Abstract: Kızılcahamam Beşkonak region is situated in Northern Anatolia which is attributed to the southernmargin of European Continent. Geological history between Cretaceous and Pliocene is an alternation of volcanic andtectonic events. This instability gave little chances to installation and establishment of lacustrine sedimentary basins.In a relatively disactive short duration of the magmatie activity of "Galatian Andesite Massive" a lacustrine regime,in which different and rich variety fauna and flora developed, were placed in Beşkonak volcanic deppresion.Sedimentary facieses in one hand and intraformational structures (underwater slumps, pseudonodules and clasticdykes) in other hand are expressions of sedimentation in versant basins. All these parameters define volcano-biosedimentary system as environmental type.Subject of research based initialy to paleoecologic and paleogeographic analysis enlarged by comprehension ofdinamics of volcanism, a phenomenon accompanied, and analysis of pyroclastic products. Utilisation of results presentscertain contributions in the fields of stratigraphy and paleogeography as well as paloecology.