First discovery of Mississippian trace fossils in the Świebodzice Unit from the Witoszów region (SW Poland)

Abstract

Abundant and moderately diverse trace fossil assemblage have been discovered for the first time in mudstones of the Pogorzała Formation from the Witoszów region, SW Poland. Fifteen ichnospecies including fourteen ichnogenera are described. The ichnofauna is dominated by Dictyodora liebeana and contains numerous Palaeophycus tubularis, rarer Archaeonassa fossulata, Archaeonassa isp., Chondrites cf. intricatus, Curvolithus simplex, Diplopodichnus biformis, Lockeia isp., ?Lophoctenium isp., Nereites isp., Phycosiphon isp., Protovirgularia isp., ?Psammichnites isp., Taenidium isp. and one ichnospecies of fish swimming trails, Undichna cf. britannica. Some other structures (wave ripples influenced by microbial mats and zigzag structures) also occur. The trace fossil assemblages differ in various exposures, but three of them are similar and display the Dictyodora liebeana ichnoassemblage. It is represented mostly by the ethological categories fodinichnia and repichnia, with fewer pascichnia, domichnia and cubichnia. This new data from the Świebodzice Unit sheds light on the palaeontology, age and paleoenvironment of the Pogorzała Formation. The occurrence of D. liebeana and U. cf. britannica indicates the Mississippian age of most mudstones studied, formerly considered Upper Devonian. The trace fossil assemblage belongs to the non-standard Nereites ichnofacies, without graphoglyptids. The lithological features of mudstones, trace fossil assemblage and poverty of macrofauna, testify to their deposition in a deeper sedimentation zone below storm wave base, most likely in dysaerobic, pro-delta conditions. This study suggests that rocks containing D. liebeana may form a correlative horizon in the Świebodzice Unit.