Anoxia pre-dates Frasnian-Famennian boundary mass extinction horizon in the Great Basin, USA

Major and trace metal results from three Great Basin stratigraphic sections with strong conodont biostratigraphy identify a distinct anoxic interval that precedes, but ends approximately 100 kyr before, the Frasnian-Famennian (F-F, mid-late Devonian) boundary mass extinction horizon. This horizon corresponds to the final and most severe step of a more protracted extinction period. These results are inconsistent with data reported by others from the upper Kellwasser horizon in Europe, which show anoxia persisting up to the F-F boundary in most sections. Conditions returned to fully oxygenated prior to the F-F boundary in the study area. These data indicate that the worst part of the F-F extinction was not related directly to oceanic anoxia in this region and potentially globally. (C) 1999 Elsevier Science B.V. All rights reserved.