Figure 4. Geological map of the North Sea Basin; Cenozoic isopach contours redrawn from Ziegler (1990). The Mesozoic graben faults, illustrated at the base of the Cenozoic series, demonstrate that maximum Cenozoic subsidence occurred above the central rifts. This relationship establishes the Cenozoic basin as a post-rift basin that formed above the Jurassic-Cretaceous dome.