Shuram excursion
The Shuram excursion, or Shuram-Wonoka excursion, is a change in δ13C, or in the ratio of carbon-13 to carbon-12, taking place during the Ediacaran Period. The exact time period of the excursion is debated among scholars, beginning around 573 Ma and ending around 562{{cite journal |last1=Canfield |first1=Donald Eugene |last2=Knoll |first2=Andrew H. |last3=Poulton |first3=Simon W. |last4=Narbonne |first4=Guy M. |last5=Dunning |first5=Gregory R. |date=February 2020 |title=Carbon isotopes in clastic rocks and the Neoproterozoic carbon cycle |url=https://www.ajsonline.org/content/320/2/97 |journal=American Journal of Science |volume=320 |issue=2 |pages=97–124 |doi=10.2475/02.2020.01 |bibcode=2020AmJS..320...97C |s2cid=214806821 |access-date=12 March 2023}} or 551{{Cite journal |last1=Shi |first1=Wei |last2=Li |first2=Chao |last3=Luo |first3=Genming |last4=Huang |first4=Junhua |last5=Algeo |first5=Thomas J. |last6=Jin |first6=Chengsheng |last7=Zhang |first7=Zihu |last8=Cheng |first8=Meng |date=24 January 2018 |title=Sulfur isotope evidence for transient marine-shelf oxidation during the Ediacaran Shuram Excursion |url=https://pubs.geoscienceworld.org/gsa/geology/article/46/3/267/526708/Sulfur-isotope-evidence-for-transient-marine-shelf |journal=Geology |volume=46 |issue=3 |pages=267–270 |doi=10.1130/G39663.1|bibcode=2018Geo....46..267S }} Ma. It was first noticed in the Wonoka Formation in South Australia in 1990 and later in the Clemente Formation of Mexico in 1992 {{cite journal |journal=Fifth North American Paleontological Convention Abstracts and Program, Paleontological Society Special Publication |last1=McMenamin |first1=M.A.S |last2=Rowland |first2=S.M. |last3=Corsetti |first3=F. |last4=Dix |first4=A.M. |last5=Nance |first5=R.P. |volume=5 |pages=206 |date=1992 |title=Vendian body fossils (?) and isotope stratigraphy from the Caborca area, Sonora, Mexico. |doi=10.1017/S2475262200007668 }} and the Shuram Formation in Oman in 1993.{{cite journal |last1=George Williams and Phillip Schmidt |title=Shuram–Wonoka carbon isotope excursion: Ediacaran revolution in the world ocean's meridional overturning circulation |journal=Geoscience Frontiers |date=March 2018 |volume=9 |issue=2 |pages=391–402 |doi=10.1016/j.gsf.2017.11.006 |bibcode=2018GeoFr...9..391W |doi-access=free }} It is the largest negative δ13C excursion in Earth history, and recovery took 50 million years,{{cite journal |display-authors=etal|last1=Erwan Le Guerroué |title=Chemostratigraphic and sedimentological framework of the largest negative carbon isotopic excursion in Earth history: The Neoproterozoic Shuram Formation (Nafun Group, Oman) |url=https://www.sciencedirect.com/science/article/abs/pii/S0301926806000179 |journal=Precambrian Research |date=20 April 2006 |volume=146 |issue=1–2 |pages=68–92 |doi=10.1016/j.precamres.2006.01.007 |bibcode=2006PreR..146...68L |access-date=12 March 2023}} although the apparent magnitude of the excursion may be distorted due to meteoric water diagenesis.{{Cite journal |last=Cui |first=Huan |date=15 September 2022 |title=Ediacaran Shuram Excursion interpreted, reinterpreted, and misinterpreted: A comment |url=https://linkinghub.elsevier.com/retrieve/pii/S0301926822002704 |journal=Precambrian Research |language=en |volume=380 |pages=106826 |doi=10.1016/j.precamres.2022.106826 |bibcode=2022PreR..38006826C |access-date=18 December 2023 |via=Elsevier Science Direct}}
It is not known what caused the excursion.{{cite journal |last1=Wei |first1=Guang-Yi |last2=Wang |first2=Jiuyuan |last3=Planavsky |first3=Noah J. |last4=Zhao |first4=Mingyu |last5=Bolton |first5=Edward W. |last6=Jiang |first6=Lei |last7=Asael |first7=Dan |last8=Wei |first8=Wei |last9=Ling |first9=Hong-Fei |date=1 July 2022 |title=On the origin of Shuram carbon isotope excursion in South China and its implication for Ediacaran atmospheric oxygen levels |journal=Precambrian Research |volume=375 |page=106673 |doi=10.1016/j.precamres.2022.106673 |bibcode=2022PreR..37506673W |s2cid=248115031 |doi-access=free }} The Shuram excursion may have played a role in sparking the rise of animals that resulted later in the Cambrian explosion.{{cite journal |last1=Colin Barras |title=The weird creatures that might be the very first complex animals|journal=New Scientist |date=Nov 9, 2019 |url=https://www.newscientist.com/article/mg24432550-700-the-weird-creatures-that-might-be-the-very-first-complex-animals/}} The oxygen-consuming Ediacara biota experienced a radiation during the isotopic excursion as a response to the transient surplus of oxidants.{{cite journal |last1=Shields |first1=Graham A. |last2=Mills |first2=Benjamin J. W. |last3=Zhu |first3=Maoyan |last4=Raub |first4=Timothy D. |last5=Daines |first5=Stuart J. |last6=Lenton |first6=Timothy M. |date=2 September 2019 |title=Unique Neoproterozoic carbon isotope excursions sustained by coupled evaporite dissolution and pyrite burial |url=https://www.nature.com/articles/s41561-019-0434-3?error=cookies_not_supported&code=5b84f102-268e-4f63-8332-ea92a0ee76ea |journal=Nature Geoscience |volume=12 |issue=10 |pages=823–827 |doi=10.1038/s41561-019-0434-3 |bibcode=2019NatGe..12..823S |hdl=10871/39006 |s2cid=201827639 |access-date=12 January 2023|hdl-access=free }} Microbial blooms of oxygenic phototrophs regulated the recovery of the carbon cycle from the isotopic excursion.{{cite journal |last1=Cañadas |first1=Fuencisla |last2=Papineau |first2=Dominic |last3=Leng |first3=Melanie J. |last4=Li |first4=Chao |date=10 January 2022 |title=Extensive primary production promoted the recovery of the Ediacaran Shuram excursion |journal=Nature Communications |volume=13 |issue=1 |page=148 |doi=10.1038/s41467-021-27812-5 |pmid=35013337 |pmc=8748710 |bibcode=2022NatCo..13..148C }}