Fossil diatom flora from the marine Paleogene stratigraphic key section of northeast Kamchatka, Russia

The Oligocene diatom flora from the marine Paleogene stratigraphic key section of northeast Kamchatka is described for the first time. The fossil flora contains a number of taxa of moderate to poor preservation and low abundance. Analysis of stratigraphic occurrence of diatoms throughout the section has been conducted. Two diatom assemblages of different ages are recognized in different parts of the 900 m-thick Alugivayam Formation. The younger assemblage is characterized by the presence of Cavitatus sp. cf. jouseanus and Odontella sawamurae. Co-occurrence of these taxamay indicate the age of enclosing sediment not older than ~31 Ma (the early Oligocene). The older assemblage from the basal part of the Alugivayam Formation lacks the mentioned taxa but contains Stephanopyxis species such as St. grunowii and St. marginata. Most likely, its age is at the earliest Oligocene. It is shown that in the studied Paleogene stratigraphic section diatoms appear just above the Eocene/Oligocene boundary. Data obtained on diatoms and diatom biomarkers may indicate increased diatom productivity in the sea basin after the Eocene/ Oligocene transition. The first data on diatom flora from stratigraphically well-controlled samples support the Oligocene age of the Alugivayam Formation in the Il’pinskii Peninsula section and contribute to regional correlations of theOligocene strata in Kamchatka