LATE PERMIAN CONODONT FAUNAL CHANGES SIGNIFY RAPID OCEANIC WARMING IN NORTHWEST PANGEA

Conodont microfossils have been central to unravelling the timing of the Permian – Triassic boundary interval because, unlike most other marine clades, they do not display major faunal turnovers at or preceding the boundary. This faunal stability is not present in northern high-latitudes, where whole-scale, generic-level replacement of conodont faunas occurred in the Late Changhsingian. This replacement parallels an abrupt depositional change from chert to shale. Widespread marine deposition of chert in northwest Pangea -the Permian Chert Event beginning in the Lower Permian and persisting into the Late Permian- has been attributed to climatic cooling and an associated transition from carbonate- to silica-factory shelf sedimentation. Conodonts recovered from Late Permian chert deposited in northwest Pangea belong to a long-ranging low diversity Mesogondolella ex. gr. M. rosenkrantzi fauna that is recognizable from East Greenland to northwestern U.S.A., but is absent in coeval Tethyan strata. No elements of the M. rosenkrantzi fauna are present in the suprajacent shale; instead conodont faunas consist of the typical Tethyan forms Clarkina spp. and Hindeodus spp. for which there are no evolutionary precursors in northwestern Pangea. We interpret this faunal replacement as extinction of cool-water adapted forms and subsequent establishment of warm-water adapted forms. Ocean circulation models that appeal to stagnation and stratification of oceans and greenhouse related warming of oceans at this time uphold this interpretation.