A procedure for preparing an isopach map of Palaeozoic sediments situated beneath the Zechstein (Upper Permian) salt in an area within the Norwegian sector of the North Sea is described. The procedure
makes use of aeromagnetic and borehole data to prepare a map of the depth to the crystalline basement. In combination with published depths to the base of the Zechstein salt, based on seismic reflection data, the thickness of the sediments between the Base Zechstein and the top of the crystalline basement can be determined. The resulting isopach map of the pre-Zechstein-salt Palaeozoic sediments in our study area appears to be meaningful and defines local thicknesses in excess of 4 km. For a smaller part of the investigated area an isopach map of the pre-Zechstein-salt Palaeozoic sediments was produced from available seismic reflection data alone. The appropriate section of the larger isopach map compares well with this seismic isopach map, thus giving credibility to the method used.