The Boyndie syncline of the Dalradian of the Banffshire Coast

Abstract

The paper deals with the great fold affecting the Dalradian rocks exposed on the Banffshire coast, for which the name Boyndie syncline is now proposed. It is a large asymmetrical syncline whose axis runs north-north-east and emerges on the coast west of Banff. Its western limb is steeply inclined and, as Read showed, youngs eastward; over short stretches the rocks of this limb are intensely corrugated by subsidiary folds. The eastern limb is, as a whole, very gently inclined and is flexed to form the shallow Turriff syncline. Much of this limb is violently corrugated on a small scale. Variations in the attitude of the axial planes of small folds within the Boyndie syncline are described and discussed. It is suggested that the corrugation of the eastern limb is due to the squeezing out of incompetent beds from the core of the major fold. The central part of the steep western limb of the syncline has been intensely deformed and boudinage, mullioning and allied processes have led to the formation in this zone of a tectonic melange in which elonaated or lenticular masses of rock are enclosed in a less competent matrix. The axiil plunge of small-scale structures in this zone is very variable and is often steep. Preliminary petrofabric studies show that the preferred orientation of quartz is much stronger here than elsewhere in the fold. An oblique cleavage is imposed on rocks to the east and west of the intensely deformed sector. The possible significance of the structures seen on the Banffshire coast is discussed and their bearing on current views on the tectonics of North-East Scotland is debated.