The Nevşehir-Acıgöl maar is one of the eruption centers of Quaternary volcanism in central Anatolia. The Maar-lake fill contains clastic, chemical and organic deposits, including high-calorific peats formed in the Late Holocene. The main (host) sediments of the infill are tuffaceous sandy mudstones. The other accessory facies, controlled mainly by climate, are peats and plant-bearing mudstones, brecciated mudstones, limestones and also travertines originated by thermal waters at the top of the succession. According to the C.14 dating of the peats, they formed ca. 2000 yrs BP; their calorific values are 2300 to 3165 kCal/kg. These values are very high, considering the immaturity of the peats. It is thought that the lake was primarily dependent on climate; and deposition was further controlled by the hydrothermal system. The associated heat flow played an important role in sedimentation by creating a micro-climatic niche, where late-Quaternary (cold regional climate) vegetation could flourish and form substantial peat deposits. The heat flow through the groundwater and clastic sediments must have been crucial during the high maturation of the peat deposits.