The Shuram excursion, or Shuram-Wonoka excursion, is a change in
δ13C, or in the ratio of
carbon-13
Carbon-13 (13C) is a natural, stable isotope of carbon with a nucleus containing six protons and seven neutrons. As one of the environmental isotopes, it makes up about 1.1% of all natural carbon on Earth.
Detection by mass spectrometry
A mass ...
to
carbon-12
Carbon-12 (12C) is the most abundant of the two stable isotopes of carbon (carbon-13 being the other), amounting to 98.93% of element carbon on Earth; its abundance is due to the triple-alpha process by which it is created in stars. Carbon-12 i ...
, taking place between around 573 and 562 million years ago, during the
Ediacaran Period
The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and th ...
. It was first noticed in the Wonoka Formation in
South Australia
South Australia (commonly abbreviated as SA) is a state in the southern central part of Australia. It covers some of the most arid parts of the country. With a total land area of , it is the fourth-largest of Australia's states and territories ...
in 1990 and later in the Shuram Formation in Oman in 1993. It is the largest negative δ
13C excursion in Earth history, and recovery took 50 million years, although the apparent magnitude of the excursion may be distorted due to meteoric water diagenesis.
It is not known what caused the excursion. The Shuram excursion may have played a role in sparking the rise of animals that resulted later in the
Cambrian explosion
The Cambrian explosion, Cambrian radiation, Cambrian diversification, or the Biological Big Bang refers to an interval of time approximately in the Cambrian Period when practically all major animal phyla started appearing in the fossil recor ...
. The oxygen-consuming
Ediacara biota
The Ediacaran (; formerly Vendian) biota is a taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period (). These were composed of enigmatic tubular and frond-shaped, mostly sessi ...
experienced a radiation during the isotopic excursion as a response to the transient surplus of oxidants.
Microbial blooms of oxygenic phototrophs regulated the recovery of the carbon cycle from the isotopic excursion.
References
{{Reflist
Ediacaran