Palaeoenvironments and faunal recovery after the end-Permian mass extinction

Abstract

Strata of the Lower Triassic Werfen Formation (Dolomites, northern Italy) record deposition in a Wide range of palaeoenvironments from peritidal to outer ramp settings. This enables accurate assessment of faunal recovery following the end-Permian mass extinction by eliminating facies-related effects. Extinction of the shelly taxa appears to be rapid and occurs in the latest Permian Tesero Oolite Horizon. Disappearance of the various trace fossil taxa appears to be more gradual. Following the extinction, the lower and middle Griesbachian are characterised by laminated sediments containing low diversity bedding plane assemblages. Ichnological, geochemical and sedimentological data show evidence of widespread low oxygen conditions. Normally oxygenated waters return in the late Griesbachian and there is a moderate increase in tiering above and below the surface. Macrofaunal and ichnofossil diversity decrease markedly during the Smithian, with the appearance of more terrigenous strata possibly reflecting an increased run-off and more brackish conditions. Complete recovery begins in the basal Spathian with an increase in tiering above and below the substrate. Crinoids and ammonoids appeal, for the first time in the Werfen Formation, and the ichnogenus Rhizocorallium re-appears. Global correlation is hindered by poor biostratigraphy in the Dolomites region. However, on a broad scale it appears as though many of the palaeoenvironmental changes are repeated worldwide. Current available data suggest that the re-appearance of some trace fossil taxa (e.g. Diplocraterion, Rhizocorallium) may be globally Synchronous.