Data on a series of boreholes drilled in the central trans-Urals are used to characterize the Paleocene marine deposits of the Talitsa Horizon, which are widespread all over the trans-Urals and in West Siberia. Presented paleogeographic considerations are based on distribution patterns of various fossils (foraminifers, radiolarians, dinocysts, and Selachii teeth) and on lithologic characteristics of their host deposits. Presented in addition are brief descriptions of underlying Maastrichtian (Gan'kino Formation) and overlying Thanetian (Serov Formation) deposits. The character and position of the Cretaceous-Paleogene boundary that is placed at the Talitsa Horizon base are described. Regional zonation of foraminifers and dinocysts is substantiated, and problems of regional and interregional correlations are briefly discussed.

The regional stratigraphic scheme suggested for the marine Paleogene deposits in the West Siberian plate is based on investigation results of macro- and microfossils (foraminifers, dinoflagellates, radiolarians, diatomaceous algae, silicoflagellates, Elasmobranchii, ostracodes, pollen, and spores). In the West Siberian plate, like in many structural-facies zones of the East European platform, there was a hiatus in sedimentation at the Cretaceous-Paleogene boundary. The Talitsa Horizon corresponds here to the Danian and Selandian presumably coupled with the initial Thanetian. The lower Lyulin-Vor Subhorizon is dated bask to the late Paleocene; the middle Lyulin-Vor Subhorizon is correlated with the Ypresian, and the upper one is attributed to the interval spanning the second half of the Ypresian and Lutetian, The Tavda Horizon of the Bartonian-Priabonian age presumably comprises as well the terminal Lutetian, The Kurgan Beds is. str,) representing marine facies of the Atlym Horizon correspond in the type area (near the town of Kurkan) to the lower Oligocene. Boundaries of these lithostratigraphic units are diachronous, since the Paleoarctis in the north and the Tethys in the south were connected with the epicontinental West Siberian sea basin producing an irregular impact on sedimentation in the latter.

Stratigraphic position and distribution of the lower Oligocene Kurgan Beds in southern West Siberia are considered. Their age is substantiated by the data on malacofauna, ichthyofauna, dinocysts, spores, and pollen. Two scenarios of their formation are probable. According to the first one, the Kurgan Beds were accumulated during the retreat of already brackish Tavda sea from the West Siberian plate in the Eocene-Oligocene boundary time. The second scenario, which seems more probable, especially for the southern areas of the West Siberian plate, supposes the repeated sea ingression from the western Turan plate via the Turgai depression in the early Oligocene (Ashcheairyk) time. Similarly to the sea expansion into the Middle Volga and Cis-Uralian areas along the older river system in the Akchagylian time (Pliocene), the Kurgan sea spread from the south to the north for more than 1000 km along the erosional Turgai depression and former Tobol valley with its tributaries, To the north and east of the town of Kurgan, seawaters penetrated into the Omsk syncline and negative landforms behind the Middle Urals. An extensive deposition of brown iron ores in the Turgai depression (the Lisakovsk basin with estimated reserves of two billion tons) is related to the Kurgan sea ingression. The iron ores were formed at the "geochemical barriers" in the mouths of rivers flowing into the sea strait. A high percentage of small pollen grains of Quercus graciformis and other thermophilic plants in the Kurgan Beds is likely a consequence of both the warm seawater ingression to the north and partial reworking of underlying Tavda sediments, where that pollen is dominant component of palynological spectra.