The faunistic complex of the Domanik Formation of Southern Timan is characterized by primary development of the planctonic forms and almost complete absence of benthos, that makes it significantly different from the faunistic assemblages from the underlying and overlying deposits, being formed in depth similar conditions. Changes in structure of ostracods, ammonoids, conodonts and some other faunistic groups assemblages at the boundary of the Domanik and underlying Ust-Yarega Formations are considered. Critical factors in reorganization of faunistic assemblages are the changes in the basin bottom relief, such as topographical isolation of deep-water areas from the shallow-water sedimentation zone, formation of anoxic conditions at the depressions bottom and periodic inflow of silicic acid in the bottom water layers.