Journal article
Trilobite biostratigraphy and revised bases of the Tulean and Blackhillsian Stages of the Ibexian Series, Lower Ordovician, Western United States
Memoir ... of the Association of Australasian Palaeontologists, Vol.37, pp.541-610
2009
Abstract
Extensive new field collections and taxonomic work permit the development of a much higher resolution trilobite biostratigraphy for the Lower Ordovician Tulean and Blackhillsian stages of western Laurentia than has previously been possible. The five zones used previously are replaced by 15 formally designated zones, of which one is unaltered from the previous scheme, three are restricted with new boundary definitions, and 11 are newly proposed. The uppermost part of the Blackhillsian Stage has not been studied and may contain additional undescribed diversity. The base of the Tulean Stage is revised downward to the base of the (new) Litzicurus shawi Zone, which corresponds to an episode of abrupt trilobite faunal turnover in the form of a 'biomere'-style mass extinction and the coordinated first appearance of multiple trilobite genera characteristic of the remainder of the Tulean. A new boundary stratotype for this base is designated at Section HC6 142.0 m in the Garden City Formation of southeastern Idaho. As recognised by previous workers, the correlative interval in the type section of the Tulean Stage in western Utah is poorly fossiliferous and the position of the turnover event cannot be located, only inferred. The base of the Blackhillsian Stage has been defined as the base of the Trigonocerca typica Zone by previous authors. This zone is abandoned due to misidentification of the name bearer in the stratotype and the fact that the true first appearance of this species can now be shown to occur within a stratigraphic interval characterised by an otherwise uniform trilobite fauna. The Blackhillsian Stage is revised with a base coinciding with the base of the new Strigigenalis plicolabeona Zone, and the boundary stratotype is now a few metres higher in the same section as the original. The new zonal scheme in ascending order includes the Tulean Litzicurus shawi Zone (new), Psalikilus spinosum Zone (new), Hintzeia celsaora Zone (restricted), Psalikilopsis cuspicaudata Zone (new), Psalikilus typicum Zone (new), Psalikilus hestoni Zone (new), Protopliomerella contracta Zone (restricted), Heckethornia hyndeae Zone (new), Heckethornia bowiei Zone (new), Psalikilus pikum Zone (new), and the Blackhillsian Strigigenalis plicolabeona Zone (new), Carolinites nevadensis Zone (new), Presbynileus ibexensis Zone, Pseudocybele paranasuta Zone (new), an interval presently referred to the 'Pseudocybele nasuta Zone' (restricted), and an unsampled overlying interval in the highest Blackhillsian. Two of the name bearers of the new zones, Litzicurus shawi gen. et sp. nov. and Psalikilus hestoni sp. nov. are formally described.
Details
- Title: Subtitle
- Trilobite biostratigraphy and revised bases of the Tulean and Blackhillsian Stages of the Ibexian Series, Lower Ordovician, Western United States
- Creators
- Jonathan M Adrain - University of IowaNeo E. B McAdamsStephen R Westrop
- Contributors
- J. R Laurie (Editor)G. A Brock (Editor)John R Paterson (Editor)
- Resource Type
- Journal article
- Publication Details
- Memoir ... of the Association of Australasian Palaeontologists, Vol.37, pp.541-610
- Publisher
- Association of Australasian Palaeontologists
- ISSN
- 0810-8889
- Alternative title
- Cambro-Ordovician studies III
- Language
- English
- Date published
- 2009
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984240887302771
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