cm3 STP/g•year and 1.99 × 10-10 cm3 STP/g•year, respectively. These values reveal that the 4He accumulation rates may differ at least four times at different parts of a single aquifer, which are located 30 to 60 km apart. It is understood that any groundwater age-dating attempt by 4He requires a firm pre-assessment of spatial 4He accumulation rates. He isotope signal in the groundwater of KCB proves the mantle and/or crustal gas input into the carbonate aquifer in which an on-going hypogenic karst development has been suspected

Evolution of noble gas and water isotopes along the regional groundwater flow path of the Konya Closed Basin, Turkey

Noble gas and water isotope compositions of regional groundwater were investigated along two transects in the Konya Closed Basin (KCB) of central Turkey. According to the 3He/4He versus Ne/He plot of samples, crust (up to 86%) and mantle (up to 26%) appear to be the primary and secondary sources of dissolved He in groundwater, respectively. After the beginning of both transects where the flow domain is confined, both 3He and 4He accumulate steadily in groundwater. Thereafter, the intermediate recharge from the surface in the unconfined part of regional flow system disrupts the steady accumulation trend of 3He and 4He. Effect of intermediate recharge on regional groundwater is also indicated by the spatial variations in specific conductance, temperature, water isotopes, and tritium signals. At the last part of the flow domain where the system becomes confined again 3He and 4He start to accumulate in the eastern transect whereas they continue to decline in the western transect probably because of degassing to atmosphere through thinner confining unit. The 4He accumulation rates based on radiocarbon ages and 4He concentrations along both transects between the mountain flank and Obruk Plateau are in agreement with literature values but differ from each other. The accumulation rate along the eastern and western transects are 4.93 × 10-11 cm3 STP/g•year and 1.99 × 10-10 cm3 STP/g•year, respectively. These values reveal that the 4He accumulation rates may differ at least four times at different parts of a single aquifer, which are located 30 to 60 km apart. It is understood that any groundwater age-dating attempt by 4He requires a firm pre-assessment of spatial 4He accumulation rates. He isotope signal in the groundwater of KCB proves the mantle and/or crustal gas input into the carbonate aquifer in which an on-going hypogenic karst development has been suspected

Role of hypogenesis in the evolution of karst in the Taurus Mountains Range, Turkey

Field observations and laboratory data collected from the Taurus Mountains Range, Turkey during the last two decades provided evidence for the link between the evolution of hypogene karst and the geodynamic history. Major evidence includes; carbonate-hosted secondary ore deposits that are converted from primarily hypogene minerals by epigene, oxygen-rich groundwater circulating at local to intermediate depths. Another piece of evidence of hypogene karst in the Tauride is the Kırkgöz springs’ huge submerged cave/conduit system, which formed the Antalya Travertine Plateau, which is the world’s largest deposit precipitated by cool karst groundwater. The obruks in central Tauride are giant collapse dolines formed by ascending hypogene fluids in the upper continental crust, rich in volcanogenic carbondioxide. The groundwater’s noble gas and carbon isotope data are helpful in determining the existing but asymptomatic hypogene activity in the upper crust. Hypogene karst development seems common in parts of the world with current or past geodynamic activity. However, a hydrogeological overview of the geodynamic history is essential to assess the hypogene processes and their reflections on the land surface