Zoophycos–Skolithos Ichnofabric in Viséan Deposits of the South Tatar Arch: Cross-Cutting Relationships and Evidence of Marine Influence

Bioturbated Viséan sandstone–siltstone intervals of the South Tatar Arch have been interpreted as recording short-lived marine influence, but their ichnological basis has not been examined in detail. This study assesses the palaeoecological significance of a Zoophycos–Skolithos ichnofabric from Well 22XX80. A core specimen from 1213.5 m, approximately 2 m above eroded Tournaisian limestones and beneath a 5.5-metre-thick sandstone body, was studied on a natural split surface and in oriented cuts; the associated trace-fossil assemblage and bioturbation intensity were also recorded. Two lamellar systems are preserved. System B is assigned to Zoophycos isp., whereas System A contains structures referred to as cf. Zoophycos and cf. Teichichnus. Subvertical Skolithos burrows cross-cut System B. The lamellae of the Zoophycos spreite terminate at the burrow walls and are absent from the fill, establishing their relative order of formation. The broader assemblage, including Planolites, Teichichnus, Helminthoida and indeterminate burrows, is compatible with Palaeozoic expressions commonly assigned to the Cruziana Ichnofacies. Together with the lithological succession and regional stratigraphic context, the ichnological evidence supports marine conditions in the lower bioturbated interval. The upward transition to the overlying sandstone may reflect higher hydrodynamic energy, although greater clastic supply or migration of the depositional zone remain alternative explanations. The study illustrates the value of cross-cutting ichnofabric relationships preserved in core for recognising short-lived marine influence in siliciclastic successions.