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.

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