Paleoenvironmental evolution of the late Pliocene-early Pleistocene fluvio-deltaic sequence of the Denizli Basin (SW Turkey)

•The Late Pliocene-Early Pleistocene Tosunlar succession reflects shallow-water delta.•The mollusc faunas and their stable isotopes show a (semi-) isolated brackish lake.•The Tosunlar endemic faunal composition remained constant throughout succession.

The late Pliocene-early Pleistocene Tosunlar succession (Denizli Basin, southwestern Turkey) represents fluvial-dominated delta environments at the margins of a brackish long-lived lake. Two main facies associations are documented: (i) a delta front facies association, with a distal (DF1) and proximal (DF2) deposits; and (ii) a delta plain facies association that contains distributary channel (DP1) and interdistributary swamp (DP2) deposits.The stable isotopic analysis of the mollusc faunas exhibit a narrow range of values (-4.68 < δ18O < + 0.21‰ and + 0.43 < δ13C < + 3.27‰, respectively) and the very poor δ18O-δ13C correlation (r = − 0.16) may indicate hydrologically open lake and significant diagenetic alteration. The mollusc faunas and their stable isotope ratios show a biogeographically isolated brackish lake system under semiarid climatic conditions. Under special environmental conditions the endemic faunal composition remained constant which is very unusual for a (semi-) isolated long-lived lake setting.