Hettangian

Hettangian
Name	Hettangian
Color	#123456
Time start	201.3
Time end	199.3
Time unit	Ma
Preceding	Rhaetian
Following	Sinemurian

Hettangian The Hettangian is the earliest age of the Jurassic Period and the lowermost stage of the Lias. It succeeds the Rhaetian Stage of the Triassic and precedes the Sinemurian; its boundaries are tied to biostratigraphic and radiometric markers used in global stratigraphy by institutions such as the International Commission on Stratigraphy and the International Union of Geological Sciences. The stage has been defined and used in regional stratigraphic schemes across Europe, North America, Asia, and Africa in connection with classic sections in locations including Cucalón-area exposures and the Les Petites Dalles cliffs.

Definition and stratigraphic context

The base of the Hettangian is defined at the first appearance datum of ammonoid taxa such as members of the family Psiloceratidae and by the last occurrences of Triassic index fossils from formations correlated with the K-Pg boundary discussions, with formal ratification processes managed by the International Commission on Stratigraphy and debated in congresses attended by researchers from institutions like University of Cambridge, University of Oxford, Sorbonne University, and University of California, Berkeley. The stage correlates with biozones recognized in the Posidonia Shale regional scheme, ties into magnetostratigraphic chrons established at observatories such as the British Geological Survey and the United States Geological Survey, and is integrated with chemostratigraphic datasets developed by teams at ETH Zurich and Massachusetts Institute of Technology.

Geology and lithostratigraphy

Hettangian successions are characterized by marine and marginal marine lithofacies recorded in numerous formations including the Lias Group exposures of England, the Grès à Voltzia-type sandstones of France, the Calvera Formation analogs of Spain, and comparable sequences in the Newark Supergroup basins of North America. Key lithologies include shales, limestones, marls, and siliciclastic beds studied by geologists at Imperial College London, University of Bonn, Peking University, and the Naturhistorisches Museum Wien. Stratigraphic columns incorporate sequence stratigraphy concepts refined in collaborations among the Geological Society of London, the European Geosciences Union, and the American Geophysical Union, and correlate with volcaniclastic marker horizons tied to eruptive events recorded by investigators affiliated with USGS Volcano Hazards Program and Geological Survey of Japan.

Paleontology and fossil record

Fossil assemblages from Hettangian strata include ammonoids, bivalves, brachiopods, marine reptiles such as Ichthyosauria and Plesiosauria, early representatives of Theropoda and Sauropodomorpha dinosaurs found by teams from Natural History Museum, London, Smithsonian Institution, Muséum National d'Histoire Naturelle, and Royal Belgian Institute of Natural Sciences, as well as flora remains like bennettitaleans and early conifers examined at Royal Botanic Gardens, Kew and the New York Botanical Garden. Palynological and microfossil studies by researchers at Woods Hole Oceanographic Institution and Scripps Institution of Oceanography document spore, pollen, foraminiferal, and nannofossil turnover across the Triassic–Jurassic transition, informing debates involving paleobiologists from University of Chicago and Max Planck Institute for Evolutionary Anthropology about survivorship patterns after extinction events.

Paleoclimate and paleoenvironment

Paleoenvironmental reconstructions for the Hettangian employ stable isotope records, paleomagnetic data, and climate models developed at NASA Goddard Institute for Space Studies, Lamont–Doherty Earth Observatory, Centre National de la Recherche Scientifique, and University of Copenhagen. These indicate episodes of oceanic anoxia reflected in organic-rich shales akin to those in the Posidonia Shale Formation and suggest transient greenhouse conditions debated in studies by teams from University of Leeds, University of Oslo, and University of Barcelona. Terrestrial sections document facies indicative of seasonal rainfall patterns and floodplain dynamics comparable to records from Karoo Basin studies and research programs conducted by South African National Parks scientists.

Chronostratigraphic correlations and dating

Absolute and relative dating of Hettangian deposits integrates high-precision U-Pb zircon geochronology performed at laboratories such as Geological Survey of Canada and ETH Zurich, alongside biostratigraphic zonations using ammonite and conodont frameworks established by scholars affiliated with Senckenberg Gesellschaft für Naturforschung and Naturhistorisches Museum Basel. Correlations link Hettangian chronostratigraphy with magnetostratigraphic polarity timescales used by the International Ocean Discovery Program and calibrated with radiometric ages reported in journals involving contributors from Geological Society of America and American Association of Petroleum Geologists.

Historical research and naming

The stage name derives from exposures near Hettange-Grande in France, first described by 19th-century geologists who worked with institutions such as the Muséum National d'Histoire Naturelle and corresponded with contemporaries at Royal Society. Nineteenth- and twentieth-century stratigraphers including those associated with University of Göttingen, University of Vienna, and the British Museum refined the concept through field studies, museum collections, and the establishment of reference sections, leading to modern codification by the International Commission on Stratigraphy and adoption in global geological time scales endorsed by the International Union of Geological Sciences.

Category:Jurassic stages