Abstract

A gravity survey of some 300 stations has been made over the Turriff outlier of Old Red Sandstone, Aberdeenshire. Two reversed seismic refraction lines, each 4 km long, were shot in the northern part of the basin. Density and velocity contrasts were found with the underlying Dalradian rocks, enabling estimates to be made of the depth of the basin fill.

The southern half of the basin is structurally simple: N.-S. faulting, partly concealed, drops the basin floor to a depth of c. 1000–1500 m. Gravity anomalies in the northern part of the basin have been corrected for the effects of the Longmanhill and Strichen granites and offshore gabbros. The remaining anomalies, due to the O.R.S., have been coordinated with the seismic results. In the centre the floor is fairly flat with a depth of 1 km, but near the margins it rises by concealed faults to less than 500 m depth.

Tectonically, the long axis of the basin has been modified at the northern end by NE.-SW. trending faults along which movements were initiated by granite intrusions in the late Ordovician and continued until after the deposition of the O.R.S. The fault trends are considered in their regional context.

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