Dr Maarten Krabbendam, British Geological Survey
The advent of modern dating techniques has, in recent decades, provided much better timing constraints on the deposition of Neoproterozoic sequences in Scotland, in Greenland and Svalbard. This has shown that the Neoproterozoic evolution of this north Atlantic province is dominated by three tectonic episodes: the Grenville-Sveconorwegian orogeny, the Renlandian orogeny and the rifting and formation of the Iapetus Ocean. In Greenland and Svalbard, Neoproterozoic sedimentary rocks can be divided into three ‘megasequences’, constrained by the three major tectonic episodes. In northern Scotland, however, the classic subdivision of Torridonian and Moine is at odds with these megasequences: a new stratigraphic framework is thus necessary. The oldest megasequence in Scotland is the newly named Wester Ross Supergroup, comprising the Iona, Sleat, Torridon and Morar groups of the Scottish mainland and Inner Hebrides, and the Westing, Sand Voe and Yell Sound groups in Shetland. These units were deposited c. 1000–950 Ma within a foreland basin to the Grenville Orogen. The second megasequence is the newly named Loch Ness Supergroup consisting of the Glenfinnan, Loch Eil and Badenoch groups of the Scottish mainland. These units were deposited after the Renlandian orogeny between c. 900–870 Ma and record Knoydartian orogenesis c. 820–740 Ma. The Dalradian Supergroup in the Grampian Highlands and Shetland belongs to megasequence 3; it was deposited c. ?800-480 Ma and records the opening of the Iapetus Ocean, ultimately leading to deposition of the passive margin Cambrian–Ordovician Ardvreck and Durness groups in the NW Highlands.