Copyright © 2015 by The Geochemical Society of Japan. ignimbrite eruption (11–2.8 Ma), and c) the formation of stratovolcanoes, such as Erciyes, Melendiz Dag, and Hasan Dag, as well as numerous small monogenetic centers that erupted during the late Pliocene until recent times (Piper et al., 2002). The CO2 produced from different geological units and reservoirs exhibits different chemical characteristics. Previously published water chemistry data are presented in Table 1. The Karbogaz Field (Aksaray) is located in the eastern corner of the Tuz Golu Basin. Two superimposed aquifers are located within the field: the lower confined (gypsum, siltstone, and sandstone) and the upper unconfined (alluvium). The lower confined aquifer contains a high amount of dissolved CO2 (20–30 mg/L) (Geosan, 1998). According to their chemical composition, the wellhead waters are defined as Na–Ca–HCO3–Cl-type waters (Table 1). The wellhead waters within the Bozkar Field are defined as Na–Cl-type waters and the amount of dissolved CO2 is 469.45 mg/L (Table 1). The Guneygaz–Kemerhisar Field, located to the south of the city Nigde, consists of two aquifers: tuffites and alluvium. The Kemerhisar region wellhead waters have a similar chemical composition to the Na–Cl-type water. While shallow reservoir water contains only small amounts of dissolved CO2 (2–21 mg/L), the water within the tuffite aquifer has a high concentration of CO2 (102.8–1,280.7 mg/L) (Table 1) (Geosan, 1998). In the Karapιnar Field (Konya Province), water samples indicate predominantly Na–Cl/Ca–Mg–HCO3-type waters. The amount of dissolved CO2 varies in the range from 395.11 to 1,041.24 mg/L (Table 1). Origin of carbon dioxide occurrences in Central Anatolia (Turkey)