Triassic-Jurassic boundary

Triassic-Jurassic boundary
Name	Triassic–Jurassic boundary
Time period	Late Triassic, Early Jurassic
Epoch	Rhaetian–Hettangian
Duration	~201.3 Ma
Major event	End-Triassic extinction

Triassic-Jurassic boundary The Triassic–Jurassic boundary marks a geologic transition near the end of the Triassic and start of the Jurassic. It coincides with the End-Triassic extinction and is studied through stratigraphic sections, radiometric dates, and fossil turnovers recorded in locations such as Rhaetian Stage, Hettangian Stage, and global stratotypes.

Overview

The boundary is characterized by a pronounced faunal and floral turnover documented in classic sections like the St. Audrie's Bay exposures, the Kellerwald sections, and the Newark Basin drill cores alongside marine sections in the Penarth Group and the Klawack Formation. Correlation relies on ammonoid, conodont, and palynological shifts observed in sequences associated with work by researchers from institutions such as the United States Geological Survey, the Natural History Museum, London, and the Geological Survey of Canada. Debate over the formal Global Boundary Stratotype Section and Point has involved proposals from teams at universities including University of Cambridge, University of Oxford, and University of California, Berkeley.

Stratigraphy and Age

Stratigraphic placement uses biostratigraphy anchored to stages like the Rhaetian Stage and Hettangian Stage and radiometric calibrations from U-Pb dating of volcanic ash beds in formations such as the Kroenke Formation and Meishan section analogs. High-precision dates from laboratories at Massachusetts Institute of Technology, ETH Zurich, and Nanjing University constrain the boundary near 201.3 million years ago in timescales promulgated by commissions including the International Commission on Stratigraphy and committees within the International Union of Geological Sciences.

Extinction Event and Biotic Effects

The End-Triassic extinction saw declines in marine and terrestrial groups including many conodont lineages, reef-building coral frameworks, several ammonite families, and non-avian dinosaur competitors, with survival and radiation documented among early theropod clades and early sauropodomorph lineages. Palynological records show losses of certain spore and pollen taxa and opportunistic proliferation of others in datasets curated by researchers affiliated with Smithsonian Institution, Natural History Museum, London, and University of Toronto. Marine extinctions are correlated with changes recorded in sections studied by teams from Geological Survey of Norway, University of Bergen, and University of Lisbon.

Causes and Environmental Changes

Hypotheses for causation include massive volcanism linked to the Central Atlantic Magmatic Province, perturbations in the carbon cycle documented alongside emplacement events studied by groups from Woods Hole Oceanographic Institution and Lamont–Doherty Earth Observatory, and potential bolide impact scenarios proposed by investigators at Imperial College London and Vrije Universiteit Amsterdam. Environmental effects invoked are rapid greenhouse warming, ocean acidification, and deoxygenation evidenced in records gathered by expeditions sponsored by organizations like the National Science Foundation and analyses performed at facilities including Scripps Institution of Oceanography.

Geochemical and Paleoclimatic Evidence

Isotopic excursions in carbon isotopes (δ13C) and mercury anomalies linked to the Central Atlantic Magmatic Province eruptions appear in stratigraphic records analyzed by teams at ETH Zurich, University of Melbourne, and University of Washington. Proxy records from marine carbonate sections, organic-rich shales, and terrestrial lignites studied by researchers from Australian National University and University of São Paulo document shifts in oxygen isotopes, mercury concentrations, and biomarkers that imply rapid warming, enhanced weathering, and changes in vegetation and soil stability across provinces such as the North American Cordillera, European Variscides, and the Amazon Basin margins.

Regional Correlates and Global Stratotypes

Key regional correlates include the radiolarian and conodont sequences in the Tethys Ocean realm, palynological turnovers in the Newark Supergroup rift basins, and marine boundary markers in the Penarth Group of the United Kingdom and comparable successions in the New Zealand strata. Proposals for Global Stratotype Section and Point candidacy have involved sections from the St. Audrie's Bay exposures, sequences near the Krähenberg locality, and candidate sections submitted by consortia including the International Commission on Stratigraphy and national surveys such as the British Geological Survey.

Recovery and Early Jurassic Ecosystems

Following the boundary interval, Early Jurassic ecosystems show diversification of surviving clades, with ammonite radiations documented in collections at museums like the Natural History Museum, London and theropod-sauropodomorph ecological shifts preserved in formations studied by teams from University of Chicago, Yale University, and University of Buenos Aires. Marine reef systems recover with different framework builders, and terrestrial flora sees the spread of ferns and early conifers recorded in archives curated by the Field Museum and the Royal Ontario Museum, marking ecological restructuring that set the stage for Jurassic radiations cataloged by paleontologists at institutions including the American Museum of Natural History and Chinese Academy of Sciences.

Category:Geological boundaries Category:Mass extinctions