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TitleThe Smithian/Spathian boundary (late Early Triassic): a review of ammonoid, conodont, and carbon-isotopic criteria
AuthorZhang, L; Orchard, M JORCID logo; Brayard, AORCID logo; Algeo, T JORCID logo; Zhao, L S; Chen, Z Q; Lyu, Z Y
SourceEarth-Science Reviews vol. 195, 2019 p. 7-36, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20200184
Mediapaper; on-line; digital
File formatpdf
ProvinceOffshore region
Lat/Long WENS-180.0000 180.0000 90.0000 -90.0000
Subjectsgeochronology; Nature and Environment; Science and Technology; stratigraphy; Lower Triassic; Smithian; Spathian; carbon isotopes; thermal analyses; biostratigraphy; conodonts; Boreale Zone; Tethyan; Triassic
Illustrationsgeochronological charts; stratigraphic columns; stratigraphic charts; location maps; stratigraphic sections; photographs
Released2019 02 15
AbstractThe transition from the Smithian substage to the Spathian substage of the Olenekian stage of the late Early Triassic was a critical time marked by a series of biological and environmental changes during the multimillion-year recovery interval following the end-Permian mass extinction. However, the Smithian/Spathian boundary (SSB) does not yet have an agreed definition, a shortcoming that complicates high-resolution analysis of events during the Smithian-Spathian transition. Here, we review key biostratigraphic (i.e., ammonoid and conodont) studies of the Smithian and Spathian substages in historically important regions (e.g., the Canadian Arctic for the Boreal realm, western North America for the eastern Panthalassic Ocean) and more recently re-studied locations (e.g., Pakistan and India in the southern Tethys, South China in the eastern Tethys) as well as the carbon isotope chemostratigraphy of 29 major Smithian-Spathian sections globally. Key ammonoid genera (e.g., Wasatchites, Anasibirites, Glyptophiceras and Xenoceltites of the late Smithian, and Bajarunia, Tirolites and Columbites of the early Spathian), conodont species (e.g., Scythogondolella milleri, Novispathodus waageni, and Borinella buurensis of the late Smithian, and Triassospathodus' hungaricus, Neogondolella aff. sweeti, and Icriospathodus spp. of the early Spathian), and carbonate carbon isotope excursions provide appropriate markers for constraining the SSB. Use of the first occurrence of the conodont Novispathodus pingdingshanensis as a potential marker of the SSB is also discussed. Based on correlations of biostratigraphic and carbon isotope data globally, we propose to revise previous placements of the SSB transition in some sections. Finally, we show that the Smithian Thermal Maximum (STM; herein named) was middle Smithian in age and not correlative with the SSB, as inferred in some earlier studies, and that the SSB coincided with a subsequent major global cooling event.

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