The Callovian-Oxfordian deposits of the Pur-Irtysh, Taz-Kheta, and Sil’ga facies districts of West Siberia are considered, with emphasis placed upon their structure and composition as well as conditions of formation. In the first of them, the Callovian-Oxfordian deposits include the Vasyugan and Abalak Formations; in the second, the Tochino and Sigov Formations; and in the third, the Naunak Formation. Lithological and mineralogo-petrographical studies invoking well logging, geochemistry, and paleontology showed a difference of the Vasyugan Formation in the southeastern areas of the West Siberian Plate, in the mid-Ob’ region, and the Nadym-Taz interfluve. Thus, three facies subdistricts are recognized: Ob’-Tara, Ob’-Agan, and Nadym-Pur. In addition, the Yamal-Nadym facies subdistrict, where the Abalak Formation occurs, has been recognized.

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