Early Middle Triassic (Anisian) trace fossils, ichnofabrics, and substrate types from the southeastern Germanic Basin (Wellenkalk facies) of Upper Silesia, southern Poland: Implications for biotic recovery following the Permian/Triassic mass extinction

The late Olenekian to early Ladinian marine carbonates of the epicontinental European (Germanic) Basin accumulated during the several-million-year-long biotic recovery following the Permian/Triassic (P/Tr) mass extinction. In this paper, we discuss the environmental and evolutionary controls on the temporal ichnodiversity and ichnofabric changes within Anisian open-marine limestones (called Muschelkalk) deposited in the south-eastern margin of the basin, close to the Tethys Ocean, and their implications for the timing of biotic recovery. The focus is on the lithologically similar transgressive systems tracts (TST) of three consecutive 3rd-order depositional sequences, each of which start with high-energy shoal-sand packstones-grainstones overlain by deeper-platform lime mudstones with skeletal and conglomeratic tempestites. In general, these facies are characterized by a high degree of bioturbation, high ichnotaxonomical diversity (20 softground ichnotaxa, 2 firmground ichnotaxa, 3 hardground ichnotaxa, and undetermined mottles and spots in a soupground suite), and high ethological diversity (domichnia, fodinichnia, cubichnia, repichnia, pascichnia, praedichnia). Despite the high overall diversity, monoichnospecific and almost monoichnospecific assemblages of Rhizocorallium, Oravaichnium, and Thalassinoides prevail. With these assemblages dominance changes stratigraphically, from Rhizocorallium dominated assemblages in TST1, to Oravaichnium dominated in TST2, and Thalassinoides dominated in TST3. Concurrently, the width of Thalassinoides burrows increases, from 1 to 2 cm in TST1 and TST2, to 3–7 cm in the TST3. The two secular changes may represent a gradual recovery of burrowing organisms following the P/Tr biotic crisis, given that environmental conditions remained more-or-less stable through time, as evidenced by facies analysis and stable carbon and oxygen isotope data. The occurrence of large Rhizocorallium and medium-sized Thalassinoides represents the penultimate stage in recovery, whereas the widespread appearance of large Thalassinoides – comparable in size with typical pre-extinction Permian forms – marks the final recovery of trace-maker communities.