Frasnian-Famennian extinction

Frasnian-Famennian extinction
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Name	Frasnian-Famennian extinction
Time period	Late Devonian
Ca	~372–359 million years ago
Severity	Major mass extinction
Affected	Marine taxa, reef ecosystems, vertebrates, plants
Possible causes	Anoxia, sea-level change, volcanism, bolide impact, climate change

Frasnian-Famennian extinction The Frasnian-Famennian extinction was a major Late Devonian biotic crisis that drastically reduced global biodiversity and reshaped Paleozoic ecosystems. Occurring near the boundary between the Frasnian and Famennian stages, this event involved abrupt collapses of reef communities, extensive losses among marine invertebrates, and selective extirpations that influenced the later evolution of tetrapods and fishes. Scientific investigation spans stratigraphy, paleontology, geochemistry, and paleoclimatology, engaging researchers from institutions and projects worldwide.

Background and Geological Setting

The Late Devonian coincided with tectonic and paleogeographic reorganizations that involved the assembly of Pangea, interactions among Laurentia, Baltica, Siberia, and Gondwana, and the development of extensive continental shelves. Sedimentary basins such as the Catskill Formation, Old Red Sandstone, Kaskaskia Sequence, and deposits in the Murgab Depression record transgressive–regressive cycles linked to eustatic shifts described by studies from the International Commission on Stratigraphy, Geological Society of America, and regional surveys. Reef systems dominated by stromatoporoids and rugose corals colonized shallow shelves across the Rheic Ocean margins and Iapetus Ocean remnants, with major carbonate platforms documented in the Holy Cross Mountains, Anti-Atlas, Canning Basin, and Appalachian Basin. Concomitant orogenic events including the Acadian orogeny and pulses in the Variscan orogeny influenced sediment flux and basin subsidence recorded by teams at the United States Geological Survey and the British Geological Survey.

Extinction Event and Timing

Biostratigraphic markers such as conodont zonation, ammonoid turnovers, and brachiopod assemblages constrain the crisis to a relatively brief interval near the Famennian onset, with multiple extinction pulses recognized in sections from the Kellwasser Horizon equivalents, Famennian Stage beds, and Devonian successions studied by the International Union of Geological Sciences. High-resolution chemostratigraphy, magnetostratigraphy, and radiometric calibration from laboratories at the Max Planck Society, Smithsonian Institution, and Geological Survey of Canada reveal at least two main pulses—commonly termed the Lower and Upper Kellwasser events—followed by a protracted ecological decline. Correlative sections in the Rheinisches Schiefergebirge, Rhenish Massif, Anticosti Island, and Moravia demonstrate synchronicity across paleocontinents, though regional diachroneity and hiatuses complicate precise temporal correlation pursued by researchers at the University of Oxford and Utrecht University.

Causes and Mechanisms

Hypotheses for causal mechanisms combine evidence for widespread marine anoxia, eustatic sea-level fall and rise, greenhouse and ice-house climate oscillations, large-scale volcanism, and possible extraterrestrial impacts. Geochemical signals interpreted as euxinia and anoxia arise from sulphur and iron cycling studies by groups at the Earth Observatory of Singapore, analyses linked to the Kellwasser Event context, and isotope work undertaken at the California Institute of Technology. Large igneous province activity such as the emplacement of the Viluy Traps has been proposed by researchers at the Russian Academy of Sciences and the Institute of Geology and Mineralogy (Novosibirsk), while impact scenarios invoke ejecta horizons compared across multiple cores examined by teams at the University of Cincinnati and the Royal Ontario Museum. Terrestrial drivers include the expansion of early forests dominated by progymnosperms and lycopsids, studied by paleobotanists at the Natural History Museum, London, which may have altered weathering rates, nutrient flux, and atmospheric composition in modeling performed at the University of Leeds and Princeton University.

Biological Impact and Taxonomic Losses

Marine reef-builders such as stromatoporoids and rugose corals experienced near-global collapse, a pattern documented in paleobiological surveys by the Paleobiology Database and researchers at the Smithsonian Institution National Museum of Natural History. Pelagic and benthic invertebrates including many brachiopod genera, trilobites in regional provinces like the Armorican Massif, and numerous reef-associated gastropods and bivalves declined sharply in datasets curated by the Natural History Museum, Paris and the Royal Belgian Institute of Natural Sciences. Conodont faunas show major turnover used for biostratigraphy by the International Commission on Stratigraphy, while placoderm and sarcopterygian lineages were differentially affected according to studies from the American Museum of Natural History and University of California, Berkeley. Survivorship was selective: nektonic ammonoids diversified subsequently, and early tetrapodomorph fishes that contributed to tetrapod origins persisted in refugia examined by teams at the University of Cambridge and Yale University.

Environmental and Geochemical Evidence

Isotope excursions in carbon (δ13C), oxygen (δ18O), and sulfur (δ34S) measured in cores from Anticosti Island, the Kellwasser Formation, and the Rhenish Slate Mountains indicate perturbations to the carbon cycle and episodes of global cooling and warming analyzed by groups at the University of Geneva and ETH Zurich. Black shale horizons enriched in organic carbon and molybdenum, and pyrite framboid distributions reported by researchers at the University of Texas at Austin and Woods Hole Oceanographic Institution support widespread anoxia and euxinia. Palynological records from the Rhynie chert–adjacent basins and continental sequences cataloged by the Natural History Museum, London reveal terrestrial vegetation shifts and soil erosion signals consistent with enhanced nutrient delivery, a linkage explored in geochemical models by the Massachusetts Institute of Technology.

Recovery and Post-extinction Ecosystems

Post-crisis ecosystems show protracted recovery with reef ecosystems eventually rebuilt by new calcifying communities and microbialites, documented in successions across the Canning Basin, Holy Cross Mountains, and Murzuq Basin and studied by field teams from the University of Western Australia and Polish Academy of Sciences. The Famennian sees the rise of novel ammonoid clades and diversification of heterostracan and osteichthyan lineages, informing vertebrate macroevolutionary models developed at the Natural History Museum, London and Smithsonian Institution. Long-term biotic restructuring influenced the trajectory toward Carboniferous faunas and floras associated with coal-bearing strata in the Appalachians and Central European Basin, with paleoecological syntheses advanced by the Paleontological Society and interdisciplinary collaborations among the Royal Society and multiple universities.

Category:Devonian extinctions