Distribution of foraminifera of the Gaudryinopsis Genus in the Jurassic-Paleogene of Western Siberia

The species of GaudryinopsisPodobina, 1975 Genus assigned previously to other genera have been met at different levels of the Jurassic-Cretaceous-Palaeogene. Thetests of species of the Gaudryinopsis Genus have a quartz-siliceous wall and a rounded cross-section. The representatives of the similarGaudryina Orbigny, 1840 Genus are characterized by a different chemical composition of the wall (the calcareous agglutinate with thesame cement) and by the angular cross-section of the test. The species of the Gaudryinopsis Genus have been considered from diversestratigraphic levels, and their development has been marked within the maximum transgressions in Western Siberia. That is why thespecies of the genus are often taken as zonal species. The Gaudryinopsis (Gaudryina) filiformis (Berthelin) Species is known establishedpreviously by G. Berthelin (1880) from the Albian of France. This species has first been discovered by us from the Middle Albiandeposits of the Polyarnaya-1 borehole section (depth 1748.34 m) in the Turukhansk district of the north-east Western Siberia. ItsTuronian descendants Gaudryinopsis angustus Podobina are relatively abundant in many borehole sections in the central district of thisregion, and their quantitative predominance is connected with the Early Turonian enlarged transgression. In the Santonian deposits ofWestern Siberia the Gaudryinopsis vulgaris (Kyprianova) Species is known. However, its finds are sparser in comparison with theTuronian species, and it is accordingly not accepted as a zonal species. In the Middle Eocene the most extensive transgression isobserved, and the Gaudryinopsis subbotinae Podobina Species has been confined to it and taken as zonal. The deposits of this zonecorrespond to the second middle Eocene rock complex from the Lomonosov Ridge section. This is evidenced by the lithology of theserocks composed of the bio-siliceous material, as the Lyulinvorskaya Suite is (the middle subsuite, the Gaudryinopsis subbotinae Zone).In the Lomonosov Ridge section, the underlying deposits of the lower Lyulinvorskaya Subsuite and the Talitskaya Suite correspond tothe similar dark-grey clays of the Palaeocene-lower Eocene of the third rock complex. The data on the lithology and stratigraphy havebeen taken from the paper of Akhmetyev, et al. (2010). The confinement of diverse species of the Gaudryinopsis Genus to depositscorresponding to the maximum transgressions enhances their stratigraphic and correlational significance for the refinement of the age ofthe most controversial stratums. So the wide lateral distribution and the narrow vertical occurrence of the Gaudryinopsis subbotinaePodobina Species in Western Siberia and of its middle Eocene vicariant Gaudryinopsis superturkestanika (Bykova) in Central Asia(Bykova, 1959) evidence the middle Eocene age of the Gaudryinopsis subbotinae Zone as well as that of the middle LyulinvorskayaSubsuite (Lyulinvorskaya Suite) to which this assemblage is confined.

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