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 t hat precedes, but ends approximately 100 kyr before, the Frasnian-Famennian (F-F, mid-late Devonian) boundary mass extinction horizon. This horizon co rresponds to the final and most severe step of a more protracted extinction period. These results are inconsistent with data reported by others from t he upper Kellwasser horizon in Europe, which show anoxia persisting up to t he F-F boundary in most sections. Conditions returned to fully oxygenated p rior to the F-F boundary in the study area. These data indicate that the wo rst part of the F-F extinction was not related directly to oceanic anoxia i n this region and potentially globally. (C) 1999 Elsevier Science B.V. All rights reserved.