Trilobite zone#Subdivision of the Olenellus-zone
{{Short description|Index fossils to subdivide the Cambrian period}}
{{Update|article|inaccurate=y|date=November 2012}}
Trilobites are used as index fossils to subdivide the Cambrian period. Assemblages of trilobites define trilobite zones.{{Cite journal|last= Palmer|first= A.R.|year= 1998|title= A proposed nomenclature for stages and series for the Cambrian of Laurentia|journal= Canadian Journal of Earth Sciences|volume= 35|issue= 4|pages= 323–328|url= http://article.pubs.nrc-cnrc.gc.ca/ppv/RPViewDoc?issn=1480-3313&volume=35&issue=4&startPage=323|issn= 1480-3313|bibcode = 1998CaJES..35..323P |doi= 10.1139/cjes-35-4-323 }} The Olenellus-zone has traditionally marked the top of the Lower Cambrian,{{Cite journal| doi =10.1666/0022-3360(2005)079<0063:TTSANL>2.0.CO;2| jstor = 4094961| pages = 63–71| title = The Topazan Stage, a New Laurentian Stage (Lincolnian Series_ "Middle" Cambrian)| last1 =Sundberg| journal = Journal of Paleontology| volume = 79| issue = 1| publisher = Paleontological Society| year = 2005 | first1 = F. A.| s2cid = 130681546}} and is followed by the Eokochaspis zone.{{Cite journal| doi =10.1666/0022-3360(2000)074<0604:PTOTLM>2.0.CO;2| jstor = 1306942| pages = 604–630| title = Ptychopariid Trilobites of the Lower-Middle Cambrian Boundary Interval, Pioche Shale, Southeastern Nevada| last1 =Sundberg| journal = Journal of Paleontology| volume = 74| issue = 4| publisher = Paleontological Society| year = 2000 | first1 = F. A.| last2 =McCollum | first2 = L. B.| s2cid = 130102939}}
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{{Cite web | url=https://engineering.purdue.edu/Stratigraphy/references/Drumian0.pdf | title=The Global boundary Stratotype Section and Point (GSSP) of the Drumian Stage (Cambrian) in the Drum Mountains, Utah, USA | access-date=2024-07-24 | website=engineering.purdue.edu | first1=Loren E. | last1=Babcock | first2=Richard A. | last2=Robison | first3=Margaret N. | last3=Rees | first4=Shanchi | last4=Peng | first5=Matthew R. | last5=Saltzman}}). These are overlain by the lowermost Upper Cambrian Cedaria-zone.{{Cite journal| last1 = Robison | first1 = R. A.| title = Upper Middle Cambrian Stratigraphy of Western Utah| journal = Geological Society of America Bulletin| volume = 75| issue = 10| pages = 995–1010| year = 1964| issn = 0016-7606| doi = 10.1130/0016-7606(1964)75[995:UMCSOW]2.0.CO;2| bibcode = 1964GSAB...75..995R}}
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{{Cite journal| last1 = Robison | first1 = R. A.| last2 = Wiley | first2 = E. O.| title = A New Arthropod, Meristosoma: More Fallout from the Cambrian Explosion| jstor = 1306320| journal = Journal of Paleontology| volume = 69| issue = 3| pages = 447–459| year = 1995| doi = 10.1017/s0022336000034855| bibcode = 1995JPal...69..447R| s2cid = 133177339}} Glossopleura-zone (Spence Shale) is above the Albertella-zone.{{Cite journal| last1 = Stoyanow | first1 = A.| title = Sonoraspis and Albertella in the Inyo Mountains, California| journal = Geological Society of America Bulletin| volume = 69| issue = 3| pages = 347–352| year = 1958| issn = 0016-7606| doi = 10.1130/0016-7606(1958)69[347:SAAITI]2.0.CO;2| bibcode = 1958GSAB...69..347S}}
The Elvinia-zone is upper Cambrian.{{Cite journal| last1 = Stitt | first1 = J. H.| last2 = Rucker | first2 = J. D.| last3 = Diane Boyer | first3 = N.| last4 = Hart | first4 = W. D.| title = New Elvinia Zone (Upper Cambrian) Trilobites from New Localities in the Collier Shale, Ouachita Mountains, Arkansas| jstor = 1306200| journal = Journal of Paleontology| volume = 68| issue = 3| pages = 518–523| year = 1994| doi = 10.1017/s0022336000025890| bibcode = 1994JPal...68..518S| s2cid = 133418468}}
| class="wikitable" style="text-align:center;" | |||
| Series | Stage | Trilobite zone | Trilobite GSSP |
|---|---|---|---|
| rowspan=4 style="background-color:{{period color|Furongian}};" | Furongian | style="background-color:{{period color|Stage 10}};" |Stage 10 | Saukia-zone (upper part), Eurekia apopsis-zone, Tangshanaspis-Zone, Parakoldinioidia-zone, Symphysurina-zone{{cite journal|last= Landing|first= E. |author2=Westrop, S.R. |author3=Adrain, J.M.|title= The Lawsonian Stage - the Eoconodontus notchpeakensis FAD and HERB carbon isotope excursion define a globally correlatable terminal Cambrian stage|journal= Bulletin of Geosciences|date= 19 September 2011|pages= 621–640|doi= 10.3140/bull.geosci.1251|doi-access= free}} | Lotagnostus americanus (undecided) |
| style="background-color:{{period color|stage 9}};" | Jiangshanian | Ellipsocephaloides-zone, Saukia-zone (lower part) | Agnostotes orientalis | |
| rowspan=2 style="background-color:{{period color|Paibian}};" | Paibian | ? (?) | rowspan=2 | Glyptagnostus reticulatus | |
| | Cedaria | |||
| rowspan=4 style="background-color:{{period color|Miaolingian}};" | Miaolingian | style="background-color:{{period color|guzhangian}};" | Guzhangian
| rowspan=2 | Bolaspidella ( / Ptychagnostus praecurrens ?? ).This is just younger than the Bathyuriscus-Elrathina zone, or at least just younger than the Stephen Formation. See
| Lejopyge laevigata | |
| style="background-color:{{period color|drumian}};" | Drumian | Ptychagnostus atavus | ||
| rowspan=2 style="background-color:{{period color|Wuliuan}};" | Wuliuan | Bathyuriscus–Elrathina (?) | rowspan=2 | Oryctocephalus indicus | |
| Eokochaspis | |||
| rowspan=3 style="background-color:{{period color|Series 2}};" | Series 2 | style="background-color:{{period color|stage 4}};" | Stage 4 | rowspan = 2 | Olenellus | Olenellus or Redlichia (undecided) |
| rowspan=2 style="background-color:{{period color|stage 3}};" | Stage 3 | |||
| Fallotaspis, Nevadella | First appearance of trilobites (undecided) | ||
| rowspan=2 style="background-color:{{period color|Series 1}};" |Terreneuvian (Pre-Trilobitic Cambrian) | style="background-color:{{period color|stage 2}};" | Stage 2 | ? | |
| style="background-color:{{period color|stage 1}};" | Fortunian
| |
Subdivision of the ''Olenellus''-zone
Recently, it has been proposed to subdivide the Olenellus-zone.{{cite journal|first= Mark|last= Webster|title= Trilobite Biostratigraphy and Sequence Stratigraphy of the Upper Dyeran (traditional Laurentian "Lower Cambrian) in the southern Great Basis, USA|year= 2011|journal=Museum of Northern Arizona Bulletin|volume= 67}} 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),
Olenellus puertoblancoensis s.l.,
Olenellus fowleri s.l.,
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 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
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