Using Ichnofossils to Correlate Oil-Bearing Deposits in the Devonian Clastic Succession (Pashyian and Timanian Horizons) of the South Tatar Arch

Abstract

This article outlines the results of the first-ever ichnological study of the Middle Devonian clastic succession in the South Tatar Arch. The analysis of the stratigraphic distribution of trace fossils in the boreholes revealed several levels with biogenic structures such as ichnofossils and bioturbation, which proved useful for the correlation of the boreholes. The boundary interval of the Pashyian and Timanian Horizons is made up by a succession of three layers: bioturbated siltstones with Spirophyton burrows, limestones, and mudstones with Lingulichnus burrows. The interval can be traced over the entire area of the South Tatar Arch and may serve as an additional marker for the boundary between the horizons.

From Clastics to Carbonates and Black Shales: Deciphering Sedimentary Continuity and Discontinuity in the Devonian Landscape of the Volga-Ural Petroleum Province

“…Finds of soft tissues of lingulids favour dysaerobic conditions. Lingulid burrows of reduced length (5-10 mm instead of 50-70 mm) were also found here (Miftakhutdinova, 2023), indicating that the primary sediment was compacted.…”

“…In the works of many researchers, the origin of clastic sediments was associated with continental alluvial processes (Danilova, 2008;Loscheva et al, 2017). Meanwhile, recent studies (Silantiev et al, 2022, Miftakhutdinova, 2023 have confirmed the marine origin of these sediments and linked them to transgressive episodes of the Devonian marine basin.…”

“…We adhere to the viewpoint (Silantiev et al, 2022;Miftakhutdinova, 2023) that clayey-siltstone beds were formed in the conditions of the Cruziana Ichnofacies, localised between the levels of weak and storm waves. Sandy packs could have been formed in the Skolithos Ichnofacies, represented, most often, by well-sorted sands that had been constantly moved and subjected to sudden erosion or redeposition (Mikulash and Dronov, 2006;Bromley, 1996).…”

“…The total thickness of the core intervals studied exceeds 600 metres. Some of the findings, particularly on the clastic interval of the Givetian, which include detailed well logs, rock descriptions, and ichnofossil illustrations have been published recently (Silantiev et al, 2022;Miftakhutdinova, 2023). In-depth analysis of the well cores was conducted directly at the core storage facility, where highly representative rock samples were selected for closer examination.…”

“…The thicknesses range from the first hundreds of metres in depressions (and basinal low-plains) to the first tens of metres in uplifted areas of the seabed (including tectonic arches) representing shallow water environments. Marine fossils are rare; meanwhile, a diverse assemblage of ichnofossils including Chondrites, Spirophyton, Scolicia, Planolites, Palaeophycus, Zoophycos and Skolithos indicates the marine origin of these sediments (Silantiev et al, 2022, Miftakhutdinova, 2023. The Paschyian Regional Stage represents the time during which clastic sedimentation completely covered the entire studied area, displacing all other types of sedimentation.…”