Trilobite zone

Short description: Index fossils to subdivide the Cambrian period

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Trilobites are used as index fossils to subdivide the Cambrian period. Assemblages of trilobites define trilobite zones.[1] The Olenellus-zone has traditionally marked the top of the Lower Cambrian,[2] and is followed by the Eokochaspis zone.[3]

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[4]). These are overlain by the lowermost Upper Cambrian Cedaria-zone.[5]

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.[6]

The lower Middle Cambrian[7] Glossopleura-zone (Spence Shale) is above the Albertella-zone.[8]

The Elvinia-zone is upper Cambrian.[9]

Series | Stage | Trilobite zone | Trilobite GSSP

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Furongian | Stage 10 | Saukia-zone (upper part), Eurekia apopsis-zone, Tangshanaspis-Zone, Parakoldinioidia-zone, Symphysurina-zone[10] | Lotagnostus americanus (undecided)
Jiangshanian | Ellipsocephaloides-zone, Saukia-zone (lower part) [10] | Agnostotes orientalis
Paibian | ? (?) | Glyptagnostus reticulatus
Cedaria
Miaolingian | Guzhangian | Bolaspidella ( / Ptychagnostus praecurrens ?? ).[6] | Lejopyge laevigata
Drumian | Ptychagnostus atavus
Wuliuan | Bathyuriscus-Elrathina (?) | Oryctocephalus indicus
Eokochaspis
Series 2 | Stage 4 | Olenellus | Olenellus or Redlichia (undecided)
Stage 3
Fallotaspis, Nevadella | First appearance of trilobites (undecided)
Terreneuvian (Pre-Trilobitic Cambrian) | Stage 2 | ?
Fortunian |

## Subdivision of the Olenellus-zone

Recently, it has been proposed to subdivide the Olenellus-zone.[11] The following zones have been proposed to replace the Upper Olenellus-zone. Each lower boundary is defined by the first occurrence of the naming species. Each upper boundary is defined by the first occurrence of the naming species of the overlying zone. In case of the youngest zone, this is Eokochaspis nodosa, that also marks the base of the Wuliuan.

* Nephrolenellus multinodus-zone (youngest).

Species: Nephrolenellus multinodus (lower half), Mesonacis fremonti, Olenellus terminatus s.l., Olenellus puertoblancoensis s.l., Olenellus fowleri s.l., Olenellus gilberti, Bolbolenellus brevispinus (not the lower part), Olenellus chiefensis (upper half), Olenellus sp.1 (upper half), Nephrolenellus geniculatus (upper part), Olenellus sp.2 (upper part), Olenellus howelli (very uppermost part).

* Bolbolenellus euryparia-zone.

Species: Bolbolenellus euryparia (lower half), Mesonacis fremonti, Bristolia fragilis s.l. (lower half), Olenellus terminatus s.l., Olenellus fowleri s.l., Olenellus puertoblancoensis s.l., Olenellus gilberti (uppermost part), Biceratops nevadensis (uppermost part), Bristolia brachyomma (very uppermost part).

* Peachella iddingsi-zone.

Species: Peachella iddingsi (lower half), Mesonacis fremonti, Olenellus nevadensis (lower part), Bristolia anteros (lowest half), Bristolia fragilis s.l., Olenellus terminatus s.l., Paranephrolenellus besti (very short period in the late lower part), Peachella brevispina (middle part).

* Bristolia insolens-zone.

Species: Bristolia insolens (lower half), Mesonacis fremonti, Olenellus nevadensis, Olenellus clarki, Olenellus sp.3, Paranephrolenellus klondykensis (lowest part), Bristolia harringtoni (middle part), Bristolia bristolensis (lower half), Bristolia anteros (not lowest part), Bristolia fragilis s.l. (upper half), Paranephrolenellus inflatus (very short interval in the middle), Eopeachella angustispina (uppermost part).

* Bristolia mohavensis-zone.

Species: Bristolia mohavensis (lower half), Mesonacis fremonti, Olenellus nevadensis, Olenellus clarki, Olenellus sp.3, Bristolia harringtoni (middle part), Bristolia bristolensis (upper half).

* Arcuolenellus arcuatus-zone (oldest).

Species: Arcuolenellus arcuatus (lowest part), Arcuolenellus aff. megafrontatis (lower half), Mesonacis cylindricus (not the highest part), Olenellus nevadensis, Olenellus clarki (not lowest part), Mesonacis fremonti (upper half), Olenellus sp.3 (upper part).

## References

1. ↑ Palmer, A.R. (1998). "A proposed nomenclature for stages and series for the Cambrian of Laurentia". Canadian Journal of Earth Sciences 35 (4): 323–328. doi:10.1139/cjes-35-4-323. ISSN 1480-3313. Bibcode: 1998CaJES..35..323P. http://article.pubs.nrc-cnrc.gc.ca/ppv/RPViewDoc?issn=1480-3313&volume=35&issue=4&startPage=323.
2. ↑ Sundberg, F. A. (2005). "The Topazan Stage, a New Laurentian Stage (Lincolnian Series_ "Middle" Cambrian)". Journal of Paleontology (Paleontological Society) 79 (1): 63–71. doi:10.1666/0022-3360(2005)079<0063:TTSANL>2.0.CO;2.2.0.CO;2&rfr_id=info:sid/en.wikibooks.org:Earth:Trilobite_zone">
3. ↑ Sundberg, F. A.; McCollum, L. B. (2000). "Ptychopariid Trilobites of the Lower-Middle Cambrian Boundary Interval, Pioche Shale, Southeastern Nevada". Journal of Paleontology (Paleontological Society) 74 (4): 604–630. doi:10.1666/0022-3360(2000)074<0604:PTOTLM>2.0.CO;2.
4. ↑ Babcock, Loren E.; Robison, Richard A.; Rees, Margaret N.; Peng, Shanchi; Saltzman, Matthew R.. "The Global boundary Stratotype Section and Point (GSSP) of the Drumian Stage (Cambrian) in the Drum Mountains, Utah, USA". https://engineering.purdue.edu/Stratigraphy/references/Drumian0.pdf.
5. ↑ Robison, R. A. (1964). "Upper Middle Cambrian Stratigraphy of Western Utah". Geological Society of America Bulletin 75 (10): 995–1010. doi:10.1130/0016-7606(1964)75[995:UMCSOW2.0.CO;2]. ISSN 0016-7606. Bibcode: 1964GSAB...75..995R.
6. ↑ 6.0 6.1 This is just younger than the Bathyuriscus-Elrathina zone, or at least just younger than the Stephen Formation. See
* Conway Morris, S.; Robison, R. A. (1986). "Middle Cambrian priapulids and other soft-bodied fossils from Utah and Spain". University of Kansas Paleontological Contributions 117: 1–22. http://kuscholarworks.ku.edu/dspace/bitstream/1808/3696/1/paleo.paper.117.pdf.
7. ↑ Robison, R. A.; Wiley, E. O. (1995). "A New Arthropod, Meristosoma: More Fallout from the Cambrian Explosion". Journal of Paleontology 69 (3): 447–459. doi:10.1017/s0022336000034855. Bibcode: 1995JPal...69..447R.
8. ↑ Stoyanow, A. (1958). "Sonoraspis and Albertella in the Inyo Mountains, California". Geological Society of America Bulletin 69 (3): 347–352. doi:10.1130/0016-7606(1958)69[347:SAAITI2.0.CO;2]. ISSN 0016-7606. Bibcode: 1958GSAB...69..347S.
9. ↑ Stitt, J. H.; Rucker, J. D.; Diane Boyer, N.; Hart, W. D. (1994). "New Elvinia Zone (Upper Cambrian) Trilobites from New Localities in the Collier Shale, Ouachita Mountains, Arkansas". Journal of Paleontology 68 (3): 518–523. doi:10.1017/s0022336000025890. Bibcode: 1994JPal...68..518S.
10. ↑ 10.0 10.1 Landing, E.; Westrop, S.R.; Adrain, J.M. (19 September 2011). "The Lawsonian Stage - the Eoconodontus notchpeakensis FAD and HERB carbon isotope excursion define a globally correlatable terminal Cambrian stage". Bulletin of Geosciences: 621–640. doi:10.3140/bull.geosci.1251.
11. ↑ Webster, Mark (2011). "Trilobite Biostratigraphy and Sequence Stratigraphy of the Upper Dyeran (traditional Laurentian "Lower Cambrian) in the southern Great Basis, USA". Museum of Northern Arizona Bulletin 67.

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