Abstract
The late Permian mass extinction event was the largest biotic crisis of the Phanerozoic and has the longest recovery interval of any extinction event. It has been hypothesised that subsequent carbon isotope perturbations during the Early Triassic are associated with biotic crises that impeded benthic recovery. We test this hypothesis by undertaking the highest-resolution study yet made of the rock and fossil records of the entire Werfen Formation, Italy. Here, we show that elevated extinction rates were recorded not only in the Dienerian, as previously recognised, but also around the Smithian/Spathian boundary. Functional richness increases across the Smithian/Spathian boundary associated with elevated origination rates in the lower Spathian. The taxonomic and functional composition of benthic faunas only recorded two significant changes: (1) reduced heterogeneity in the Dienerian, and (2) and a faunal turnover across the Smithian/Spathian boundary. The elevated extinctions and compositional shifts in the Dienerian and across the Smithian/Spathian boundary are associated with a negative and positive isotope excursion, respectively, which supports the hypothesis that subsequent biotic crises are associated with carbon isotope shifts. The Spathian fauna represents a more advanced ecological state, not recognised in the previous members of the Werfen Formation, with increased habitat differentiation, a shift in the dominant modes of life, appearance of stenohaline taxa and the occupation of the erect and infaunal tiers. In addition to subsequent biotic crises delaying the recovery, therefore, persistent environmental stress limited the ecological complexity of benthic recovery prior to the Spathian.
Highlights
The late Permian mass extinction event is the most catastrophic crisis to have affected life during the Phanerozoic, with a loss of an estimated 81% of marine species[1], and is associated with climate-induced environmental changes triggered by Siberian Traps volcanism[2,3]
Geochemical data shows that the Early Triassic is characterised by multiple carbon and oxygen isotope excursions with the late Griesbachian and Smithian/Spathian boundary (SSB) recording thermal maxima[8], which may have resulted in further environmental deterioration that delayed recovery from the extinction event[9]
We present the highest-resolution and most continuous quantitative dataset yet assembled from the entire Lower Triassic Werfen Formation, Italy, which allows a better control on the impact of faciesinduced bias on the interpretation of ecological changes
Summary
The late Permian mass extinction event is the most catastrophic crisis to have affected life during the Phanerozoic, with a loss of an estimated 81% of marine species[1], and is associated with climate-induced environmental changes triggered by Siberian Traps volcanism[2,3]. Subsequent crises delayed post-Permian benthic recovery i.e. first Triassic substage (e.g.[4,5]). Geochemical data shows that the Early Triassic is characterised by multiple carbon and oxygen isotope excursions with the late Griesbachian and Smithian/Spathian boundary (SSB) recording thermal maxima[8], which may have resulted in further environmental deterioration that delayed recovery from the extinction event[9]. Benthic biotic crises have been recorded at the Griesbachian/Dienerian boundary in Oman [5], and during the Dienerian in western US [10] and the Werfen Formation, Italy[11], but not at all locations [12]. A ‘brief reversal’ in regional recovery was recorded in the Smithian Campil Member of the Werfen Formation, northern Italy, but attributed to local facies change[11,15,16]. Evidence that the subsequent hyperthermals delayed the recovery of the benthos is, equivocal
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