Bioherms of the Bozhekhan uplift in the Cis-Baikal trough as a marginal barrier reef system of a Cambrian salt basin of the southern Siberian platform

Modern forecast, exploration and development of hydrocarbon deposits within natural carbonate reservoirs of buried bioherm (reef) structures in the north of the Irkutsk region and the Sakha Republic (Yakutia) areas within the NepaBotuoba Anticline apply the most advanced technologies of 3D seismic exploration and geoelectric prospecting supplemented with a set of new interpretation approaches and analysis attributes contrasted against wide range of well logging data. The recent discoveries of hydrocarbon deposits in the northern reefs shoved the bioherms of the Irkutsk amphitheater in the shadow. The purpose of this research is geological study of biohermal carbonate formations of the Lower Cambrian age in the outcrops of the Bozhekhansky megaswell in the Baikal region. The choice of this object of study is due to the fact that the first oil and gas inflows were obtained from the wells of the Atovskaya, Osinskaya, Birkinskaya, Khristoforovskaya, Balykhtinskaya and Tuturskaya areas. Field geological routes and office processing of data on cuts and polished thin sections of sample surfaces were carried out including microscopic studies in the thin sections of samples and archival collections of cores from deep oil and gas prospecting wells. In 2021–2022, while prospecting in the south of the Irkutsk amphitheater, the authors explored stratified, nodular and columnar stromatolites found within the compound Bozhekhan megaswell of Cambrian carbonate outcroppings. Carbonate intraformational sedimentary breccias identified in the area under investigation feature a great variety in their fragment sizes and inclusions. The stromatolites’ structural features were studied by the cuts and polished thin sections of sample surfaces. Microphytolites were found in the thin sections and described. The authors also took advantage of the opportunity to study an archive collection of the thin sections of VendCambrian and Lower Cambrian carbonate strata from the Akhinskaya area’s wells at the Bozhekhan megaswell and from the Upper-Lena uplift to the north-west. The conducted study implies that Cambrian bioherm outcroppings of the Bozhekhan megaswell-type uplift within the Cis-Baikal trough are, in a sense, model geologic objects. The study of biologic and genetic varieties of Lower Cambrian phytolites, diagnostic features of the organogenic structures, their inner structure and formation processes of the reef ecosystem may provide a region-level prognostic key to the research of Cambrian sediment system in the south of the Siberian platform.

1. Obruchev V. A. Geology of Siberia: monograph. In 3 vol. Moscow – Leningrad: Academy of Sciences of the USSR; 1935–1938. 1357 p. (In Russ.).

2. Mel'nikov N. V. Vendian-Cambrian saline basin of the Siberian platform: stratigraphy and development history. Novosibirsk: Siberian Research Institute of Geology, Geophysics and Mineral Resources; 2018. 177 p. (In Russ.).

3. Varlamov A. I., Efimov A. S., Kontorovich A. E., Kontorovich V. A., Korovnikov I. V., Pegel' T. V., et al. Stratigraphy of oil and gaz basins of Siberia. Cambrian of Siberian platform. Vol. 1. Stratigraphy. Novosibirsk: Trofimuk Institute of Petroleum Geology and Geophysics of the Siberian Branch of the Russian Academy of Sciences; 2016. 497 p. (In Russ.).

4. Dol'nik T. A. Stromatolites and microphytoliths in the stratigraphy of the Riphean and Vendian folded framing of the Siberian Platform. Novosibirsk: Geo; 2000. 317 p. (In Russ.).

5. Zharkov M. A., Chechel' E. I. Cambrian sedimentary formations of the Angara-Lena depression. In 3 parts. Part 1. General characteristics of the Cambrian deposits and the carbonate formation of the Angara-Lena depression. Novosibirsk: Nauka; 1973. 238 p. (In Russ.).

6. Korolyuk I. K. Comparative characteristics of the Riphean and Cambrian formations of the Baikal region. Moscow: Academy of Sciences of the USSR; 1962. 129 p. (In Russ.).

7. Stanevich A. M., Kornilova T. A., Mazukabzov A. M., Vahromeev A. G. Correlation and microfossils of VendCambrian sediments from Chaika parametrical borehole 279. Izvestiya irkutskogo gosudarstvennogo universiteta. Seriya “Nauki o Zemle” = Bulletin of Irkutsk State University. Series “Earth Sciences”. 2015;12:124-135. (In Russ.).

8. Migursky A. V., Staroseltsev V. S., Melnikov N. V., Ryabkova L. V., Sobolev P. N., Surnin A. I., et al. Experience of the Chaikinskoye uplift study – the major object of petroleum exploration on the Siberian platform. Geologiya i mineral'no-syr'evye resursy Sibiri = Geology and Mineral Resources of Siberia. 2010;4:14-25. (In Russ.).

9. Gaiduk A. V., Almendinger O. A. Formation conditions and criteria for prediction of areas of improved reservoir properties ancient Vendian-Cambrian reservoirs (for example, Danilovskiy license area (East Siberia)). Nauchno-tekhnicheskii vestnik OAO “NK ‘Rosneft'’”. 2013; 1:10-13. (In Russ.).

10. Kontorovich A. E., Varlamov A. I., Efimov A. S., Kontorovich V. A., Korovnikov I. V., Krinin V. A., et al. Stratigraphic scheme of Cambrian deposits, south of the cis-Yenisei area of West Siberia. Geologiya i geofizika. 2021;62(3):443-465. https://doi.org/10.15372/GiG2020206.

11. Kravchenko A. A., Pashevin A. M., Lavrenteva A. E. Oil-and-gas potential of the reef deposits in the Vilyuy syneclise south. Nauki o Zemle i nedropol'zovanie = Earth sciences and subsoil use. 2020;43(2):209-219. (In Russ.). https://doi.org/10.21285/2686-9993-2020-43-2-209-219.

12. Maksimova E. N., Chertina K. N. Cyclic structure of the Osinsky horizon on the example of a deposit of the Nepa-Botuoba anteclise. In: Litologiya osadochnykh kompleksov Evrazii i shel'fovykh oblastei: materialy IX Vseros. litologich. soveshch. (s mezhdunar. uch.) = Lithology of sedimentary complexes of Eurasia and shelf regions: materials of the 9th All-Russian lithological meeting (with international participation). Kazan; 2019, p. 271–272. (In Russ.).

13. Sukhov S. S. On the role of facies-sedimentological criteria in reconstruction of Cambrian paleobasins in the east of the Siberian Platform. In: Sovremennye problemy sedi-mentologii v neftegazovom inzhiniringe: trudy III Vseros. nauch. prakt. sedimentologich. soveshch. = Modern problems of sedimentology in oil and gas engineering: proceedings of the 3d All-Russian scientific and practical sedimentological meeting. 10–12 April 2017, Tomsk. Tomsk: Center for Training and Retraining of Oil and Gas Specialists; 2017, p. 209–214. (In Russ.).

14. Sukhov S. S., Fomin A. M., Moiseev S. A. Paleogeography as investigation tool of Cambrian reefs in the eastern part of the North-Tungusk petroleum area. Neftegazovaya geologiya. Teoriya i praktika. 2018;13(3). (In Russ.). https://doi.org/10.17353/2070-5379/28_2018.

15. Vakhromeev A. G., Smirnov A. S., Mazukabzov A. M., Gorlov I. V., Misyurkeeva N. V., Shutov G. Ya., et al. The upper Lena arched uplift is the main object of preparing a resource base of hydrocarbons in the south of the Siberian platform. Geologiya i mineral'no-syr'evye resursy Sibiri = Geology and Mineral Resources of Siberia. 2019;3:38-56. (In Russ.). https://doi.org/10.20403/20780575-2019-3-38-56.

16. Shutov G. Ya. The Upper Lena arched uplift as a new promising object for gas prospecting in the AngaraLena oil and gas-bearing area. Geologiya nefti i gaza. 1987;1:5-9. (In Russ.).

17. Vakhromeev A. G., Sverkunov S. A., Ivanishin V. M., Smirnov A. S., Gorlov I. V. Bioherm structures with cavern-connected pore space and abnormally high formation pressure of fluid systems in Vendian-Cambrian natural carbonate reservoirs in the south of the Siberian Platform. In: Stroenie litosfery i geodinamika: materialy XXVII Vseros. molodezhn. konf. = Lithospheric structure and geodynamics: materials of the 27th All-Russian youth conference. 22–28 May 2017, Irkutsk. Irkutsk: Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences; 2017, p. 54–56. (In Russ.).

18. Smirnov A. S., Vakhromeev A. G., Kurchikov A. R., Gorlov I. V., Kokarev P. N., Kasyanov V. V., et al. Identification and mapping of fluid-saturated anisotropic cavern cracked collectors of the Kovyktinsky gas-condensate deposit. Geologiya, geofizika i razrabotka neftyanykh i gazovykh mestorozhdenii = Geology, geophysics and development of oil and gas fields. 2019;5:4-12. (In Russ.). https://doi.org/10.30713/2413-5011-2019-5(329)-4-12.

19. Korolyuk I. K. Structural features of swells in the southern part of the Baikal region on the example of the Bozhekhan uplift. In: Tektonika neftegazonosnykh oblastei Sibiri = Tectonics of the oil and gas regions of Siberia. Moscow: Nauka; 1967, p. 60–70. (In Russ.).

20. Zamaraev S. M. Marginal structures of the southern part of the Siberian platform. Moscow: Nauka; 1967. 248 p. (In Russ.).

21. Zamaraev S. M., Adamenko O. M., Ryazanov G. V., Kul'chitskii A. A., Adamenko R. S., Vikent'eva N. M. Structure and development history of the Cis-Baikal piedmont depression. Moscow: Nauka; 1976. 134 p. (In Russ.).

22. Vasil'ev V. G., Ivanova M. N., Mordovskii V. T. On the inter-area of the East Siberian and West Siberian platforms in terms of oil and gas potential assessment. In: Voprosy neftegazonosnosti Sibiri = Issues of oil and gas potential in Siberia. Moscow: Gostoptekhizdat; 1959, p. 69– 75. (In Russ.).

23. Zharkov M. A., Zamaraev S. M. The history of tectonic development of the south of the Siberian platform. In: Voprosy sravnitel'noi tektoniki drevnikh platform: materialy soveshch. po problemam tektoniki = Issues of comparative tectonics of ancient platforms: proceedings of the conference on tectonic problems.1–7 February 1963, Moscow. Moscow: Nauka; 1964, p. 135–145. (In Russ.).

24. Mazur V. B. Structure of the eastern part of the Irkutsk amphitheater and tectonic features of the deposits of the Lena stage. In: Geologiya i neftegazonosnost' yuga Vostochnoi Sibiri = Geology and oil and gas potential of the south of Eastern Siberia. Moscow: Nedra; 1969, p. 148– 154. (In Russ.).

25. Trufanova N. V., Krivoshchekov A. L., Naumova Yu. A. Methodology and results of kinematic interpretation for the regional profile “Kovykta field – Predpatomsky trough”. Tekhnologii seismorazvedki. 2007;3:83-91. (In Russ.).

26. Karasev I. P. Lithological-stratigraphic and geochemical characteristics of the rocks in the south of the Siberian platform. In: Geologiya i neftegazonosnost' Vostochnoi Sibiri = Geology and oil and gas potential of Eastern Siberia. Moscow: Gostoptekhizdat; 1959, р. 8–186. (In Russ.).

27. Kononov A. I. New data on the tectonics of the southeastern part of the Siberian Platform. Geologiya i neftegazonosnost' Vostochnoi Sibiri = Geology and oil and gas potential of Eastern Siberia. Moscow: Gostoptekhizdat; 1959, р. 356–434. (In Russ.).

28. Odintsov M. M., Pavlovskii E. V. History of geological study. In: Geologiya SSSR. T. XVII. Irkutskaya oblast'. Ch. 1. Geologicheskoe opisanie = USSR Geology. Vol. 17. Irkutsk region. Part 1. Geological description. Moscow: Nedra; 1962, p. 9–15. (In Russ.).

29. Pritula Yu. A., Efremov M. I., Bazanov E. A., Mandel'baum M. M., Savinskii K. A., Karasev I. P., et al. Results of exploration works for oil and gas in the Irkutsk region and a plan of regional works for the period from 1965 to 1970. In: Geologiya i neftegazonosnost' yuga Sibirskoi platform = Geology and oil and gas potential of the south of the Siberian platform. Iss. 247. Leningrad: Gostoptekhizdat; 1966, p. 151–159. (In Russ.).

30. Adamov E. A., Tsobin V. A., Chechel' E. I. Some features of the geological structure and development of the Ilga depression in terms of potential potassium content. In: Trudy Instituta geologii i geofiziki = Proceedings of the Institute of Geology and Geophysics. Iss. 116. Novosibirsk: Geo; 1970, p. 100–110. (In Russ.).

31. Korolyuk I. K. Some Cambrian stromatolites of the Irkutsk amphitheater. In: Trudy Instituta nefti = Proceedings of the Institute of Oil. Iss. 7. Alma-Ata: Academy of Sciences of the Kazakh SSR; 1956, p. 51–59. (In Russ.).

32. Korolyuk I. K. Comparative characteristics of the Riphean and Cambrian formations of the Baikal region. Moscow: Academy of Sciences of the USSR; 1962. 129 p. (In Russ.).

33. Britan I. V., Zharkov M. A., Kavitskii M. L., Kolosov A. S., Mashovich Ya. G., Chechel' E. I. Structure and formation conditions of the Cambrian salt-bearing deposits on the territory of the USSR. In: Problemy solenakopleniya = Problems of salt accumulation. Vol. 2. Novosibirsk: Nauka; 1977, р. 203–227. (In Russ.).

34. Chechel' E. I., Mashovich Ya. G., Gilev Yu. G. Structural regularities of Cambrian salt-bearing deposits in the south of the Siberian Platform. Moscow: Nedra; 1977. 144 p. (In Russ.).

35. Kalinkina L. I., Shutov G. Ya. Reef deposits of the Middle Mot subformation of the Nepa arch in the south of the Siberian platform. Sovetskaya geologiya. 1981;1:6872. (In Russ.).

36. Myshevskii N. V. The Ignyalinsky barrier reef as a new promising object on the Nepa arch. Geologiya i geofizika. 1991;32(11):99-107. (In Russ.).

37. Bagrintseva K. I. Formation conditions and properties of oil and gas carbonate reservoirs. Moscow: Russian State University for Geological Prospecting; 1999. 285 p. (In Russ.).

38. Dol'nik T. A., Vorontsova G. A. Biostratigraphy of the upper Precambrian and lower Cambrian horizons of the North Baikal and Patom highlands (based on the study of stromatolites and microphytoliths). Irkutsk: Vost.-Sib. kn. izd-vo; 1974. 95 p. (In Russ.).

39. Zhuravleva I. T. Early Cambrian orogenic structures on the territory of the Siberian Platform. In: Organizm i sreda v geologicheskom proshlom = Organism and environment in the geological past. Moscow: Nauka; 1966, p. 61–84. (In Russ.).

40. Maslov V. P. On the Conophyton stromatolite nature. Problemy paleontologii = Problems of Paleontology. Vol. 4. Moscow: Paleontological Laboratory of the Moscow State University of the USSR; 1938, p. 325–332. (In Russ.).

41. Maslov V. P. Principles of stromatolite nomenclature and classification. Izvestiya Akademii nauk SSSR. Seriya geologicheskaya. 1953;4:105-112. (In Russ.).

42. Maslov V. P. Stromatolites and facies. Doklady Akademii nauk SSSR. 1959;125(5):1085-1088. (In Russ.).

43. Luchinina V. A. Paleoalgology under transition from cyanobacterial (stromatolitic) to algal ecosystem on the example of the Cambrian deposits of the Siberian Platform. In: Rifogennye formatsii i rify v evolyutsii biosfery = Reef formations and reefs in biosphere evolution. Moscow: Borissiak Paleontological Institute of the Russian Academy of Sciences; 2011, p. 26–37. (In Russ.).

44. Stanevich A. M., Nemerov V. K., Chatta E. N. Proterozoic microfossils of the Sayan-Baikal folded area: habitats, nature and classification. Novosibirsk: Geo; 2006. 200 p. (In Russ.).

45. Tepleev A. A., Luchinina V. A., Cocnovckaya O. V., Bagmet G. N. Calcareous algae and the lower boundary of Cambrian in the western part of the Altai-Sayan folded region. Geologiya i geofizika. 2004;45(4):485491. (In Russ.).

46. Kolosov P. N. Late Precambrian microorganisms of the east of the Siberian platform. Yakutsk: Yakut Branch of the Siberian Branch of the USSR Academy of Sciences; 1984. 84 p. (In Russ.).

47. Smetanin A. V. Experience of dynamic interpretation of gravitational anomalies. Irkutsk; 2000. 85 p. (In Russ.).

48. Gubina E. A., Tikhonova K. A., Vinokurova O. A., Lukyanov V. V., Volkov V. G., Neustroev K. A., et al. Model of the Osinsky productive horizon (formation B1) in the fields of the Irkutsk region. Neftyanoe khozyaistvo. 2022;2:46-51. (In Russ.). https://doi.org/10.24887/0028-2448-2022-2-46-51.

49. Vakhromeev A. G. Kornilova T. A., Misyurkeeva N. V., Stepanova N. I., Shemin G. G., Urenko R. A., et al. The Bozhekhan uplift of the Cis-Baikal depression as a marginal barrier-reef system of the Cambrian salt-bearing basin in the south of the Siberian Platform. In: Geodinamicheskaya evolyutsiya litosfery Tsentral'no-Aziatskogo podvizhnogo poyasa (ot okeana k kontinentu): materialy nauch. soveshch. = Geodynamic evolution of the Central Asian mobile belt lithosphere (from ocean to continent): materials of the scientific meeting. 19–22 October 2021, Irkutsk. Irkutsk: Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences; 2021, iss. 19, p. 24–26. (In Russ.).