The Grampian Group: a major Late Proterozoic clastic sequence in the Central Highlands of Scotland

Abstract

A stratigraphic framework is proposed for the Late Proterozoic Grampian Group of the Scottish Highlands. The Grampian Group is divided into three subgroups, each defined by distinctive lithofacies associations reflecting different environments of deposition. The thin Ord Ban Subgroup, which is locally developed at the base of the Grampian Group on Speyside and Strath Dearn, consists of shallow marine shelf sediments in association with concordant amphibolite sheets. Elsewhere the Corrieyairack Subgroup, which is thickest around Loch Laggan, forms the lower portion of the Grampian Group and comprises a thick turbiditic clastic sequence laid down in deeper water during rapid basin subsidence. The Glen Spean Subgroup comprises the upper part of the Grampian Group and is thickest in the Atholl District. It is composed of shallow water tidal and deltaic deposits, marking a shallowing of the Grampian Group basin. Lateral facies changes and diachronous contacts are indicative of differential subsidence and the Grampian Group basin apparently developed and filled before the onset of regional subsidence which heralded deposition of the overlying Dalradian sediments. The possibility that the Grampian Group was unconformable on the structurally underly-ing Central Highland Division and Glenshirra Succession is currently unresolved.

The Dalradian rocks of the northern Grampian Highlands of Scotland

“…These are overlain in turn by the Glen Spean Subgroup, which represents a basin-shoaling succession from shallow marine to estuarine (Glover and Winchester, 1989;Glover et al, 1995;Glover and McKie, 1996). Such documentation of the stratigraphy and sedimentary history has transformed understanding of the Grampian Group depositional 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 record.…”

“…Variations in sediment supply and source area and the depositional processes are best documented for the Loch Laggan-Glen Roy area (Glover and Winchester, 1989;Key et al, 1997).…”

“…Details of primary sedimentological features are commonly preserved in the micaceous psammites and semipelites of this formation, despite simple upright F2 folding and the effects of metamorphic recrystallization under 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 amphibolite-facies conditions (c. 500-600°C, 5-8 kbar, Phillips et al, 1999 Glover (1989) and by Glover and Winchester (1989) incorporated palaeo-environmental interpretations.…”

Laurentian margin evolution and the Caledonian orogeny—A template for Scotland and East Greenland

“…The Greenland Caledonides -Evolution of the Northeast margin of Laurentia bounded by major crustal lineaments (Glover and Winchester, 1989;Banks, 2005). Despite regional deformation and metamorphism to amphibolitefacies conditions, the stratigraphical integrity and overall geometry of these basins has been preserved largely intact.…”

The Dalradian rocks of the central Grampian Highlands of Scotland

“…Further useful comments were made on the sedimentology by Glover and Winchester (1989) and Banks (2007), and on the structure by Lindsay et al (1989).…”