Journal article
The Lawsonian stage- the Eoconodontus notchpeakensis(miller, 1969) FAD and HERB carbon isotope excursion define a globally correlatable terminal Cambrian stage
Bulletin of geosciences, Vol.86(3), pp.621-640
2011
DOI: 10.3140/bull.geosci.1251
Abstract
The best definition for the base of the terminal Cambrian (Stage 10) is the conodont Eoconodontus notchpeakensis FAD ± onset of the HERB carbon isotope excursion. These horizons allow precise intercontinental correlations in deep marine to peritidal facies. The agnostoid Lotagnostus americanus (Billings, 1860) FAD has been suggested as a Stage 10 base, but restudy of types and typotypes shows that the species occurs only in Late Cambrian (Sunwaptan) debris flow boulders in Quebec (Westrop et al. , this volume). Non-Quebec reports of " L. americanus " are an amalgum of small samples of often poorly documented specimens with effaced–highly furrowed cephala and pygidia and with or without a highly trisected pygidial posteroaxis. Many of these occurrences have local species names, but no evidence suggests that they record intraspecific variation of a globally distributed taxon. They are not synonyms of L . americanus . Lotagnostus , largely a dysoxic form, does not allow precise correlation into oxygenated platform facies. Another proposal used the conodont Cordylodus andresi FAD as a Stage 10 base, but other work shows this FAD is diachronous. An unrealistic approach to L. americanus ’ systematics and the correlation uncertainty of C. andresi are overcome by defining a Stage 10 base at the globally recognizable E. notchpeakensis FAD, with the C. andresi FAD a useful proxy on cool-water continents. The "Lawsonian Stage", named for Lawson Cove in western Utah, has a basal GSSP at the E. notchpeakensis FAD and replaces informal Stage 10. The Lawsonian, ~150 m-thick in western Utah, underlies the basal Ordovician Iapetognathus Zone.
Details
- Title: Subtitle
- The Lawsonian stage- the Eoconodontus notchpeakensis(miller, 1969) FAD and HERB carbon isotope excursion define a globally correlatable terminal Cambrian stage
- Creators
- Ed LandingStephen R WestropJonathan M Adrain
- Resource Type
- Journal article
- Publication Details
- Bulletin of geosciences, Vol.86(3), pp.621-640
- DOI
- 10.3140/bull.geosci.1251
- ISSN
- 1214-1119
- eISSN
- 1802-8225
- Language
- English
- Date published
- 2011
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9983983653302771
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