The Olenekian saw the deposition of a large part of theBuntsandstein in Europe. The Olenekian is roughly coeval with the regional Yongningzhenian Stage used inChina.
The Olenekian Stage was introduced into scientific literature by Russian stratigraphers in 1956.[9] The stage is named afterOlenëk inSiberia. Before the subdivision in Olenekian and Induan became established, both stages formed the Scythian Stage, which has since disappeared from the official timescale.
In the 1960s, English paleontologistEdward T. Tozer (sometimes collaborating with American geologist Norman J. Silberling) crafted Triassic timescales based on North American ammonoid zones, further refining it in the following decades. Tozer's nomenclature was largely derived fromMojsisovics's work, who coined most of the Triassic stages and substages, but he redefined them using North American sites. He recommended the Lower Triassic series be divided into the Griesbachian, Dienerian, Smithian, and Spathian. The latter two roughly correspond with the Olenekian. Tozer's timescale became popular in the Americas.[10] He named the Smithian after Smith Creek onEllesmere Island, Canada (the creek itself is named after geologistJ. P. Smith). The Smithian is defined by theArctoceras bloomstrandi ammonoid zone (containsEuflemingites romunderi andJuvenites crassus) and the overlyingMeekoceras gracilitatis andWasatchites tardus subzones. He named the Spathian after Spath Creek on Ellesmere Island (this creek is named after geologistL. F. Spath), and defined it by theProcolumbites subrobustus ammonoid zone.[8]
In the oceans,microbial reefs were common during the Early Triassic, possibly due to lack of competition withmetazoan reef builders as a result of the extinction.[13] However, transient metazoan reefs reoccurred during the Olenekian wherever permitted by environmental conditions.[14]Ammonoids andconodonts diversified, but both suffered losses during the Smithian-Spathian boundary extinction (see below)[15] at the end of the Smithian subage.
The terrestrialflora was also affected significantly, changing fromlycopod-dominated (e.g.Pleuromeia) during theDienerian and Smithian subages togymnosperm- andpteridophyte-dominated in the Spathian.[45][12] These vegetation changes are due to global changes in temperature andprecipitation.Conifers (gymnosperms) were the dominant plants during most of theMesozoic. Until recently[when?] the existence of this extinction event about 249.4 Ma ago[46] was not recognised.[47]
The Smithian–Spathian boundary extinction was linked to late eruptions of theSiberian Traps,[48][49] which released warminggreenhouse gases, resulting in global warming[50] and in acidification, both on land[51] and in the ocean.[52][53] A large spike inmercury concentrations relative to total organic carbon, much like during the Permian-Triassic extinction, has been suggested as another contributor to the extinction,[54] although this is controversial and has been disputed by other research that suggests elevated mercury levels already existed by the middle Smithian.[55] Prior to the Smithian-Spathian Boundary extinction event, a flatgradient of latitudinal species richness is observed, suggesting that warmer temperatures extended into higherlatitudes, allowing extension of geographic ranges of species adapted to warmer temperatures, and displacement or extinctions of species adapted to cooler temperatures.[43]Oxygen isotope studies on conodonts have revealed that temperatures rose in the first 2 million years of the Triassic, ultimately reachingsea surface temperatures of up to 40 °C (104 °F) in the tropics during the Smithian.[56] The extinction itself occurred during a subsequent drop in global temperatures (ca. 8°C over a geologically short period) in the latest Smithian; however, temperature alone cannot account for the Smithian-Spathian boundary extinction, because several factors were at play.[12][46] An alternative explanation for the extinction event hypothesises the biotic crisis took place not at the Smithian-Spathian boundary but shortly before, during the Late Smithian Thermal Maximum (LSTM), with the Smithian-Spathian boundary itself being associated with cessation of intrusive magmatic activity of the Siberian Traps,[57] along with significant global cooling,[58][59] after which a gradual biotic recovery took place over the early and middle Spathian,[57] along with a decline in continental weathering[60] and a rejuvenation of ocean circulation.[61]
In the ocean, many large and mobile species moved away from thetropics, but large fish remained,[28] and amongst the immobile species such asmolluscs, only the ones that could cope with the heat survived; half thebivalves disappeared.[62] Conodonts decreased in average size as a result of the extinction.[63] On land, the tropics were nearly devoid of life,[64] with exceptionally arid conditions recorded in Iberia and other parts of Europe then at low latitude.[65] Many big, activeanimals returned to the tropics, and plants recolonised on land, only when temperatures returned to normal.
There is evidence that life had recovered rapidly, at least locally. This is indicated by sites that show exceptionally high biodiversity (e.g. the earliest SpathianParis Biota),[37][38] which suggest thatfood webs were complex and comprised severaltrophic levels.
^McElwain, J. C.; Punyasena, S. W. (2007). "Mass extinction events and the plant fossil record".Trends in Ecology & Evolution.22 (10):548–557.doi:10.1016/j.tree.2007.09.003.PMID17919771.
^Lucas, S. G. (2010). "The Triassic chronostratigraphic scale: history and status".Geological Society, London, Special Publications.334 (1):17–39.Bibcode:2010GSLSP.334...17L.doi:10.1144/sp334.2.
^Brayard, Arnaud; Vennin, Emmanuelle; Olivier, Nicolas; Bylund, Kevin G.; Jenks, Jim; Stephen, Daniel A.; Bucher, Hugo; Hofmann, Richard; Goudemand, Nicolas; Escarguel, Gilles (18 September 2011). "Transient metazoan reefs in the aftermath of the end-Permian mass extinction".Nature Geoscience.4 (10):693–697.Bibcode:2011NatGe...4..693B.doi:10.1038/ngeo1264.
^Galfetti, Thomas; Hochuli, Peter A.; Brayard, Arnaud; Bucher, Hugo; Weissert, Helmut; Vigran, Jorunn Os (2007). "Smithian-Spathian boundary event: Evidence for global climatic change in the wake of the end-Permian biotic crisis".Geology.35 (4): 291.Bibcode:2007Geo....35..291G.doi:10.1130/G23117A.1.
^Stensiö, Erik (1932). "Triassic Fishes from East Greenland collected by the Danish expeditions in 1929-1931".Meddelelser om Grønland.83 (3):1–305.OCLC938169014.
^Nielsen, Eigil (1936). "Some few preliminary remarks on Triassic fishes from East Greenland".Meddelelser om Grønland.112 (3):1–55.
^Beltan, Laurence (1996). "Overview of systematics, paleobiology, and paleoecology of Triassic fishes of northwestern Madagascar". In G. Arratia; G. Viohl (eds.).Mesozoic Fishes—Systematics and Paleoecology. München: Dr. Friedrich Pfeil. pp. 479–500.
^Romano, Carlo; López-Arbarello, Adriana; Ware, David; Jenks, James F.; Brinkmann, Winand (April 2019). "Marine Early Triassic Actinopterygii from the Candelaria Hills (Esmeralda County, Nevada, USA)".Journal of Paleontology.93 (5):971–1000.Bibcode:2019JPal...93..971R.doi:10.1017/jpa.2019.18.
^abStensiö, E. (1921).Triassic fishes from Spitzbergen 1. Wien: Adolf Holzhausen. pp. xxviii+307.
^Stensiö, E. (1925). "Triassic fishes from Spitzbergen 2".Kungliga Svenska Vetenskapsakademiens Handlingar.3:1–261.
^Kogan, Ilja; Romano, Carlo (2016). "A new postcranium of Saurichthys from the Early Triassic of Spitsbergen".Freiberger Forschungshefte, Reihe C:205–222.doi:10.5167/uzh-136748.
^Cavin, L.; Argyriou, T.; Romano, C.; Grădinaru, E. (2024). "Large durophagous fish from the Spathian (late Early Triassic) of Romania hints at earlier onset of the Triassic actinopterygian revolution".Papers in Palaeontology.10 (2). e1553.Bibcode:2024PPal...10E1553C.doi:10.1002/spp2.1553.
^Romano, Carlo; Brinkmann, Winand (December 2010). "A new specimen of the hybodont shark Palaeobates polaris with threedimensionally preserved Meckel's cartilage from the Smithian (Early Triassic) of Spitsbergen".Journal of Vertebrate Paleontology.30 (6):1673–1683.Bibcode:2010JVPal..30.1673R.doi:10.1080/02724634.2010.521962.
^Bratvold, Janne; Delsett, Lene Liebe; Hurum, Jørn Harald (2018-10-04). "Chondrichthyans from theGrippia bonebed (Early Triassic) of Marmierfjellet, Spitsbergen".Norwegian Journal of Geology.98 (2):189–217.doi:10.17850/njg98-2-03.hdl:10852/71103.
^Mutter, Raoul J.; Neuman, Andrew G. (2008). "New eugeneodontid sharks from the Lower Triassic Sulphur Mountain Formation of Western Canada". In Cavin, L.; Longbottom, A.; Richter, M. (eds.).Fishes and the Break-up of Pangaea. Geological Society of London, Special Publications. Vol. 295. London: Geological Society of London. pp. 9–41.doi:10.1144/sp295.3.
^Iniesto, Miguel; Thomazo, Christophe; Fara, Emmanuel (June 2019). "Deciphering the exceptional preservation of the Early Triassic Paris Biota (Bear Lake County, Idaho, USA)".Geobios.54:81–93.doi:10.1016/j.geobios.2019.04.002.
^Galfetti, Thomas; Hochuli, Peter A.; Brayard, Arnaud; Bucher, Hugo; Weissert, Helmut; Vigran, Jorunn Os (2007). "Smithian-Spathian boundary event: Evidence for global climatic change in the wake of the end-Permian biotic crisis".Geology.35 (4): 291.Bibcode:2007Geo....35..291G.doi:10.1130/G23117A.1.
^Zhang, Lei; Orchard, Michael J.; Brayard, Arnaud; Algeo, Thomas J.; Zhao, Laishi; Chen, Zhong-Qiang; Lyu, Zhengyi (August 2019). "The Smithian/Spathian boundary (late Early Triassic): A review of ammonoid, conodont, and carbon-isotopic criteria".Earth-Science Reviews.195:7–36.Bibcode:2019ESRv..195....7Z.doi:10.1016/j.earscirev.2019.02.014.
^abBrayard, Arnaud; Bucher, Hugo; Escarguel, Gilles; Fluteau, Frédéric; Bourquin, Sylvie; Galfetti, Thomas (September 2006). "The Early Triassic ammonoid recovery: paleoclimatic significance of diversity gradients".Palaeogeography, Palaeoclimatology, Palaeoecology.239 (3–4):374–395.Bibcode:2006PPP...239..374B.doi:10.1016/j.palaeo.2006.02.003.
^Du, Yong; Song, Huyue; Algeo, Thomas J.; Song, Haijun; Tian, Li; Chu, Daoliang; Shi, Wei; Li, Chao; Tong, Jinnan (1 August 2022). "A massive magmatic degassing event drove the Late Smithian Thermal Maximum and Smithian–Spathian boundary mass extinction".Global and Planetary Change.215: 103878.Bibcode:2022GPC...21503878D.doi:10.1016/j.gloplacha.2022.103878.
^Paton, M. T.; Ivanov, A. V.; Fiorentini, M. L.; McNaughton, M. J.; Mudrovska, I.; Reznitskii, L. Z.; Demonterova, E. I. (1 September 2010). "Late Permian and Early Triassic magmatic pulses in the Angara–Taseeva syncline, Southern Siberian Traps and their possible influence on the environment".Russian Geology and Geophysics.51 (9):1012–1020.Bibcode:2010RuGG...51.1012P.doi:10.1016/j.rgg.2010.08.009.
^Romano, Carlo; Goudemand, Nicolas; Vennemann, Torsten W.; Ware, David; Schneebeli-Hermann, Elke; Hochuli, Peter A.; Brühwiler, Thomas; Brinkmann, Winand; Bucher, Hugo (21 December 2012). "Climatic and biotic upheavals following the end-Permian mass extinction".Nature Geoscience.6 (1):57–60.doi:10.1038/ngeo1667.
^Borruel-Abadía, Violeta; Barrenechea, José F.; Galán-Abellán, Ana Belén; De la Horra, Raúl; López-Gómez, José; Ronchi, Ausonio; Luque, Francisco Javier; Alonso-Azcárate, Jacinto; Marzo, Mariano (20 June 2019). "Could acidity be the reason behind the Early Triassic biotic crisis on land?".Chemical Geology.515:77–86.Bibcode:2019ChGeo.515...77B.doi:10.1016/j.chemgeo.2019.03.035.
^Ye, Feihong; Zhao, Laishi; Zhang, Lei; Cui, Ying; Algeo, Thomas J.; Chen, Zhong-Qiang; Lyu, Zhengyi; Huang, Yuangeng; Bhat, Ghulam M.; Baud, Aymon (August 2023). "Calcium isotopes reveal shelf acidification on southern Neotethyan margin during the Smithian-Spathian boundary cooling event".Global and Planetary Change.227: 104138.Bibcode:2023GPC...22704138Y.doi:10.1016/j.gloplacha.2023.104138.
^Song, Haijin; Song, Huyue; Tong, Jinnan; Gordon, Gwyneth W.; Wignall, Paul B.; Tian, Li; Zheng, Wang; Algeo, Thomas J.; Liang, Lei; Bai, Ruoyu; Wu, Kui; Anbar, Ariel D. (20 February 2021). "Conodont calcium isotopic evidence for multiple shelf acidification events during the Early Triassic".Chemical Geology.562: 120038.Bibcode:2021ChGeo.56220038S.doi:10.1016/j.chemgeo.2020.120038.
^Song, Huyue; Tong, Jinnan; Algeo, Thomas J.; Koracek, Micha; Qiu, Haiou; Song, Haijun; Tian, Li; Chen, Zhong-Qiang (June 2013). "Large vertical δ13CDIC gradients in Early Triassic seas of the South China craton: Implications for oceanographic changes related to Siberian Traps volcanism".Global and Planetary Change.105:7–20.Bibcode:2013GPC...105....7S.doi:10.1016/j.gloplacha.2012.10.023.
^Chen, Yanlong; Richoz, Sylvain; Krystyn, Leopold; Zhang, Zhifei (August 2019). "Quantitative stratigraphic correlation of Tethyan conodonts across the Smithian-Spathian (Early Triassic) extinction event".Earth-Science Reviews.195:37–51.Bibcode:2019ESRv..195...37C.doi:10.1016/j.earscirev.2019.03.004.
^Sun, Y.; Joachimski, M. M.; Wignall, P. B.; Yan, C.; Chen, Y.; Jiang, H.; Wang, L.; Lai, X. (18 October 2012). "Lethally Hot Temperatures During the Early Triassic Greenhouse".Science.338 (6105):366–370.Bibcode:2012Sci...338..366S.doi:10.1126/science.1224126.PMID23087244.
^Lloret, Joan; De la Hora, Raúl; Gretter, Nicola; Borruel-Abadía, Violeta; Barrenechea, José F.; Ronchi, Ausonio; Diez, José B.; Arche, Alfredo; López-Gómez, José (September 2020). "Gradual changes in the Olenekian-Anisian continental record and biotic implications in the Central-Eastern Pyrenean basin, NE Spain".Global and Planetary Change.192: 103252.Bibcode:2020GPC...19203252L.doi:10.1016/j.gloplacha.2020.103252.
Kiparisova, L.D. & Popov, J.N.;1956:Расчленение нижнего отдела триасовой системы на ярусы (Subdivision of the lower series of the Triassic System into stages),Doklady Akademii Nauk SSSR109(4), pp 842–845(in Russian).
