Paleobotanical features of Tyumen and Naunak formations (middle-upper jurassic of the south-east of West Siberia)

The relevance. Traditional use of data of geophysical researches of wells for stratigraphic subdivision and correlation of stratigraphicunits of the South'East of Western Siberia is not always possible to confidently draw boundaries between lithological similar deposits. In this relation the difficulties in constructing geological models of fields occur, that can result in inefficient exploration and increase in cost of development of deposits of hydrocarbon raw materials. The aim of the research is to form complexes of plants typical for the Tyumen and Naunak formations for biostratigraphic subdivision and correlation of oil-productive deposits of the South-East of Western Siberia (areas Snezhnaya and Dvoinaya). Objects: paleobotanical remains from the core of boreholes in Snezhnaya and Dvoinaya areas, as well as the published material from previous studies. Methods. To determine the imprints of plants the authors have used the comparative morphological and epidermal-cuticular methods. Imprints of fossil plants were studied under binocular microscope MBS-1 and LOMO. For stratigraphic division and correlation of sediments the method of complex analysis of organic residues was applied. Results. The authors studied paleobotanical material from the middle-upper-Jurassic deposits of southeastern West Siberia (Snezhnaya and Dvoinaya) and determined distribution of plant taxa to certain strata (the Tyumen and Naunak). It was found out that ferns Coniopteris and Raphaelia diamensis vialovae and gymnosperms Czekanowskiales Phoenicopsis mogutchevae, Czekanowskia rigida and Cz. irkutensis are typical for the Tyumen formation. The endemic ferns Coniopteris latilobus and gymnosperms Czekanowskiales Czekanowskia tomskiensis and widespread coniferous Podozamites eichwaldii are typical for Naunak formation. Endemic structure of Naunak plant complex flora points to the specific conditions of Naunak strata formation. The stratigraphic units similar in lithological composition were separated. The authors developed the reliable base for stratigraphic division and correlation, which will be the base for construction of reliable geological model of deposits. This will result in more effective exploration in the South-East of Western Siberia.