The evolution and transport of the Tay Nappe

Synopsis A traverse through steeply inclined rocks north-west from Birnam is the equivalent of a vertical section at one point through the Tay Nappe. This traverse demonstrates increasing complexity and intensity of deformation at successively lower structural levels in the nappe. It suggests that the second episode of deformation (D2) at a low level was largely responsible for the emplacement of the nappe by simple shear, and that displacements of the order of 6 km during this episode can be demonstrated in the limited thickness of rocks exposed in the district. The earliest deformation (D1) induced two cleavages in the Southern Highland (Upper) Dalradian sandstones—one analogous to slaty cleavage and the other a tectonic striping produced by pressure solution. One set of folds, now downward-facing following D4 downbending, is associated with these cleavages. D2 deformation strongly modified the limbs and ‘facing’ characteristics of the D1 folds.