New Campanian-Maastrichtian polymorphinids species (foraminifera) of Western Siberia

The paper outlines further results of the investigation on the Family Polymorphinidae from the material obtained from the boreholes of the south-eastern district of Western Siberia and also basing on the collections deposited in the Laboratory of Micropaleontology of TSU. This material enabled a number of new taxa (species and subspecies) of this family to be established. The descriptions of the Polymorphinidae taxa made by the author were based on five criteria (morphological, geochronological, paleogeographic, paleobiogeographic and the criterion of discreteness) proposed by A.V. Fursenko [1]. Two species and 5 subspecies are described from the deposits of the Gankinskaya Suite. The porosity character of the studied polymorphinid tests may be subdivided into two types. The first type is the most widespread; this is the porous surface of the test penetrated by the smallest spot holes 0.3-0.5 pm in size. The form of the holes is almost rounded; it is quite constant; pores are located unevenly or chain-like. Pores are simple: they are not limbate and are characteristic for numerous species assigned to the Genera Glandulina, Eoguttulina, Pyrulina, Sigmomorphina, Guttulina, Globulina, Ramulina. The taxa having the pores of the second type were not encountered. For establishing the specific and subspecific categories, the morphological, geochronological and paleogeographic criteria were mainly applied. The author revealed an obvious discrepancy with Kuzina [2] in determining the age of these species. So, with regard to the above-stated criteria, it became possible to distinguish new taxa in the Family Polymorphinidae. In describing species and subspecies, their alternative geographic and stratigraphic positions were established, which differ from those established previously. The wall porosity in established species and subspecies was analyzed by the electronic microscopy in the Institute of Biology and Biophysics of Tomsk State University. The description of foraminifera was performed according to the instruction on the systematic description of organisms developed in PIN RAS [3]. The factors of the habitat and geographic isolation play a significant role in the systematics of Polymorphinidae. This naturally suggests that the paleogeographic criterion must be taken into account. In studying new species and subspecies of the stated family, the discrepancy with Kuzina's data was revealed not only in age determination but also in the paleogeographic occurrence and location of polymorphinids. By Kuzina's information, the Guttulina ipatovcevi Vassilenko Species occurs only in the Upper Cretaceous of the Dnieper-Donetsk depression of Eastern Ukraine (the Romny District). The Siberian geographical subspecies Guttulina ipatovcevi Vassilenko sibirica Kseneva is common in the Campanian-Maastrichtian deposits of Western Siberia. All specimens of species described in the present paper are deposited in the Micropaleontological Department of the Paleontological Museum of Tomsk State University.

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