The Induan is the first age of the Early Triassic epoch in the geologic timescale, or the lowest stage of the Lower Triassic series in chronostratigraphy. It spans the time between 251.902 Ma and 251.2 Ma (million years ago).[8] The Induan is sometimes divided into the Griesbachian and the Dienerian subages or substages.[9] The Induan is preceded by the Changhsingian (latest Permian) and is followed by the Olenekian.

251.902 ± 0.024 – 251.2 Ma
Lower Limestone and Shale Member, Mikin Formation, Mud (Spiti).jpg
Induan aged rock layers of the Mikin Formation (Lahaul and Spiti district, India)
Name formalityFormal
Usage information
Celestial bodyEarth
Regional usageGlobal (ICS)
Time scale(s) usedICS Time Scale
Chronological unitAge
Stratigraphic unitStage
Time span formalityFormal
Lower boundary definitionFAD of the Conodont Hindeodus parvus
Lower boundary GSSPMeishan, Zhejiang, China
31°04′47″N 119°42′21″E / 31.0798°N 119.7058°E / 31.0798; 119.7058
GSSP ratified2001[6]
Upper boundary definitionNot formally defined
Upper boundary definition candidatesFAD of the Conodont Neospathodus waageni
Upper boundary GSSP candidate section(s)Mud (Muth) village, Spiti valley, India[7]

The Induan is roughly coeval with the regional Feixianguanian Stage of China.



The Triassic is the first period of the Mesozoic era. It is subdivided into the Lower, Middle, and Upper Triassic series, which are further subdivided into stages. The Induan is the first stage of the Lower Triassic, from 251.9 million to 251.2 million years ago, spanning the first 700,000 years after the Permian–Triassic extinction event.[10]

Stages can be defined globally or regionally. For global stratigraphic correlation, the International Commission on Stratigraphy (ICS) ratifies global stages based on a Global Boundary Stratotype Section and Point (GSSP) from a single formation (a stratotype) identifying the lower boundary of the stage. The GSSP for the Induan is defined as the bottom of Bed 27c of the Meishan Section, China, 31°4′47.28″N 119°42′20.9″E / 31.0798000°N 119.705806°E / 31.0798000; 119.705806, with the appearance of the conodont Hindeodus parvus as its primary marker (biostratigraphy), and minimum zones (negative anomalies) of 13C and 18O (corresponding to the extinction event) as its secondary marker. Bed 27c comprises a medium-bedded section of limestone, overlain by clay and a medium-bedded section of dolomitic, argillaceous calcimicrite.[11] Calcimicrite is a type of limestone that contains more micrite than allochem, and the diameter of any particle measures less than 20 microns.[12]

The Induan is succeeded by the Olenekian, whose GSSP is defined at the bottom of Bed A-2 of the Mikin Formation near Mud village, Spiti, India, with the appearance of the conodont Neospathodus waageni and a 13C peak.[13]


There have been several propositions for the organization of the Triassic timescale. Most of the Triassic stages and sub-stages, which are still used today, were coined in an 1895 publication by Austro-Hungarian geologist Johann August Georg Edmund Mojsisovics von Mojsvar, Austrian geologist Carl Diener, and German geologist Wilhelm Heinrich Waagen. They were defined using ammonite research conducted in large part by Mojsisovics and Diener in primarily Austria, Italy, and Bosnia; as well as Waagen's work in the Pakistani Salt Range. They divided the Triassic into four series (from lowest to highest): the Scythian, Dinaric, Tyrolean, and Bavarian. The Scythian was divided (from lowest to highest) into the Brahmanian and Jakutian stages. The Brahmanian's lower boundary was defined by the appearance of the ammonite Otoceras woodwardi in the Himalayas (Austrian paleontologist Carl Ludolf Griesbach had already proposed this ammonite demarcate the beginning of the Triassic in 1880), and its upper boundary by a section of sandstone in the Salt Range characterized by ceratite ammonites.[14][15]

In 1956, Soviet paleontologists Lubov D. Kiparisova and Yurij N. Popov decided to divide the Lower Triassic series into, what they coined, the Induan and Olenekian stages.[16] The Induan honors the Indus River, as they also bounded it using the same criteria and sites as Mojsisovics' Brahmanian in the Indus region, though they resided in Siberia at the time. That is, the Induan is synonymous with the Brahmanian.[15]

In the 1960s, English paleontologist Edward 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), based on the works of Frank McLearn in British Columbia and Siemon Muller in Nevada who pieced together the ammonoid fossil record of the North American Cordillera. Tozer's nomenclature was largely derived from Mojsvar's work, but he redefined them using North American sites. He recommended the Lower Triassic series be divided into the: Griesbachian, Dienerian, Smithian, and Spathian. The former two roughly correspond with the Induan. Tozer's timescale became popular in the Americas.[15] He named the Griesbachian after Griesbach Creek on Axel Heiberg Island, Canada, and further split it into the Gangetian and Ellesmarian substages; the former he defined by the ammonite zones of O. concavum and O. boreale, and the latter by Ophicera commune and Proptychites striatus. He named the Dienerian after Diener Creek on Ellesmere Island, Canada, and defined it by the ammonite zones P. candus and Vavilovites sverdrupi.[17]

In the 1970s, the ICS was founded to globally standardize stratigraphy. They erected the Subcommission on Triassic Stratigraphy (STS), which published its first timescale to Triassic stratigraphy in 1985. They divided it into the Lower, Middle, and Upper series; the Lower Triassic divided into the Induan and Olenekian stages; and the Induan further divided into the Griesbachian and Dienerian substages. In a revised 1991 timescale, they dropped several more of Tozer's considerations, and likewise did away with Induan substages entirely, though Tozer's original definition of them are still in use in ammonoid research.[15]

By the 1990s, most geologists had moved away from ammonite zones, preferring conodonts. Consequently, in 1996, the STS moved the Induan's GSSP to Meishan, China, with the appearance of H. parvus. It was the first GSSP approved by the STS.[15]


Paleoclimatic reconstruction of Pangea during the Induan

During the Induan, all major landmasses had already amalgamated into the supercontinent Pangea, the northern portion referred to as Laurentia, and the southern portion Gondwana. At this point in time, the South Pole was near but not on Antarctica. Eastern Gondwana lay south of the 60°S, and the western part north.[18]

A major rifting zone existed on Madagascar, which was wedged in between the African and the Indian Plate, gradually pushing them apart. This action would expand the newly forming Neo-Tethys Ocean at the expense of the Paleo-Tethys Ocean. Behind the burgeoning Neo-Tethys lay a major rift pushing India away from western Australia, which promulgated volcanoes across the area. During the extinction event, this volcanic activity created the Panjal Traps. In eastern Australia, the Hunter-Bowen orogeny and related magmatic activity was shutting down.[18]

Induan lifeEdit

Fossils of Claraia clarai

The Induan followed the Permian–Triassic extinction event, and historically, it was thought recovery was delayed by as much as five million years to the Middle Triassic. The 21st century discoveries of diverse arrays of conodonts, ammonoids, bivalves, benthic foraminifera, and other ichnotaxa serve to suggest that recovery instead took under 1.5 million years.

The Induan age followed the mass extinction event at the end of the Permian period. Both global biodiversity and community-level (alpha) diversity remained low through much of this stage of the Triassic.[19] Marine black shale deposits are common especially in the Dienerian substage of the Induan. These point to low oxygenation in the ocean.[20]

Much of the supercontinent Pangea remained almost lifeless, deserted, hot, and dry. In higher latitudes, the flora during the Griesbachian was gymnosperm dominated but became lycopod dominated (e.g. Pleuromeia) in the Dienerian.[21] This change reflects a shift in global climate from cool and dry in the Griesbachian to hot and humid in the Dienerian and points to an extinction event during the Induan, c. 500,000 years after the end-Permian mass extinction event.[22] It led to the extinction of the Permian Glossopteris flora.

The lystrosaurids and the proterosuchids were the only groups of land animals to dominate during the Induan Stage. Other animals, such as the ammonoids, insects, and the tetrapods (cynodonts, amphibians, reptiles, etc.) remained rare and terrestrial ecosystems did not recover for some 30 million years.[19] Both the seas and much of the freshwater during the Induan were anoxic, predominantly during the Dienerian subage.[20] Microbial reefs were common, possibly due to lack of competition with metazoan reef builders as a result of the extinction.[23]

Ray-finned fishes largely remained unaffected by the Permian-Triassic extinction event.[24][25] Many genera show a cosmopolitan (worldwide) distribution during the Induan and Olenekian (e.g. Australosomus, Birgeria, Parasemionotidae, Pteronisculus, Ptycholepidae, Saurichthys). This is well exemplified in the Griesbachian aged fish assemblages of the Wordie Creek Formation (East Greenland), the Dienerian aged assemblages of the Sakamena Formation (Madagascar), Candelaria Formation (Nevada, United States), and Mikin Formation (Himachal Pradesh, India), and the Smithian (Olenekian) aged assemblages of the Vikinghøgda Formation (Spitsbergen, Norway), Thaynes Formation (western United States), and Helongshan Formation (Anhui, China). Induan Chondrichthyans include hybodonts, neoselachians and a few surviving lineages of eugeneodontid holocephalians, a mainly Palaeozoic group. Cartilaginous fishes were seemingly rare during the Induan.

Crocodile-shaped, marine temnospondyl amphibians (e.g. Aphaneramma, Wantzosaurus) were geographically widespread during the Induan and Olenekian ages. Their fossils are found in Greenland, Spitsbergen, Pakistan and Madagascar.[26]

The bivalve Claraia was widespread and common in the Panthalassa and Tethys oceans. The geologically oldest oysters (Liostrea) are known from the Induan. They grew on the shells of living ammonoids.[27]

See alsoEdit


  1. ^ Widmann, Philipp; Bucher, Hugo; Leu, Marc; et al. (2020). "Dynamics of the Largest Carbon Isotope Excursion During the Early Triassic Biotic Recovery". Frontiers in Earth Science. 8 (196): 196. Bibcode:2020FrEaS...8..196W. doi:10.3389/feart.2020.00196.
  2. ^ 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. PMID 17919771.
  3. ^ Retallack, G. J.; Veevers, J.; Morante, R. (1996). "Global coal gap between Permian–Triassic extinctions and middle Triassic recovery of peat forming plants". GSA Bulletin. 108 (2): 195–207. Bibcode:1996GSAB..108..195R. doi:10.1130/0016-7606(1996)108<0195:GCGBPT>2.3.CO;2. Retrieved 2007-09-29.
  4. ^ Payne, J. L.; Lehrmann, D. J.; Wei, J.; Orchard, M. J.; Schrag, D. P.; Knoll, A. H. (2004). "Large Perturbations of the Carbon Cycle During Recovery from the End-Permian Extinction". Science. 305 (5683): 506–9. Bibcode:2004Sci...305..506P. doi:10.1126/science.1097023. PMID 15273391. S2CID 35498132.
  5. ^ Ogg, James G.; Ogg, Gabi M.; Gradstein, Felix M. (2016). "Triassic". A Concise Geologic Time Scale: 2016. Elsevier. pp. 133–149. ISBN 978-0-444-63771-0.
  6. ^ Hongfu, Yin; Kexin, Zhang; Jinnan, Tong; Zunyi, Yang; Shunbao, Wu (June 2001). "The Global Stratotype Section and Point (GSSP) of the Permian-Triassic Boundary" (PDF). Episodes. 24 (2): 102–114. doi:10.18814/epiiugs/2001/v24i2/004. Retrieved 8 December 2020.
  7. ^ "Global Boundary Stratotype Section and Point". International Commission of Stratigraphy. Retrieved 23 December 2020.
  8. ^ "ICS - Chart/Time Scale". Archived from the original on 2014-05-30. Retrieved 2017-09-28.
  9. ^ Tozer E. T. (1965): Lower Triassic stages and ammonoid zones of Arctic Canada: Paper of the Geological Survey of Canada 65:1–14.
  10. ^ "International Chronostratigraphic Chart" (PDF). International Commission on Stratigraphy. Retrieved 25 August 2022.
  11. ^ "GSSP for Induan Stage". International Commission on Stratigraphy. Retrieved 16 June 2022.
  12. ^ Bates, R. L.; Jackson, J. A. (1984). Dictionary of Geological Terms. Anchor Press / Doubleday. p. 70. ISBN 978-0-385-18101-3.
  13. ^ "Global Boundary Stratotype Section and Points". International Commission on Stratigraphy. Retrieved 16 June 2022.
  14. ^ Mojsisovics, E.; Waagen, W. H.; Diener, C. "Entwurf einer Gliederung der pelagischen Sediments des Trias-Systems" [Outline of a classification of the pelagic sediments of the Triassic system]. Vienna Academy of Sciences, Mathematical and Scientific Class Meeting Reports (in German). 104: 1279–1302.
  15. ^ a b c d e Lucas, S. G. (2010). "The Triassic chronostratigraphic scale: history and status". Geological Society, London, Special Publications. 334 (1): 17–39. doi:10.1144/sp334.2. S2CID 129648527.
  16. ^ Kiparisova, L. D.; Popov, Y. N. (1956). "Raschlenenie nizhnego otdela triasovoy sistemy na yarusy" [Subdivision of the Lower series of the Triassic System into stages]. Proceedings of the USSR Academy of Sciences (in Russian). 109: 842–845.
  17. ^ Tozer, E. T. (1965). "Lower Triassic stages and ammonoid zones of Arctic Canada". Geological Survey of Canada Paper. 65–12: 1–14. doi:10.4095/100985.
  18. ^ a b Veevers, J. J. (2004). "Gondwanaland from 650–500 Ma assembly through 320 Ma merger in Pangea to 185–100 Ma breakup: supercontinental tectonics via stratigraphy and radiometric dating". Earth-Science Reviews. 68 (1–2): 1–132. doi:10.1016/j.earscirev.2004.05.002.
  19. ^ a b Sahney, S.; Benton, M.J. (2008). "Recovery from the most profound mass extinction of all time". Proceedings of the Royal Society B: Biological Sciences. 275 (1636): 759–65. doi:10.1098/rspb.2007.1370. PMC 2596898. PMID 18198148.
  20. ^ a b Ware et al. (2015): High-resolution biochronology and diversity dynamics of the Early Triassic ammonoid recovery: the Dienerian faunas of the Northern Indian Margin. Palaeogeography, Palaeoclimatology, Palaeoecology 440:363-373
  21. ^ Schneebeli-Hermann et al. (2015): Vegetation history across the Permian–Triassic boundary in Pakistan (Amb section, Salt Range). Gondwana Research 27:911-924
  22. ^ Hochuli et al. (2016): Severest crisis overlooked—Worst disruption of terrestrial environments postdates the Permian–Triassic mass extinction. Scientific Reports 6:28372
  23. ^ Foster et al. (2020): Suppressed competitive exclusion enabled the proliferation of Permian/Triassic boundary microbialites. The Depositional record 6. 1–13.
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  • Brack, P.; Rieber, H.; Nicora, A. & Mundil, R.; 2005: The Global boundary Stratotype Section and Point (GSSP) of the Ladinian Stage (Middle Triassic) at Bagolino (Southern Alps, Northern Italy) and its implications for the Triassic time scale, Episodes 28(4), pp. 233–244.
  • Gradstein, F. M.; Ogg, J. G. & Smith, A. G.; 2004: A Geologic Time Scale 2004, Cambridge University Press.
  • Kiparisova, Lubov Dmitrievna & Popov, Yurij Nikolaivitch; 1956: Расчленение нижнего отдела триасовой системы на ярусы (Subdivision of the lower series of the Triassic System into stages), Doklady Akademii Nauk SSSR 109(4), pp 842–845 (in Russian).

External linksEdit

Coordinates: 31°04′47″N 119°42′21″E / 31.0797°N 119.7058°E / 31.0797; 119.7058