Rift basin architecture and stratigraphical implications for basement-cover relationships in the Neoproterozoic Grampian Group of the Scottish Caledonides

A revised and expanded lithostratigraphy is presented for the lower part of the Dalradian Supergroup in the Central Highlands. Stratigraphical correlations combined with lateral facies Variations and geophysical studies are used to define a framework of NE-SW-trending marine basins that formed during a major phase of Neoproterozoic rifting. These basins extended rapidly and infilled with up to 5.5 km of turbiditic deposits, later thermal subsidence is indicated by the regional development of shallow marine shelf environments. The margins to these basins are characterized by lateral facies and thickness changes, stratigraphical omission and onlap relationships of both Grampian and Appin group strata onto a basement of predominantly gneissose strata. Whilst there is clear evidence for a stratigraphical and sedimentological break at the base of the Grampian Group there is presently insufficient structural or metamorphic evidence to prove an orogenic unconformity. Geochronological data confirm the presence of Precambrian events in the basement but have yet to do so in the cover.