Trace fossils and the aftermath of the Permo-Triassic mass extinction: evidence from northern Italy

Abstract

Abstract The duration of early Triassic anoxia in the carbonate ramp settings of the Werfen Formation (Dolomites, northern Italy) has been constrained using ichnofabric and sedimentological data. This includes fine lamination and abundant pyrite framboids commonly reworked into lags by storm events. The “anoxic” event spanned the entire Griesbachian Stage and extended from deep waters into extraordinarily shallow water settings; evidence for oxygen deficiency can be found in mid and inner ramp facies. The extent and duration of this event may at least partially explain the magnitude of the Permo-Triassic mass extinction. Normal benthic conditions returned rapidly in the Dienerian Stage and pervasively bioturbated distal ramp facies testify to the ventilation of the deeper water areas of the region in post-Griesbachian times. A post-mass extinction radiation is not particularly well displayed in either trace fossil or body fossil diversity compilations from the Dolomites. Moderate/low levels of trace fossil diversity are maintained throughout the post-Griesbachian Werfen Formation whilst the body fossil data shows a moderate increase from the mid-Smithian Stage. There is thus a curious lag period spanning the Dienerian to mid-Smithian when environmental conditions were apparently normal but the marine fauna failed to show any recovery.