Triassic–Jurassic extinction event

Triassic–Jurassic extinction event
Name	Triassic–Jurassic extinction event
Time period	Late Triassic, Early Jurassic
Approx age	~201.3 million years ago
Possible causes	Central Atlantic magmatic province, climate change, ocean anoxia, asteroid impact
Major losses	marine reptiles, large amphibians, many synapsids, diverse archosaur lineages

Triassic–Jurassic extinction event was a major biotic crisis at the boundary between the Triassic and Jurassic periods that profoundly reshaped Mesozoic ecosystems. It coincides with volcanism in the Central Atlantic magmatic province, rearrangements of continental plates such as Pangaea, and faunal turnovers that paved the way for dinosaur dominance and influenced marine and terrestrial clades. The event is recorded in stratigraphic sections correlated with magnetostratigraphy, radiometric dates, and chemostratigraphic signals used by paleontologists, geologists, and geochemists.

Overview and Timing

The extinction horizon is placed at the end of the Rhaetian and the base of the Hettangian, dated with high-precision U–Pb dating of zircon from Central Atlantic magmatic province flows and interbedded tuffs; correlations draw on sections from the Newark Basin, Karoo Basin, Morocco, England, and Greenland. Biostratigraphic markers such as ammonoid turnovers linked to studies by workers at institutions including the Natural History Museum, London and the Smithsonian Institution help refine timing alongside analyses published in journals like Nature and Science. Magnetostratigraphy tied to the Geomagnetic Polarity Time Scale assists in correlating disparate localities from the Tethys Ocean margins to Panthalassan shelves.

Causes and Mechanisms

Hypotheses invoke rapid volcanism associated with the Central Atlantic magmatic province as a primary driver; massive basalt emplacement released greenhouse gases traced in studies by researchers affiliated with University of California, University of Oxford, and University of Toronto. Degassing of CO2 and SO2 led to greenhouse warming and acidification detected in carbonate platform records from Italy, Portugal, and Canada. Secondary mechanisms include episodes of oceanic anoxia inferred from black shale intervals comparable to deposits studied in the Fossil Butte Member and the Kennecott Formation, and proposed extraterrestrial causes debated since analogies to the Chicxulub crater research for the Cretaceous–Paleogene extinction event were raised. Feedbacks involving methane clathrate dissociation, modeled by teams at the Max Planck Institute for Chemistry and the Jet Propulsion Laboratory, could have amplified warming while ozone depletion hypotheses draw on comparisons with Permian–Triassic extinction event studies.

Biotic Impacts and Extinctions

Marine realms show extinctions among conodont assemblages, diverse ammonoid lineages, and reef builders including calcimicrobe communities recorded in the Newark Supergroup and British Columbia sequences; bivalve and gastropod faunas were selectively reduced. Terrestrial losses included large temnospondyl amphibians documented in the Karoo Basin and several synapsid groups cataloged in collections at the American Museum of Natural History; conversely, archosaurian lineages such as early Crocodylomorpha and basal Dinosauria experienced turnover enabling adaptive radiations studied by paleontologists at Harvard University and University of Bristol. Plant communities show shifts from glossopterid-dominated floras recorded in Antarctica and Australia to fern and gymnosperm assemblages captured in floras curated at the Field Museum.

Environmental and Climatic Changes

Proxy records indicate rapid warming, sea-level fluctuations, and episodes of ocean anoxia. Isotopic excursions in carbon and oxygen from carbonate and organic records at localities in Greenland, Spain, Morocco, and the Canadian Arctic reveal perturbations similar in scale to those studied across the Eocene–Oligocene and Paleocene–Eocene Thermal Maximum. Sedimentological evidence from the Newark Basin documents flood basalt-related environmental stress, while mercury anomalies correlated to Central Atlantic magmatic province eruptions appear in cores analyzed by teams at Woods Hole Oceanographic Institution and Scripps Institution of Oceanography. Changes to hydrological cycles and increased aridity in interior basins are inferred from palynological shifts investigated by researchers at Utrecht University and University of Heidelberg.

Recovery and Evolutionary Consequences

After the crisis, ecological vacuums allowed diversification of dinosaurs, early mammals, and new marine reptiles; this recovery is reconstructed from fossil-bearing formations such as the Kayenta Formation, Lias Group, and strata in the Jura Mountains. Radiations of theropods, sauropodomorphs, and early ornithischians documented by scientists at University of Chicago and University of Bonn illustrate pathways to Mesozoic dominance. Plant recovery favored ferns and conifers preserved in collections at the Natural History Museum of Denmark, with conodont- and ammonite-driven marine ecosystems reassembling into new trophic structures analogous to patterns seen after the Permian–Triassic extinction event.

Evidence and Geological Record

Multiple lines of evidence support the extinction pulse: stratigraphic gaps and turnover in marine biota from sections in the Araripe Basin and Newfoundland; geochemical markers including negative carbon isotope excursions preserved in carbonate sections studied by teams at ETH Zurich and University of California, Berkeley; stratigraphic mercury enrichments linked to large igneous province activity reported by researchers at Geological Survey of Canada; and radiometric ages from U–Pb zircon that synchronize biotic and volcanic events in the Central Atlantic magmatic province. Paleontological datasets compiled in museums such as the Natural History Museum, Vienna and analytic approaches developed at the University of Tokyo continue to refine the spatial and temporal pattern of extinctions across marine shelves, continental basins, and island arcs.

Category:Extinction events