FORAMINIFERAL BIOSTRATIGRAPHY ON OLIGOCENE OF WESTERN SIBERIA

Tavdinskaya suite and such name horizon including foraminiferal zone Cibicidoides pseudoungerianus, Evolutononion decoratum. This zone have been dated by author as middle Oligocene or Rupelian age. Bentic and planctic calcareous Foraminifera there are in this zone. Assemblage of planctic Foraminifera have included such characteristic spocies as Globigerina ampliapertura Bolli, G. officinalis Subbotina praesentata Podobina and others instead G. tapuriensis Blow et Banner and G. officinalis Subbotina which have been showed in Regional Stratygraphic Sheme 2001. The first species (G. tapuriensis) is characteristic for lower Oligocene (Latdorfian stage), the second one have known in upper Eocene of West Siberian and other regions. The Rupelian age of Tavdinskaya suite have based on findings of several characteristic Foraminifera which spreding onthis level in Europe, South-Eastern of USA and Atlantic ocean. In specimens from Boom formation (Stratotype of Rupelian in Belgium) the Foraminifera have been picked out by author. These Foraminifera are similar in systematic composition to West Siberian ones from Tavdinskaya suite. The boundary between Eocene and Oligocene (between Njurolskaya and Tavdinskaya suites) have been established on the base of different foraminiferal systematic composition and litology of these suites. Alsotectonic movements and paleogeographic events have been took into account on this boundary.<br /> In the sections of Southern Europe, Middle Asia, USA and Atlantic the lower Oligocene (or Latdorfian stage) and its foraminiferal planctic zone Globigerina tapuriensis have been established in these sections. The interruption in rock accommodation between these suites may be corresponded to Latdorfian age. On the base of factorial data Latdorfian stage must be restored as lower Oligocene. The Rupelian stage better return back on the former place (middle Oligocene).