Geographical extension

Geographical repartition of Archaeocyathan is a world-wide scale. They are present on every continent:

• Africa: Morocco, South Africa
• Antarctica
• Asia: China, Kazakhstan, Ouzbekistan, Mongolia, Russia
• Europe: France, Germany, Poland, Sardinia, Serbia, Spain
• North America: Canada, Greenland, USA
• Mexico
• Oceania: Australia
• South America: Argentina, Falklands Islands

Enlarge map

Figure 4: geographical repartition of archaeocyaths.
In Russia, only area with a lot of fossiliferous towns are mentionned. (A.KERNER)

Stratigraphical extension

Archaeocyathan appear during the Tommotian stage on the Siberian Platform. They conquered intertropical zones by successive migrations that followed the transgressions which are responsible of carbonate buildups formation. Their extension and diversity apogee is reached during the lower and middle Botoman.
From Botoman end, important environnemental changes happened:

• A major regression which means a carbonate builsups decrease.
• An anoxic episode (water without any 02).
• Continental drift: continental blocks move to highest latitudes (there are less shalow seas between the tropics).

These changes mean a progressive nearly total extinction of archaeocyathan at the end of the Toyonian (End of the Lower Cambrian). During the Middle Cambrian just two genera are present and only one during the Upper Cambrian in Antarctica (just this block was between the tropics yet).
They disapear at cambrian-ordovician time line.

Biostratigraphy

The first stage subdivision based on archaeocyaths was established on Siberian platform (Zhuravleva, 1960). Archaeocyathan biozones has been established in key Cambrian section in Siberia, Morocco, Spain, Canada and Australia allowing stratigraphical comparisons in parallel or in substitution to trilobites biozones.

Paleoecology

Archaeocyaths are sessile, benthic and filter feeder organisms. They live exclusively on carbonate buildups situated between the tropics. They are able to live only in restricted environnemental conditions:

• of temperature (stenothermal: tolerate only a narrow temperature range)
• of salinity (stenohaline: tolerate only a narrow range of salinity)
• of depth (stenobathic: can live within only a small range of depth => intertidal zone to subtidal zone)

Since the Cambrian system is generally characterized by a lack of any climate indicators, archaeocyathan are one of the best indicators for environmental and ecological reconstruction (Debrenne et al. 2002)(Gandin & Debrenne 2010)

Paleobiogeography

Maps reconstructions are quite difficult for Precambrian/Cambrian due to paleomagnetism problems and a lack of any usual climate indicators. Archaeocyathan live exclusively on carbonate buildups situated between the tropics (30°N, 30°S). Their occurrence is helpful for paleogeographical reconstructions and for constraints tectonic ones.