Correlation of depositional sequences in a structurally complex area: the Dalradian of Glenn Fearnach to Glen Shee, Scotland

Abstract

ABSTRACTThe stratigraphy of the Neoproterozoic Dalradian Supergroup has been formalised at group, subgroup and formation level, based largely on mapping in the SW Highlands of Scotland. Elsewhere, there has been a tendency for the lithostratigraphy to be fitted into this framework, implying that the lithostratigraphy represents basin-wide changes in depositional environment. The pitfalls of this ‘layer-cake’ approach are illustrated by interpreting the geology of the Gleann Fearnach to Glen Shee area of the Central Highlands, using the published maps of the adjacent regions. Attempts to correlate units into the Braemar area in the NE and into the Pitlochry area in the SW show considerable mismatch between the maps covering these areas, which has in the past led to invocation of geometrically unlikely arrangements of faults and slides to explain the lithostratigraphical distribution.The present study is the result of a different approach adopted during remapping of the Gleann Fearnach to Glen Shee area. Some basin-wide events, here suggested to be associated with key sequence stratigraphic surfaces, were identified. These principally relate to the deposition of Appin Quartzite, Boulder Bed and Ben Lawers Schist precursor sediments. Between these reference units the stratigraphy has been determined by detailed field mapping, and variation from the standard stratigraphy explained in terms of both the position within the depositional sequence and palaeogeography during deposition. This has led to an integrated solution which works on both sedimentological and structural grounds. There are local implications for the stratigraphy and structural geology elsewhere in the Scottish Dalradian, but, more importantly, it is an approach which must be more widely applied in order to make wider correlations beyond the British Dalradian to the rest of the Laurentian margin.