Details

Autor(en) / Beteiligte

• Bond, D.P.G

Titel

Oceanographic changes during the Frasnian-Famennian mass extinction

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

2004

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• The extinctions at the Frasnian-Famennian (F-F, Late Devonian) boundary constitute one of the "big five" crises of the fossil record, and as many as 80% of the world's marine species became extinct. The extinction affected both benthic and pelagic groups, and appears to have been particularly severe for tropical to subtropical species. Several causal mechanisms have been proposed, including extraterrestrial impact, sea-level fluctuations, and global climate change. The extinction interval is associated with two organic-rich limestones, the "Kellwasser" beds, in condensed, deep-water German boundary sections: consequently, marine anoxia has also been proposed as a cause of the mass extinction. Evidence for these anoxic events has been sought in palaeogeographically widespread sections, in Germany, France, Poland, the Great Basin of the western United States, and New York State, using integrated techniques of pyrite framboid assay, traditional facies analysis, and gamma-ray spectrometry. New data from sections representing a variety of depositional settings, suggests that the main anoxic pulse, widely known a the "Upper Kellwasser Event", occurred during the topmost Frasnian, throughout Europe and North America, and was intensive and extensive, and, crucially globally synchronous. This event was manifest as an expansion of the oxygen minimum zone, which resulted in the spread of anoxic waters from epicontinental basins into the upper water column, and into previously oxygenated shelf and shallow-water environments. The tiny, enigmatic tentaculitoids were amongst the principle causalities of the extinction. Despite often reaching rock-forming densities before their demise at the Frasnian-Famennian boundary, they have previously received little attention, and are the subject of a detailed study here. The intervention and inclusion of anoxia into previously oxygenated environments during the latest Frasnian is perfectly coeval with the tentaculitoid extinction as well as that amongst other groups, and global anoxia is therefore considered to have been a main cause of the Frasnian-Famennian mass extinction.