The End-Permian Mass Extinction

Ichnologic approaches have been key to the understanding of causes and consequences of the end-Permian mass extinction event ever since researchers began to focus on this pivotal episode in the history of life. Trace-fossil occurrences or absences have proven useful to recognize the loss in biodiversity and ecologic function during the extinction event as well as to track subsequent restoration of benthic marine communities. There exists now a considerable body of ichnologic data from many critical Permo-Triassic and especially Lower Triassic sections, which allows drawing a more advanced picture of the extinction event and subsequent recovery. The trace-fossil record of immediate post-extinction strata shows a virtual complete breakdown of bioturbation. First modest benthic activity is evidenced by the presence of simple deposit-feeding traces. Recent studies have advanced the notion that recovery, which is traditionally perceived to have proceeded slowly, was remarkably volatile with the reemerging of fairly complex and diverse ichnofaunas on a global scale soon after the extinction. Surveying the record of some key ichnotaxa, such as Arenicolites, Diplocraterion, Rhizocorallium, and Thalassinoides, also suggests that recovery was neither latitude-dependent nor did ichnotaxa reappear in a strict stepwise manner. It is more likely that the irregular recovery pattern of ichnofaunas results from a combination of a generally strong facies dependence of trace-fossils, a patchy geologic record, local environmental controls, and possibly a variable primary recovery signal. Recent work suggested that biogenic sediment mixing was strongly reduced during the aftermath of the end-Permian mass extinction. This must have had tremendous consequences for marine element recycling and burial, as well as ecosystem functioning. Based on observations from extant ecosystems, it can be hypothesized that Early Triassic sedimentary and geochemical signatures as well as ecologic intricacies mirror the depauperate ecology and low biodiversity left by the extinction. As examples, anoxic signatures, behavior of the sulfur-cycle, and paleoecologic characteristics are reevaluated in the light of the poor biogenic mixing scenario.