Graptolite succession across the Ordovician–Silurian boundary in south-eastern Alaska

Michael Churkin; Claire Carter; George Donald Eberlein

doi:10.1144/gsjgs.126.1.0319

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Graptolite succession across the Ordovician–Silurian boundary in south-eastern Alaska

Michael Churkin·Claire Carter·George Donald Eberlein

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Abstract

The first discovery in North America of a succession of graptolite faunas across the Ordovician–Silurian boundary has been made on Esquibel Island, in south-eastern Alaska, where five graptolite zones are represented in an 18 m interval of shale in the Descon Formation. Despite the thinness of the graptolite zones, no stratigraphical breaks can be inferred from more complete graptolite successions known elsewhere. The Alaskan faunas can be closely correlated with those of the standard British zones—the Dicellograptus anceps Zone (uppermost Ordovician), the Glyptograptus persculptus Zone (lowermost Silurian) and the immediately overlying Akidograptus acuminatus, Orthograptus vesiculosus and Monograptus cyphus Zones of the Lower Silurian. They thus give evidence of the cosmopolitan distribution of graptolite faunas during latest Ordovician and earliest Silurian time.

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Source-reported bounding extent: 55.61539513584262° to 55.65454133850121° latitude; -133.60301971435547° to -133.54362487792966° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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Michael Churkin, Claire Carter, George Donald Eberlein. 2022-04-05. Graptolite succession across the Ordovician–Silurian boundary in south-eastern Alaska. https://doi.org/10.1144/gsjgs.126.1.0319

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