Neoichnology of vertebrate traces along the western barrier coast of Ukraine: preservation potential and subsurface visualization

Abstract

A diverse quite of vertebrate traces covers beach, aeolian, and bay-side (deflation flats) surfaces along the NW Black Sea coast of Ukraine. These include avian, ungulate, and canid footprints, as well as mammal burrows (length >5 cm; depth ~2 cm). The preservation of biogenic structures is enhanced by rapid burial (low-energy sedimentation or event deposition), algal mat formation, and salt encrustation. Continuous high-frequency (800 MHz) ground-penetrating radar (GPR) imaging aided in visualizing subsurface sections of an active burrow complex within a beach-dune ridge. Images near an active fox burrow captured distinct subsurface anomalies (point-source hyperbolic diffractions) in the upper aeolian section above the water table. Unfilled tunnel sections are easily distinguished from buried roots and other targets based on signal velocity and polarity reversals relative to air-to-sediment response at the ground surface. The diffraction geometry (angle) is related to signal velocity, providing valuable information about relative saturation of the overlying substrate. Decimeter-scale deformation of shallow reflections may be attributed to tracking surfaces, with similar examples found immediately below modern surfaces affected by anthropogenic trampling. It is likely that muddy lagoonal tracking surfaces may be preserved under layers of sand (overwash or aeolian deposition) and, following saltwater expulsion, may be recognized in geophysical images as clear deformed paleo-surfaces. Heavy-mineral concentrations (e.g. magnetite-rich sand) are common for beach and dune horizons that have undergone reworking and such anomalies often accentuate physical and biogenic deformation structures. Due to moderate-to-high fraction of ferri- and paramagnetic minerals, these anomalies are also well-expressed in GPR images due to its electromagnetic signal response. A conceptual framework of trace preservation potential (taphonomy) and geophysical recognition (GPR) suitability is proposed for this coastal region, with implications to paleo-environmental reconstruction.