2D–3D Expression of Planolites and Teichichnus in Two Viséan Core Specimens: Insights from X-Ray Micro-CT

Trace fossils in drill cores are observed as two-dimensional (2D) expressions whose morphology varies with section orientation, complicating ichnotaxonomic identification. We compared exposed and polished surfaces with X-ray micro-computed tomography (micro-CT) reconstructions of two intensely bioturbated Viséan core specimens from the Volga–Ural Petroleum Province. In the two specimens, tubular structures corresponding to Planolites were visible in both reconstructed volumes, whereas Teichichnus was clear on polished surfaces but its 3D expression varied. Small dark structures seen in 2D show a locally branching geometry in the reconstructed volume and are tentatively referred to as cf. Chondrites. Core logging in both wells records Zoophycos-bearing strata above the studied Planolites–Teichichnus intervals, in agreement with the regional increase in marine influence during the Viséan. High-resolution micro-CT of two ~1 mm3 ROIs at a voxel size of ~4 μm shows higher resolved porosity in the host matrix than in the sandy burrow fill.