Double-trouble in the Devonian - extinction and anoxia
The extinctions at the Frasnian-Famennian (Late Devonian) boundary constitute one of the “big-five” crises of the Phanerozoic. Many faunal studies have been compiled, but these have never been properly integrated. A lack of high-resolution faunal range data has hindered our understanding of the extinction dynamics. Amalgamation of the faunal data available in the literature, at conodont-zone level, together with the author’s own findings from a variety of marine sections in Europe and the United States, has allowed recognition of the nature and timing of the extinction. In particular, the tentaculitoids, a group of small, conical animals which were locally abundant during the Frasnian, provide a detailed record of the extinction timing.A number of questions, crucial to our understanding of the extinction, will be explored: did the F–F extinction actually occur? If so, when, and how suddenly did it occur? How selective was the extinction? What was the significance of sea-level change during the extinction?There are a number of competing extinction mechanisms. The faunal range data has been correlated with the record of globally widespread anoxia, supported by a variety of geochemical and sedimentological techniques. This provides strong evidence of a causal link between marine anoxia and the extinction.