Hangenberg

Hangenberg
Name	Hangenberg
Period	Devonian–Carboniferous boundary
Age	Late Famennian–Tournaisian
Type	extinction interval / event horizon
Location	Euramerica, Gondwana, Panthalassa margins
Significance	major marine extinction and global anoxia

Hangenberg The Hangenberg interval is a late Devonian–early Carboniferous geological event documented across Europe, North America, South America, Africa, Asia, and Australia that marks a pronounced faunal turnover, geochemical perturbation, and sedimentary shift. It is recognized in stratigraphic sections such as the Rhenish Massif, Montagne Noire, New York State, Mackenzie Mountains, Cantabria, and East Greenland, and has been tied to broader episodes recorded at the Frasnian–Famennian and Late Devonian crises. The term is commonly applied to an organic-rich horizon, a pronounced extinction pulse among vertebrates and invertebrates, and a suite of geochemical signatures preserved in marine and marginal marine successions.

Geology

The interval is recorded in lithologies ranging from black shales and pelagic limestones to deltaic sandstones and siliciclastic successions in regions such as the Rheinisches Schiefergebirge, Appalachian Basin, Western Canada Sedimentary Basin, Cantabrian Zone, and Gondwanan basins like the Paraná Basin and Karoo Basin. Typical field indicators include condensed beds, phosphatic layers, and widespread organic-rich laminations correlated to sequence stratigraphic surfaces recognized in the International Commission on Stratigraphy frameworks. Tectonostratigraphic settings include passive margins (e.g., Laurentia margins), cratonic basins (e.g., Baltica), and foreland basins influenced by orogens such as the Variscan Orogeny and Alleghanian Orogeny. Petrographic studies often reference diagenetic overprints, clay mineral assemblages, and authigenic pyrite common to anoxic depositional regimes.

Hangenberg Event

The event itself is a geologically brief but biologically severe crisis characterized by a negative excursion in carbon isotopes and a spike in mercury concentrations documented in sections like the Kellwasser Horizon-adjacent successions and the type sections in the Rhenish Massif. It is contemporaneous with extinction signals seen in vertebrate assemblages from Strunian and Silesian successions and with changes in pelagic faunas such as ammonoids and conodonts recorded in global biostratigraphic records maintained by institutions including the Palaeontological Association and stratigraphers from the Geological Society of London.

Stratigraphy and Sedimentology

Stratigraphically, the interval is positioned at the top of the Famennian Stage and at or just below the base of the Tournaisian Stage in the International Chronostratigraphic Chart. It is often recognized by sequence boundaries, maximum flooding surfaces, and condensed successions containing phosphorites and glauconite in shelfal settings like the Paris Basin and North Sea Basin. Sedimentological facies include laminated anoxic shales in basins such as the Carnic Alps and bioturbated sandstones in deltaic provinces comparable to the Hudson Bay Basin. Chemostratigraphy relies on carbonate and organic carbon isotope records, strontium isotope ratios, and trace element proxies measured in cores from agencies such as the United States Geological Survey and British Geological Survey.

Paleontology and Biotic Effects

Biotic effects include substantial losses among placoderm fishes, major turnovers in ammonoid and conodont lineages, and restructuring of benthic faunas including brachiopod and bivalve communities in basins like the Rhenish Massif and Siberian Platform. Vertebrate faunas from sites linked to researchers at the Natural History Museum, London and the Smithsonian Institution show declines in reef-associated taxa commonly discussed alongside reef crises in the Famennian Reef Crisis literature. Phytoplankton and microfossil records, including changes in acritarch and acritarch assemblages, indicate productivity shifts, while trace fossil disappearance in some shelves documents oxygen stress and substrate instability.

Chronology and Global Correlation

Absolute and relative dating integrates biostratigraphy (notably conodont zonations), magnetostratigraphy, and radiometric constraints such as U–Pb zircon ages from ash beds in sections studied by teams at institutions like the Geological Survey of Canada and GFZ Potsdam. The event is correlated globally with contemporaneous black shale deposition in the Canning Basin, Sakmarian predictors in the Ural Mountains, and mercury enrichments in successions sampled by international consortia. Correlations employ index fossils including conodont genera such as Siphonodella and ammonoid markers used by the International Commission on Stratigraphy and various national geological surveys.

Causes and Mechanisms

Proposed mechanisms blend multiple drivers: widespread marine anoxia evidenced by euxinic proxies and pyrite framboid data; rapid climatic perturbations invoking glacio-eustatic sea-level fall and rise linked to polar ice dynamics and transient cooling or warming episodes; and episodes of large igneous province volcanism inferred from mercury anomalies and osmium isotope excursions tied to magmatic provinces like the Carolina Terrane or inferred pulses related to the emplacement histories studied by volcanologists at the United States Geological Survey. Additional hypotheses include terrestrial vegetation collapse affecting silicate weathering and nutrient fluxes, and bolide impact scenarios evaluated against stratigraphic beds and shocked mineral searches conducted by planetary geologists.

Regional Studies and Type Localities

Key type localities and regional studies include classic sections in the Rhenish Massif (type area), the Montagne Noire of southern France, subsurface cores in the Appalachian Basin, outcrops in East Greenland, and coastal sections of Avalonia and Armorica. Regional syntheses have been produced by research groups at universities such as University of Cambridge, University of Oxford, Utrecht University, University of Toronto, and University of Melbourne, and by national surveys including the British Geological Survey and Geological Survey of Canada. Ongoing work integrates paleobiology, sedimentology, and geochemistry to refine the temporal resolution and to resolve remaining debates about causal interplay.

Category:Devonian–Carboniferous events Category:Mass extinctions