Avalon assemblage

The Avalon assemblage was the first of the three Late Ediacaran biotic assemblages, spanning from c. 575 Ma to c. 560 Ma. It was followed by the White Sea assemblage, although temporal overlaps have been noted between the biotic assemblages. While earlier macroscopic fossils, mostly of algal origin, are known from the Lantian Formation, Avalon-type localities provide the first evidence of putative metazoan ancestors, as part of the Ediacaran biota.^[1][3][4][5]

Avalon Assemblage
~575 – ~560 Ma[1] PreꞒ Ꞓ O S D C P T J K Pg N
Frondose fossils from Mistaken Point, on the Avalon Peninsula of Canada.
Chronology
−575 — – −570 — – −565 — – −560 — – −555 — – −550 — – −545 — – −540 — – N e o p r o t e r o z o i c P Z Ediacaran Cambrian         Avalon Assemblage White Sea Assemblage Nama Assemblage ← Second pulse of the end-Ediacaran extinction ← ~Baykonurian glaciation ← First pulse of the end-Ediacaran extinction ← Avalon Explosion ← Shuram excursion reaches its peak   Major Glacial period   Shuram excursion[2] Stratigraphic scale of the ICS subdivisions and Ediacaran biotic assmblages Vertical axis scale: millions of years ago
Definition
Type section	Mistaken Point, Newfoundland, Canada 46°37′55″N 53°11′25″W

Research history

The division of the Ediacaran biota in three separate assemblages was first postulated by Ben Waggoner in 2003.^[6]

Geography

Most Avalonian fossil sites are known from the central United Kingdom and eastern Newfoundland, historically connected as part of the Avalonia microcontinent.^[3] Outside of Avalonia proper, other sites have been identified as part of the Avalon assemblage, such as the Olenek Uplift in Siberia, and Sekwi Brooke in the Northwest Territories of Canada.^[7]

Biota

Deep-water rangeomorphs, and to a lesser extent arboreomorphs, dominated the Avalonian biota, although other macrofossil taxa are known. Certain clades typical of the Ediacaran biota, such as dipleurozoans, are not known from Avalon assemblage sites, but only appear in the more recent shallow-water White Sea assemblage.^[3][7] Nonetheless, the Avalon biota has been described as occupying the full range of morphologies that would later be present in the following assemblages.^[1]

References

1. Shen, Bing; Dong, Lin; Xiao, Shuhai; Kowalewski, Michal (4 January 2008). "The Avalon explosion: evolution of Ediacara morphospace". Science. 319 (5859): 81–84. Bibcode:2008Sci...319...81S. doi:10.1126/science.1150279. ISSN 1095-9203. PMID 18174439.
2. Shi, Wei; Li, Chao; Luo, Genming; Huang, Junhua; Algeo, Thomas J.; Jin, Chengsheng; Zhang, Zihu; Cheng, Meng (24 January 2018). "Sulfur isotope evidence for transient marine-shelf oxidation during the Ediacaran Shuram Excursion". Geology. 46 (3): 267–270. doi:10.1130/G39663.1.
3. Liu, Alexander G.; Kenchington, Charlotte G.; Mitchell, Emily G. (June 2015). "Remarkable insights into the paleoecology of the Avalonian Ediacaran macrobiota". Gondwana Research. 27 (4): 1355–1380. Bibcode:2015GondR..27.1355L. doi:10.1016/j.gr.2014.11.002. hdl:1983/ef181134-4023-4747-8137-ed9da7a97771.
4. Bottjer, David J.; Clapham, Matthew E. (2006). Xiao, Shuhai; Kaufman, Alan J. (eds.). Evolutionary Paleoecology of Ediacaran Benthic Marine Animals. Dordrecht: Springer Netherlands. pp. 91–114. doi:10.1007/1-4020-5202-2_4. ISBN 978-1-4020-5202-6.
5. Liu, Alexander G. S. C. (2011). Understanding the Ediacaran Assemblages of Avalonia: A Palaeoenvironmental, Taphonomic and Ontogenetic Study (PhD thesis). University of Oxford. Retrieved 2 April 2024.
6. Waggoner, Ben (1 February 2003). "The Ediacaran Biotas in Space and Time". Integrative and Comparative Biology. 43 (1): 104–113. doi:10.1093/icb/43.1.104. ISSN 1540-7063.
7. Narbonne, Guy M.; Laflamme, Marc; Trusler, Peter W.; Dalrymple, Robert W.; Greentree, Carolyn (March 2014). "Deep-Water Ediacaran Fossils from Northwestern Canada: Taphonomy, Ecology, and Evolution". Journal of Paleontology. 88 (2): 207–223. doi:10.1666/13-053. ISSN 0022-3360.