Sedimentology, stratigraphy, and U-Pb detrital-zircon geochronology of the Meall Dearg Formation, Stoer Group, Torridonian succession, north-western Scotland

Abstract

The Meall Dearg Formation is a c.1.2 billion year old sandstone, and represents the uppermost unit of the Stoer Group (Torridonian succession, north-western Scotland). Originally described as purely fluvial, the Meall Dearg Formation is here reappraised to represent coeval fluvial-channelised, floodbasin, and aeolian erg environments by facies analysis and petrographic methods. Evidence from palaeoclimate indicators points to humid conditions at time of deposition — inferred from clastic rather than evaporitic floodbasin strata. U-Pb detrital-zircon geochronology resolved provenance from the underlying Lewisian Gneiss Complex (comprising several juxtaposed terranes). Erosion from the Assynt, Gruinard, and Gairloch terranes provided most sediment supply. A statistical comparison of ages from the fluvial and aeolian deposits revealed that both underwent sediment transfer and/or were supplied from comparable terranes. The Meall Dearg Formation, a post-rift fill, is largely comparable to the coeval, pre-Rodinian Gardar-Rift sequence of Greenland.