Trilobite zone


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 and the subsequent Bolaspidella-zone. 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 and overlain by the Ptychagnostus punctuosus-zone.
The lower Middle Cambrian Glossopleura-zone 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 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.
Species:
Nephrolenellus multinodus,
Mesonacis fremonti,
Olenellus terminatus s.l.,
Olenellus puertoblancoensis s.l.,
Olenellus fowleri s.l.,
Olenellus gilberti,
Bolbolenellus brevispinus,
Olenellus chiefensis,
Olenellus sp.1,
Nephrolenellus geniculatus,
Olenellus sp.2,
Olenellus howelli.
Species: Bolbolenellus euryparia,
Mesonacis fremonti,
Bristolia fragilis s.l.,
Olenellus terminatus s.l.,
Olenellus fowleri s.l.,
Olenellus puertoblancoensis s.l.,
Olenellus gilberti,
Biceratops nevadensis,
Bristolia brachyomma.
Species: Peachella iddingsi,
Mesonacis fremonti,
Olenellus nevadensis,
Bristolia anteros,
Bristolia fragilis s.l.,
Olenellus terminatus s.l.,
Paranephrolenellus besti,
Peachella brevispina.
Species: Bristolia insolens,
Mesonacis fremonti,
Olenellus nevadensis,
Olenellus clarki,
Olenellus sp.3,
Paranephrolenellus klondykensis,
Bristolia harringtoni,
Bristolia bristolensis,
Bristolia anteros,
Bristolia fragilis s.l.,
Paranephrolenellus inflatus,
Eopeachella angustispina.
Species: Bristolia mohavensis,
Mesonacis fremonti,
Olenellus nevadensis,
Olenellus clarki,
Olenellus sp.3,
Bristolia harringtoni,
Bristolia bristolensis.
Species: Arcuolenellus arcuatus,
Arcuolenellus aff. megafrontatis,
Mesonacis cylindricus,
Olenellus nevadensis,
Olenellus clarki,
Mesonacis fremonti,
Olenellus sp.3''.