the southem part of the Norwegian sector of the North Sea

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 crys­ talline basement can be determined. The resulting isopach map of the pre-Zechstein-sa lt 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-sal t Palaeozoic sedi­ ments 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.