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R. Thomas Becker

Analysis of ammonoid palaeobiogeography in relation to the global Hangenberg (terminal Devonian) and Lower Alum Shale (Middle Tournaisian) events

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Abstract

The global ammonoid record of the latest Famennian (Wocklumian) to Upper Tournaisian is reviewed in order to analyze patterns of the palaeogeographical distribution, developments in time and to elucidate the influence of the international Hangenberg and Lower Alum Shale Events. Occurences of 77 genus-level taxa in 61 sedimentary provinces are summarized. The terminal Devonian Hangenberg Event caused a major ammonoid extinction but had little lasting influence on their palaeobiogeography. However, there was an unusual very short-timed spreading of ammonoid facies in formerly uninhabitated areas of North America, Europe and NE-Siberia. The Lower Alum Shale Event at the base of the classical Middle Tournaisian, by contrast, marks a major palaeobiogeographical turning point associated with a medium scale extinction. Centres of evolution shifted from the Europe-Ural area to the west (North American interior) and east (Kazakhstan) and globally there is no significant faunal sequence crossing the event level. Endemism and faunal dispersal continue in the Upper Tournaisian with some evidence for the separation of two faunal provinces. The increasing spread of goniatite biofacies (enlargement of species-areas) as sign of sealevel highstand and wide overflooding of epicratonic areas curiously is not paralleled by an increase of global diversity. This may reflect non-palaeogeographic factors such as global climatic change. In a taxonomic chapter potential subdivisions of the genera Acutimitoceras, Imitoceras and Eocanites are discussed. The Prodromitidae are assigned to the Prionocerataceae.

Pour citer cet article

R. Thomas Becker, «Analysis of ammonoid palaeobiogeography in relation to the global Hangenberg (terminal Devonian) and Lower Alum Shale (Middle Tournaisian) events», Annales de la Société géologique de Belgique [En ligne], Fascicule 2 - Devonian-Carboniferous boundary, Volume 115 (1992), 459-473 URL : https://popups.ulg.ac.be/0037-9395/index.php?id=3013.

A propos de : R. Thomas Becker

Paläontologisches Institut, Freie Universität Berlin, Schwendener Str. 8, 1000 Berlin 33, Deutschland.