This study investigates the depositional environment of fluvial-lacustrine deposits in the Late Miocene-Pliocene-aged volcano-sedimentary deposits located between Başköy, Güzelöz, and Bayramhacılı (Kayseri), and Şahinefendi and Sofular (Nevşehir). The samples, which are representative of the deposits, were analysed to their mineralogical characteristics by polarized-light microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and geochemical and stable carbon and oxygen isotope analyses. The oxygen and carbon stable isotope values of carbonates indicate their formation under the influence of meteoric water that is related to the Messinian drought climatic conditions and the Mio-Pliocene global vegetation change.