Trilobite zone
index fossils to subdivide the Cambrian period
Trilobites are used as index fossils to subdivide the Cambrian period. Assemblages of trilobites define trilobite zones. The Olenellus-zone has traditionally marked the top of the Lower Cambrian, and is followed by the Eokochaspis zone.
The last two zones of the Middle Cambrian are the Bathyuriscus–Elrathina-zone (contemporaneous with the Burgess Shale) and the subsequent Bolaspidella-zone (starting at the base of the Drumian stage). These are overlain by the lowermost Upper Cambrian Cedaria-zone.
Alternative zoning names place the Burgess Shale in the Peronopsis bonnerensis-zone, which is underlain by the Oryctocephalus indicus-zone (e.g. Spence Shale) and overlain (perhaps not directly) by the Ptychagnostus punctuosus-zone.
The lower Middle Cambrian Glossopleura-zone (Spence Shale) is above the Albertella-zone.
The Elvinia-zone is upper Cambrian.
Subdivision of the Olenellus-zone
Recently, it has been proposed to subdivide the Olenellus-zone.
The public source identifies “Trilobite zone” as index fossils to subdivide the Cambrian period. This brief keeps that definition visible, then builds a research path around Trilobite, zone and index.
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This entry incorporates text from “Trilobite zone” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.