Iona Group

Last updated
Iona Group
Stratigraphic range: 1000–950 Ma
Type Group
Unit of Wester Ross Supergroup
Thickness~700 m
Lithology
Primarymetasandstone
Othermetasiltstone, semipelite, mylonite, conglomerate
Location
Region Inner Hebrides
Country Scotland
Type section
Named for Iona

The Iona Group is a sequence of metamorphosed Neoproterozoic sedimentary rocks that outcrop along the east coast of the island of Iona within the Inner Hebrides of Scotland. The name was given to this sequence by Stewart in 1969, keeping it distinct from the Torridonian, which it resembles. It has now been assigned to the Wester Ross Supergroup. [1]

Three divisions are recognised; i) interbedded metasandstones and metasiltstones, ii) slaty semipelites and iii) conglomerates, the clasts of which are largely metamorphic in origin. The rock strata are steeply inclined to vertical. [2] [3]

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The Morar Group is a sequence of Tonian sedimentary rocks that have been subjected to a series of tectonic and metamorphic events since their deposition. Originally interpreted to be lowest (oldest) part of a "Moine Supergroup", this sequence now forms part of the Wester Ross Supergroup. They lie unconformably on Archean to Paleoproterozoic basement of the Lewisian complex. The contact with the overlying Glenfinnan Group of the Loch Ness Supergroup is everywhere a tectonic one, formed by the Sgurr Beag Thrust or related structures.

<span class="mw-page-title-main">Moinian</span> Geological rock formation in Scotland

The Moinian or just the Moine, formerly the Moine Supergroup, is a sequence of Neoproterozoic metasediments that outcrop in the Northwest Highlands between the Moine Thrust Belt to the northwest and the Great Glen Fault to the southeast and one part of the Grampian Highlands to the southeast of the fault. It takes its name from A' Mhòine, a peat bog in northern Sutherland.

References

  1. Krabbendam, M.; Strachan, R.; Prave, T. (2022). "A new stratigraphic framework for the early Neoproterozoic successions of Scotland". Journal of the Geological Society. 179. doi:10.1144/jgs2021-054.
  2. "Ross of Mull". Geological maps portal. British Geological Survey. Retrieved 1 March 2020.
  3. "Iona Group". The BGS Lexicon of Named Rock Units. British Geological Survey. Retrieved 7 July 2021.