Geologicheskii Vestnik

A comparison of a number of geochemical characteristics of mudstones, siltstones, very fine- and very fine-fine-grained sandstones (contents of SiO₂, Al₂O₃, K₂O and REE, values of Th/Sc, Th/Co, La/Sc, Cr/Zr, (La/Yb)_N and Eu/Eu*), allowing one to judge the composition of the parent rocks of the material composing them. The study is based on analytical data for 50 samples obtained during the study of clastic rocks of different grain sizes from productive formations YuV₄, YuV₃, YuV₂ and YuV₂⁰ of the North-Pokachevskoye oil field (Shirotnoye Priobye). It is shown that in the example we studied, the bulk chemical composition of both the mudstones themselves, siltstones, and very fine- and very fine-fine-grained sandstones is quite close, according to a number of criteria, to the gross chemical composition of clayey rocks. This gives reason to think that the role of clay minerals in the composition of the studied rocks, which differ in granulometric composition, is very high. Features of the localization of individual and average data points of the rock classes of different granulometry on discriminant diagrams, traditionally used to establish the composition of source rocks of aluminosiliciclastics, allow us to conclude that the results obtained from geochemical studies of a wide range of fine-grained clastic rocks (from mudstones to very fine-fine-grained sandstones) fairly comparable.

North-Pokachevskoye oil field, Shirotnoye Priobye, clastic rocks of different grain size classes, comparison of geochemical characteristics

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