The variations of terrestrial trace fossils and sedimentary substrates after the end-Permian extinction in the Dengfeng area, North China

Evolution of terrestrial infauna in the Early Triassic enables to understand terrestrial biotic recovery after the end-Permian mass extinction (EPME). Six ichnospecies in two ichnogenera, including Skolithos linearis, S. verticalis, S. annulatus, S. isp., Planolites montanus, and P. beverleyensis, were recognized from the Lower Triassic Liujiagou Formation (Induan Stage) and Heshanggou Formation (Olenekian Stage) in the Baiping section of the Dengfeng area, North China. The ichno-ecological analyses of ichno-taxonomic abundance, ichnodiversity, bioturbation index, burrow size, and tiering level revealed that terrestrial infauna expanded from epibenthic to endobenthic through the Early Triassic. The tiering deepening suggested that tracemakers gradually began to excavate into the sediments instead of moving on the microbial mats, indicating that the burrowing capability of trace-making animals has recovered in the Olenekian. Four types of sedimentary substrates were summarized: non-bioturbated matground, matground with bioturbated patches, weakly bioturbated mixed ground, and moderately bioturbated mixed ground. Occurrence of the substrate of mixed ground may be a sign of the initial recovery of the terrestrial ecosystem after the EPME.