A gap in sedimentation in the Silurian section of the Subpolar Urals at the Ludlow-Pridoli boundary

Research subject. The article discusses the results of a new detailed study of a reference section of the Upper Silurian in the Subpolar Urals. This study was undertaken to clarify the existing contradictions concerning the age of the Ludlow-Pridoli boundary deposits and the definition of the Ludlow-Pridoli boundary, which is based on the study of different fauna groups.

Materials and methods. The newly collected collections contained more than 100 samples of sedimentary rocks with fossil macro fauna, 22 tests on microfauna, 198 tests on chemical analysis for determining the content of Ba, Sr and δ13C and δ18O isotopes in carbonates. The results of experiments were confirmed by the authors’ bio-sedimentological, paleo-ecological and chemostratigraphic data.

Results. The conducted research confirmed the existence of a gap in sedimentation at the end of Ludlow; clarified the thickness of the Sizim stage in the reference section; elucidated its sedimentological and chemostratigraphic characteristics; allowed changes in biodiversity due to a change in the sedimentation regime, paleoecological impact on biota in the late Ludlow and restoration of biota in the early Pridoli to be traced. The study also demonstrated that the time boundaries of the transgressive and regressive stages in the development of the Northern Ural sea basin and the event-stratigraphic boundary of the Ludlow-Pridoli were directly related to the main global events in the Late Silurian (Lau Event, Lower Pridolian Event), the traces of which are preserved in the studied section.

Conclusions. The intensification of regressive tendencies across the largest part of the Northern Ural paleobasin in the Late Ludlow, widespread development of microbial biota, cessation of the Silurian reef formation, as well as the extinction of Pentamerida brachiopods – exclusively, indicate a significant ecosystematic restructuring in the late Ludlow. It can be assumed that the absence of a significant positive deviation of the δ13C global Lau Event in this section is associated with the identified gap, the amplitude of which correlates with the Ozarkodina snajdri and Ozarkodina crispa zones located above the Polygnathoides siluricus zone in the conodont sequence of the Upper Ludlow.

1. Abushik A.F. (2000) Silurian – earliest Devonian ostracode biostratigraphy of the Timan-Northern Ural region. Proc. Estonian Acad. Sci. Geol., 49(2), 112-125.

2. Antoshkina A.I. (2012) The Late Ludfordian anoxic Event from the Subpolar Urals. Vestn. IG Komi NTs UrO RAN, (2), 3. (In Russian)

3. Antoshkina A.I. (2018) The Ludfordian Lau Event (Upper Silurian) in the Northeastern Regions of European Russia. Stratigr. Geol. Korrel., 26(6), 15-40. (In Russian)

4. Baraboshkin E.Yu., Veirman A.B., Koraevich L.F., Naidin D.P. (2002) Izuchenie stratigraficheskikh pereryvov pri proizvodstve geologicheskoi s”emki [Study of stratigraphic breaks in the production of geological surveys].Moscow, Moscow St. Univ. Publ., 135 p. (In Russian)

5. Baranov V.V. (2015) Global events (Lower Pridolsky and Klonk) in the Middle Paleozoic in the northeast of Eurasia and in adjacent territories. Nauka i Obrazovanie, 79(3), 33-37. (In Russian)

6. Baranov V.V., Blodgett R.B. (2013) Correlation of the Pridolian beds (upper Silurian) of the Arctic regions of Eurasia and North America. Otech. Geologiya, 5, 52-57. (In Russian)

7. Beznosova T.M. (2008) Soobshchestva brakhiopod i biostratigrafiya verkhnego ordovika, silura i nizhnego devona severo-vostochnoi okrainy paleokontinenta Baltiya [Brachiopod communities and biostratigraphy of Upper Ordovician, Silurian and Lower Devonian of North-Eastern margin of Baltia paleocontinent]. Ekaterinburg, UrO RAN Publ., 218 p. (In Russian)

8. Beznosova T.M., Matveev V.A., Sokolova L.V. (2018) Biostratigraphical and event-stratigraphical boundary of the Ludlow and Pridoli on the Western slope of Subpolar Urals. Vestn. IG Komi NTs UrO RAN, (11), 31-37. (In Russian)

9. Beznosova T.M., Matveev V.A., Sokolova L.V. (2019) Upper Ludlowian-lower Pridolian stratigraphy, carbon isotope of the Timan-Northern Urals region. Építőanyag, (71)1, 24-37.

10. Beznosova T.M., Matveev V.A., Sokolova L.V., Kanev B.I. (2017) Regional traces of the global Ludfordian Event (Lau Event) from the outcrop of the Western slope of the Subpolar Urals. Geodinamika, veshchestvo, rudogenez Vostochno-Evropeiskoi platformy i ee skladchatogo obramleniya. Mat-ly Vseross. nauch. konf. s mezhdunar. uchastiem [Geodinamics, substance, ore genesis of the East European Platform and its folder framing: Extended of scientific conference reports]. Syktyvkar, IG Komi NTs UrO RAN, 19-21. (In Russian)

11. Calner M. (2005) Silurian carbonate platforms and extinction events – ecosystem changes exemplified from Gotland, Sweden. Facies, 51, 584-591.

12. Calner M., Jeppsson L., Munnecke A. (2004) The Silurian of Gotland. Part I: Review of the stratigraphic framework, event stratigraphy, and stable carbon and oxygen isotope development. Erlanger Geologische Abhandlungen. Sonderband, 5, 113-131.

13. Cherkesova S.V. (1970) Silurian Greben’ stage of the island Vaigach. Stratigrafiya i fauna siluriyskikh otlozhenii Vaygacha [Stratigraphy and fauna of Silurian deposits of Vaigach]. Proc. of the Scientific Research Institute of Geology of the Arctic. Leningrad, Trudy NIIGA, 4-24. (In Russian)

14. Isaev G.D. (2007) Korally, biostratigrafiya i geologicheskie modeli paleozoya Zapadnoi Sibiri [Corals, Biostratigraphy, and geological models of the Paleozoic strata of West Siberia]. Novosibirsk, Geo Publ., 247 р. (In Russian)

15. Jeppsson L. (1998) Silurian oceanic events. A summary of general characteristics. (Ed. M.E. Johnson). Silurian Cycles: Linkages of Dynamic Stratigraphy with Atmospheric, Oceanic and Tectonic Changes, James Hall Centennial Volume New York State Museum Bulletin, 491, 239-257.

16. Jeppsson L., Aldridge R.J. (2000) Ludlow (late Silurian) oceanic episodes and events. J. Geol. Soc., 157, 1137-1148.

17. Jeppsson L., Viira V., Männik P. (1994) Silurian conodontbased correlations between Gotland (Sweden) and Saaremaa (Estonia). Geol. Mag., 131(2), 201-218.

18. Kranz J.R. (1973) Die Strontium-Verteilung in den Arlbergschichten (Oberes Ladin) des Klostertales (Vorarlberg). Nördliche Kalkalpen. Neues Jahrb. Geol. Palaeontol., Monatsh, 170-187.

19. Krasnov V.I. (2011) The concept of the development of the organic world and the improvement of the stratigraphic basis of geological research. (On the example of the early Devonian of Salair. LVII Session PO, 70-72. (In Russian)

20. Kuznetsov V.G., Piip N.B. (1974) Strontium in Tournaisian deposits of the Orenburg region. Geokhimiya, (4), 585-593. (In Russian)

21. Kul’kov N.P. (1990) Brachiopods and their ecological assemblages. Silur i devon Yugo-Vostoka Zapadno-Sibirskoi plity. Skvazhiny Maizasskaya-1 i Maloichskaya-7. [Silurian and Devonian of South-eastern West-Siberian Plate. Borehole Maizasskaya-1 and Maloichskaya-7].(Eds N.P. Kulkov, N.V. Dubatolov). Moscow, Nauka Publ., 35-50. (In Russian)

22. Kul’kov N.P., Peregoedov L.G. (1990) Brachiopoda type. Stratigrafiya paleozoiskikh otlozhenii yugo-vostoka Zapadno-Sibirskoi plity [Stratigraphy of Paleozoic deposits in the southeast of the West Siberian plate]. Novosibirsk, Nauka Publ., 70-106. (In Russian)

23. Männik P. (2014) The Silurian System in Estonia. 4th Annual Meeting of IGCP 591, Abstracts and Field Guide (Eds H. Bauert, O. Hints, T. Meidla, P. Männik). Estonia, University of Tartu, 123-128.

24. Martynov A.V. (1998) Litologo-fatsial’nye kriterii prognoza neftegazonosnosti ordoviksko-nizhnedevonskikh otlozhenii Timano-Pechorskoi provintsii. Diss. … kand. geol.- min. nauk [Lithological and facies criteria for prognosis the oil and gas content of the Ordovician-Lower Devonian deposits of the Timan-Pechora province. Cand. geol. and min. sci. diss.]. St.Petersburg, 29 p. (In Russian)

25. Matveev V.A., Kanev, B.I. (2016) Features of the upper Ludlow deposits in the Silurian key section on the western slope of the Subpolar Urals. Vestn. IG Komi NTs UrO RAN, 8, 3-8. (In Russian)

26. Mel’nikov S.V. (1999) Konodonty ordovika i silura TimanoSeveroural’srogo regiona [Ordovician and Silurian conodonts of the Timan-Sever Ural region]. St.Petersburg, VSEGEI Publ., 136 p. (In Russian)

27. Modzalevskaya T.L. (1985) Brakhiopody silura i rannego devona evropeiskoi chasti SSSR. Otryad Athyridida [Silurian and the Early Devonian brachiopods from the European part of the USSR. Order Athyridida]. Moscow, Nauka Publ., 128 p. (In Russian)

28. Modzalevskaya T.L. (1997) Middle Ludfordian event in evolution of Silurian brachiopods of the European province. Stratigr. Geol. Korrel., 5(3), 3-9. (In Russian)

29. Modzalevskaya T.L., Marss T. (1991) On the age of the lower boundary of the Greben’ Regional Stage of the Urals. Izv. AN Estonii. Geol., (40)3, 100-103. (In Russian)

30. Modzalevskaya T.L., Wenzel B. (1999) Biostratigraphy and geochemistry of Upper Silurian brachiopods from the Timan-Pechora region (Russia). Acta Geol., 40(20), 145- 157.

31. Nekhorosheva L.V., Patrunov D.K. (1981) Greben’ stage of the Island Vaygach-Novaya Zemlya region. Sov. Geologiya, 4, 80-85. (In Russian)

32. Nikiforova O.I. (1970) Brachiopods of Greiben’ stage of the island Vaigach (Late Silurian). Stratigrafiya i fauna siluriiskikh otlozhenii Vaigacha [Stratigraphy and fauna of Silurian deposits of Vaigach]. Leningrad, 97-149. (In Russian)

33. Ob”yasnitel’naya zapiska k stratigraficheskim skhemam Urala (dokembrii, paleozoi) [Explanatory note to Ural stratigraphic maps Precambrian, Paleozoic]. (1994) (Ed. N.Ya. Antsygin). Ekaterinburg, Ural’skaya Geologos”emochnaya Ekspeditsiya Publ., 95 p. (In Russian)

34. Opornye razrezy pogranichnykh otlozhenii silura i devona Pripolyarnogo Urala [Reference sections of the Silurian/ Devonian Boundary Deposits of Subpolar Urals]. (1983) (Eds V.S. Tsyganko, V.A. Chermnykh). Syktyvkar, Komi filial AN SSSR Publ., 136 p. (In Russian)

35. Patrunov D.K., Shurygina M.V. (2002) Silurian and Early Devonian deposites of the Ufa Amphitheater. Litosfera, (2), 96-111. (In Russian)

36. Postanovleniya Mezhvedomstvennogo stratigraficheskogo komiteta i ego postoyannykh komissii [Resolutions of the Interagency Stratigraphic Committee and its standing commissions]. (2013) St.Petersburg, Publishing house VSEGEI. V. 42, 65 p. (In Russian)

37. Puchkov V.N. (1979) Batial’nye kompleksy passivnykh okrain geosinlklenal’nykh oblastei [Batial complexes of passive margins of geosynclinal regions]. Moscow, Nauka Publ., 242 p. (In Russian)

38. Smith R.E., Johnson J.G. (1977) Atrypella scheii (Holtedahl) and Atrypella phoca (Salter) (Silurian Brachiopoda). J. Paleontol., 51, 350-356.

39. Talent J.A., Mawson R., Andrew A.S., Hamilton P.J., Whitford D.J. (1993) Middle Palaeozoic extinction events: faunal and isotopic data. Palaeoecol., Palaeoclimat., Palaeogeogr., 104, 139-152.

40. Viira V., Aldridge R.J. (1998) Upper Wenlock to Lower Pridoli (Silurian) conodont biostratigraphy of Saaremaa, Estonia, and a correlation with Britain. J. Micropalaeontol., 17, 33-50.

41. Yudovich Yа.E. (1976a) Vvedenie v geokhimicheskuyu diagnostiku fatsii [Introduction to the geochemical diagnosis of facies]. Syktyvkar, IG Komi FAN SSSR, 116 p. (In Russian)

42. Yudovich Ya.E. (1976б) The nature of strontium anomalies in the Paleozoic strata of the Pechora Urals. Ezhegodnik-1975. Syktyvkar, IG Komi FAN SSSR, 107-112. (In Russian)

43. Yudovich Ya.E., Maidl’ T.V., Ivanova T.I. (1980) Geokhimiya strontsiya v karbonatnykh otlozheniyakh [Strontium Geochemistry of Carbonate Deposits]. Leningrad, Nauka Publ., 152 p. (In Russian)

44. Zhemchugova V.A., Mel’nikov S.V., Danilov V.N. (2001) Nizhnii paleozoi Pechorskogo neftegazonosnogo basseina: stroenie, usloviya obrazovaniya [Lower Paleozoic of the Pechora oil basin: structure and conditions of formation]. Moscow, Academy of Mining Sciences, 109 p. (In Russian)