Pre-Valanginian unconformity features in north-east parts of the Western Siberia

UDK: 551.763.1(571.1)

DOI: 10.24887/0028-2448-2025-5-79-83

Key words: Western Siberia, Lower Cretaceous, stratigraphic unconformity, key horizons

Authors: G.L. Rozbaeva (Tyumen Petroleum Research Center LLC, RF, Tyumen); S.E. Agalakov (Tyumen Petroleum Research Center LLC, RF, Tyumen); V.A. Marinov (Tyumen Petroleum Research Center LLC, RF, Tyumen); A.Yu. Kolmakov (Tomsk State University, RF, Tomsk)

The results of studies of a large stratigraphic unconformity at the base of Cretaceous deposits in the territories of Western Siberia are presented. Due to new data obtained during the work to estimate the oil and gas potential of the Cretaceous strata, the volume and area distribution of stratigraphic unconformity in the section of Cretaceous deposits in the interior of Western Siberia were pointed. The stratigraphic volume of sediments missing in the section as a result of their non-accumulation/erosion in the pre-Valanginian time was estimated. Based on new data on biostratigraphy, magnitostratigraphy, sedimentology, and the results of geophysical studies of wells, a partial or complete absence of Ryazan stage sediments in the territory of the Pur-Taz interfluve was established. A method for detecting signs of stratigraphic unconformity in deep layers of the Western Siberia sedimentary basin is proposed. It is established that the occurrence of the pre-Valanginian unconformity is associated with a regressive sequence of facies. The formation of the layer overlying the unconformity surface reflects the transgressive stage of sedimentation. The stratigraphic position of the formation bottom changes within the age interval of accumulation of the transgressive formation, which is recorded by stratigraphic methods. Since the age interval of forming of the transgressive formation is much smaller than the volume of stratigraphic unconformity, the surface can be considered as quasi-isochronous. In accordance with the requirements of the Stratigraphic Code of Russia, the presence of stratigraphic unconformity is proposed to be reflected in regional stratigraphic schemes.

References

1. Baraboshkin E.Yu., Veymarn A.B., Kopaevich L.F., Naydin D.P., Izuchenie stratigraficheskikh pereryvov pri proizvodstve geologicheskoy s"emki (Study of stratigraphic breaks during geological survey), Moscow: Publ. of MSU, 2002, 163 p.

2. Stratigraficheskiy kodeks Rossii (Stratigraphic Code of Russia), St. Petersburg, Publ. of Karpinsky Russian Geological Research Institute, 2019, 96 p.

3. Saks V.N., Ronkina Z.Z., Yurskie i melovye otlozheniya Ust'-Eniseyskoy vpadiny (Jurassic and Cretaceous deposits of the Ust-Yenisei depression), Proceedings of

Institute of Arctic Geology, 1957, V. 90, Leningrad: Gosgeoltekhizdat Publ., 1957, 232 p.

4. Marinov V.A., Zlobina O.N. et al., The biostratigraphy and sedimentary environments of the lower cretaceous section, Malaya Kheta structural-facies region, West Siberia (In Russ.), Geologiya i geofizika, 2015, V. 56, no. 10, pp. 1842–1853.

5. Kurkin A.A., Yankova N.V., Kuznetsov V.I., Stulikov S.K., Berriasian-Hauterivian shale sequence and associated pinch-out trap prospects of the Yamal peninsula

(In Russ.), Izvestiya vuzov. Neft' i gaz, 2018, no. 1, pp. 13–21.

6. Nezhdanov A.A., Kulagina S.F., Gerasimova E.V., The influence of late cimmerian folding upon stratification of early neocomian deposits in West Siberia (In Russ.),

Ekspozitsiya Neft' Gaz, 2017, no. 7(60), pp. 18–22.

7. Marinov V.A., Agalakov S.E., Dubrovina L.A. et al., Markiruyushchie gorizonty melovoy sistemy Zapadnoy Sibiri kak osnova regional'noy korrelyatsii (Marking horizons of the Cretaceous system of Western Siberia as a basis for regional correlation), Collected papers “Melovaya sistema Rossii i blizhnego zarubezh'ya: problemy stratigrafii i paleogeografii” (Cretaceous system of Russia and neighboring countries: problems of stratigraphy and paleogeography), Proceedings of XII All-Russian Conference, 7-11 October 2024, Yuzhno-Sakhalinsk: Indigo Publ., 2024, pp. 143–146.

8. Potapova A.S., Vilesov A.P., Chertina K.N. et al., Signs of the subaeral exposition at the border of Abalak and Tutlim (Bazhenov) suite (In Russ.), Geologiya, geofizika i razrabotka neftyanykh i gazovykh mestorozhdeniy, 2018, no. 11, pp. 13–19, DOI: https://doi.org/10.30713/2413-5011-2018-11-13-19

9. Lapina L.V., Lebedev M.V., Levkovich O.S. et al., The Yanovstan formation of Western Siberia: internal structure and results of zoning (In Russ.), Neftyanoe khozyaystvo = Oil Industry, 2024, no. 8, pp. 48–53, DOI: https://doi.org/10.24887/0028-2448-2024-8-48-53

10. Rozbaeva G.L., Agalakov S.E., Marinov V.A. et al., Results of stratigraphic breakdown of Lower Cretaceous deposits in Payakha oil and gas accumulation zone (West Siberian Yenisei-Khatanga petroleum region) (In Russ.), Geologiya nefti i gaza, 2025, no. 2, pp. 37–51, DOI: https://doi.org/10.47148/0016-7894-2025-2-57-71

11. Aleynikov A.N., Kutsman A.N., Biostratigrafiya nizhnekhetskoy svity Vankorskogo neftegazovogo mestorozhdeniya (Biostratigraphy of the Nizhnekhetskaya suite of the Vankor oil and gas field), Collected papers “Regional'naya geologiya. Stratigrafiya i paleontologiya fanerozoya Sibiri” (Regional geology. Stratigraphy and paleontology of the Phanerozoic of Siberia),. Novosibirsk: Publ. of SNIIGGiMS, 2009, pp. 130–141.

12. Marinov V.A., Kislukhin I.V., Merkulov V.P. et al., Kharakteristika pogranichnykh yursko-melovykh otlozheniy Bol'shekhetskoy strukturnoy terrasy (Zapadnaya Sibir') (Characteristics of the Jurassic-Cretaceous boundary deposits of the Bolshekhetskaya structural terrace (Western Siberia)), Collected papers “Melovaya sistema Rossii i blizhnego zarubezh'ya: problemy stratigrafii i paleogeografii” (Cretaceous system of Russia and neighboring countries: problems of stratigraphy and paleogeography), Proceedings of IX All-Russian Conference, Belgorod, 17-21 September 2018, Belgorod: POLITERRA Publ., 2018, pp. 178–182.