End-Permian mass extinction of lagenide foraminifers in the Southern Alps (Northern Italy)

The Permian-Triassic boundary, examined at two sections in the Southern Alps, occurs similar to 1.0 to 1.5 m above the base of the Tesero Oolite Member of the Werfen Formation in a depositionally continuous sequence of inner neritic carbonates. Lagenide foraminifers from the boundary interval comprise 27 species in 15 genera plus additional unidentified taxa, most of which became extinct during the end-Permian crisis. The only survivors were Nodosaria elabugae and unidentified species in Geillitzina and Nodosinelloides, with representatives of the latter two genera being short-term holdovers. The end-Permian lagenide extinction level occurs a few decimeters below the biostratigraphically defined erathem boundary, just above the contact between the Bulla Member of the Bellerophon Formation and the overlying Tesero Oolite Member. Confidence intervals (> 96%) for the lagenide extinction at the two sections are 0.03 and 0.04 to thick. Plots of species' stratigraphic abundance versus their last observed occurrences below the estimated extinction intervals at both localities are consistent with abrupt extinction or gradual extinction lasting no more than the time required for 1 m of rock to accumulate. Blooms of the foraminiferal disaster taxa Rectocornuspira kalhori and Earlandia sp. occur in the extinction interval and continue well into the Dienerian part of the Mazzin Member of the Werfen Formation, consistent with a protracted survival phase. A detailed carbon isotope record has been obtained from rocks bracketing the extinction at the well-known Tesero section. The combined microfossil and carbon isotope data indicate that the extinction occurred during an initial negative shift in delta C-13. Therefore, the negative excursion is likely to be related to the cause of extinction and unlikely to be merely a consequence of extinction.