Cambrian Stage 3

Cambrian Stage 3 is the still unnamed third stage of the Cambrian. It succeeds Cambrian Stage 2 and precedes Cambrian Stage 4, although neither its base nor top have been formally defined. The plan is for its lower boundary to correspond approximately to the first appearance of trilobites, about 521 million years ago,^[2] though the globally asynchronous appearance of trilobites warrants the use of a separate, globally synchronous marker to define the base.^[3] The upper boundary and beginning of Cambrian Stage 4 is informally defined as the first appearance of the trilobite genera Olenellus or Redlichia around 514.5 million years ago.^[4]

Cambrian Stage 3
~521 – ~514.5 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Chronology
−540 — – −535 — – −530 — – −525 — – −520 — – −515 — – −510 — – −505 — – −500 — – −495 — – −490 — – −485 — N ♇ P a l e o z o i c Ediacaran C a m b r i a n O T e r r e n e u v i a n S e r i e s 2 M i a o l i n g. F u r o n g. E Fortunian "Stage 2" "Stage 3" "Stage 4" Wuliuan Drumian Guzhangian Paibian Jiangshanian "Stage 10" Tremadocian               ← Orsten Fauna ← Burgess Shale ← Kaili biota ← Archaeocyatha extinction ← Emu Bay Shale ← Sirius Passet biota ← Chengjiang biota ← First Trilobites ← SSF diversification, first brachiopods & archaeocyatha ← First halkieriids, mollusсs, hyoliths SSF ← Baykonurian glaciation ← Dresbachian extinction   Major Glacial period Subdivision of the Cambrian according to the ICS, as of 2024.[1] Vertical axis scale: Millions of years ago
Etymology
Name formality	Informal
Usage information
Celestial body	Earth
Regional usage	Global (ICS)
Time scale(s) used	ICS Time Scale
Definition
Chronological unit	Age
Stratigraphic unit	Stage
Time span formality	Formal
Lower boundary definition	Not formally defined
Lower boundary definition candidates	FAD of Trilobites
Lower boundary GSSP candidate section(s)	None
Upper boundary definition	Not formally defined
Upper boundary definition candidates	FAD of the Trilobites Olenellus or Redlichia
Upper boundary GSSP candidate section(s)	None

Naming

The International Commission on Stratigraphy has not officially named the 3rd stage of the Cambrian. The stage approximately corresponds to the "Atdabanian", which is used by geologists working in Siberia.^[5]

Biostratigraphy

The oldest trilobite known is Lemdadella which appears at the beginning of the Fallotaspis zone.^[6] The Cambrian radiation of animal phyla ends here, after the diversification and origination of arthropods, molluscs, lophophorates, chordates (including vertebrates) among others.^[7]