Famennian
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| Famennian | |
|---|---|
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| Name | Famennian |
| Time start | 372.2 |
| Time end | 358.9 |
| Time unit | Ma |
| Chronostrat | Upper Devonian |
Famennian
The Famennian is the uppermost stage of the Devonian Period, spanning from about 372.2 to 358.9 million years ago. It succeeds the Frasnian and precedes the Tournaisian of the Carboniferous, and it is defined by global stratigraphic markers used by the International Commission on Stratigraphy and recognized in regional scales such as the North American and European chronostratigraphies. The interval records major biotic crises, widespread reef decline, and important faunal turnovers that influenced later Paleozoic ecosystems.
Definition and Stratigraphic Position
The Famennian occupies the uppermost subdivision of the Devonian Series, equivalent to the late Devonian epoch in regional schemes such as the ICS timescale and the Geologic Time Scale. Its lower boundary follows the Frasnian–Famennian boundary defined by conodont biozones and chemostratigraphic markers used by the Subcommission on Devonian Stratigraphy and later ratified by the International Geoscience Programme. The stage is correlated with regional stages like the Kasimovian only in discussions of broader chronostratigraphy linking Paleozoic sequences to the Mississippian succession of Europe and North America. Key stratotypes lie in sections studied by geologists from institutions such as the University of Geneva and the British Geological Survey.
Chronology and GSSP
Absolute age estimates for the Famennian derive from radiometric dating methods applied to volcanic ash layers and diagenetic minerals analyzed by laboratories at organizations like the Geological Survey of Canada and the Swiss Seismological Service. The Global Boundary Stratotype Section and Point (GSSP) for the base of the Famennian was ratified using conodont markers in a reference section correlated with records from the Rhenish Massif, Belgium, and the Holy Cross Mountains samples analyzed by teams from the University of Warsaw and the Vrije Universiteit Brussel. Chronostratigraphic correlation employs chemostratigraphy (carbon isotope excursions) recognized by researchers at the Lamont–Doherty Earth Observatory and the Smithsonian Institution.
Paleogeography and Climate
Paleogeographic reconstructions for the Famennian show continental configurations assembled by plate motions modeled by groups at the Paleomap Project and the University of Chicago; major landmasses included Laurussia, Gondwana, Siberia, and microcontinents like Avalonia and Armorica. Paleoclimate evidence from isotopic studies by the University of Oxford and the Max Planck Institute for Chemistry indicates global cooling trends punctuated by transient warming events linked to shifts in ocean circulation recorded in cores from the Boreal Realm and the Rhenish Facies. Sea-level changes inferred by teams at the United States Geological Survey and the Nordic Geological Surveys document regressions and transgressions that reshaped shallow marine shelves around regions such as Laurentia and Baltica.
Biotic Events and Extinctions
The Famennian records the latter phase and aftermath of the Late Devonian mass extinction events, including the Hangenberg event as characterized by paleontologists affiliated with the Natural History Museum, London and the Panama Paleontology Research Group. Extinction impacts affected major taxa such as placoderms, trilobites, brachiopods, and reef-building stromatoporoids documented in museum collections at the Smithsonian Institution and the Muséum national d'Histoire naturelle. Recoveries and radiations in groups like actinopterygians, sarcopterygians, and early tetrapodomorphs were studied by teams from the University of Chicago and the Field Museum. Biotic turnover also influenced pelagic communities including ammonoids showcased in collections at the Natural History Museum of Paris and the Senckenberg Gesellschaft für Naturforschung.
Lithology and Depositional Environments
Famennian strata comprise carbonate platforms, black shales, marls, and siliciclastic wedges observed across exposures in the Rheinisches Schiefergebirge, Appalachians, Anti-Atlas, and Tasmania. Sedimentology studies by researchers at the University of Sydney and the University of Toronto show facies transitions from reefal carbonates dominated by stromatoporoid buildups to deeper-water anoxic black shale intervals akin to sequences in Kuwait and the North Sea Basin. Diagenetic and geochemical work conducted at the Geological Survey of Norway and the Bureau of Economic Geology uses biomarkers and trace element proxies to infer oxygenation events in basins like the Rhenish Basin and the Dniester Basin.
Major Fossil Assemblages
Fossil assemblages include diverse vertebrates, invertebrates, and plants curated at institutions such as the American Museum of Natural History and the Royal Ontario Museum. Notable occurrences include placoderm remains in the Old Red Sandstone exposures of Scotland, ammonoid faunas in the Caucasus and Morocco, conodont successions in the Holy Cross Mountains and Belgium, and plant macrofossils from Rhynie Chert-type floras and the Catskill Formation. Important taxa studies were produced by researchers affiliated with the University of Cambridge, University of Bonn, Yale University, University of California, Berkeley, and the Naturhistorisches Museum Wien.
Research History and Economic Significance
Historical investigations of the Famennian by figures associated with the Geological Society of London and the French Academy of Sciences advanced understanding of Late Devonian stratigraphy; key stratigraphers included workers from the University of Strasbourg and the Natural History Museum, Berlin. Economic interest centers on hydrocarbon source rocks and reservoirs in Famennian black shales and carbonates exploited in regions overseen by the Norwegian Petroleum Directorate and the Alberta Energy Regulator. Mineral deposits including phosphorite and metalliferous concentrations have been assessed by the US Geological Survey and the British Geological Survey for resource exploration. Ongoing multidisciplinary research continues at centers like the University of Leeds, University of Freiburg, Peking University, and the Australian National University.