MATGROUND OASIS FACILITATING RAPID BIOTIC RECOVERY FOLLOWING THE END-PERMIAN EXTINCTION IN MARINE HABITABLE ZONE

Marine ecosystems experienced the most profound recovery following the Permian‒Triassic (P‒Tr) mass extinction during their Phanerozoic evolutionary history. Biotic recovery, however, occasionally occurred fast in some cases. For instance, trace-making organisms may recover faster in shallow marine habitable zone than in other settings, and also rebound faster in relatively higher latitudes than in low latitudes. Here, we present a new case that trace-makers recovered rapidly following the P‒Tr biocrisis in matground oasis of shallow marine habitable zone based on an anomalously diverse and high-tiering trace-fossil assemblage from the lowest Triassic sandstones in the southern Qilian basin of Qinghai Province, western China. The studied area was situated at the northern margins of the Paleotethys Ocean and located at moderate-high latitudes during the P‒Tr transition. The lowest Triassic sandstones yield abundant cross-beddings, ripple marks and microbially induced sedimentary structures (MISSs) as well as the Claraia-dominated bivalve assemblage of early-middle Griesbachian age, suggesting the relatively high-energy, fair-weather wave action zone in siliciclastic shallow sea. This lowest Triassic ichnoassemblage comprises 17 ichnospecies in 12 ichnogenera and is dominated by Diplocraterion with common presence of Rhizocorallium, Arenicolites, Bifungites, Rosselia, and Skolithos, all of which possess very high complexity and tiering levels, and usually mark ecologic recovery following major biocrises. Such a diverse ichnoassemblage therefore indicates that final stage of post-extinction recovery was much more rapid in the southern Qilian than most areas elsewhere in which biotic recovery usually occurred in Spathian.